Europe's Quest for the Universe : ESO and the VLT, ESA and other projects

Europe's Quest for the Universe Lodewijk Woltjer

Europe’s Quest for the Universe ESO and the VLT, ESA and other projects

Lodewijk Woltjer

EDP Sciences 17, avenue du Hoggar Parc d’activités de Courtabœuf, BP 112 91144 Les Ulis Cedex A, France

Cover: THE VLT Array on the Paranal Mountain. © ESO. ISBN : 2-86883-813-8 Tous droits de traduction, d’adaptation et de reproduction par tous procédés, réservés pour tous pays. La loi du 11 mars 1957 n’autorisant, aux termes des alinéas 2 et 3 de l’article 41, d’une part, que les « copies ou reproductions strictement réservées à l’usage privé du copiste et non destinées à une utilisation collective », et d’autre part, que les analyses et les courtes citations dans un but d’exemple et d’illustration, « toute représentation intégrale, ou partielle, faite sans le consentement de l’auteur ou de ses ayants droit ou ayants cause est illicite » (alinéa 1er de l’article 40). Cette représentation ou reproduction, par quelque procédé que ce soit, constituerait donc une contrefaçon sanctionnée par les articles 425 et suivants du code pénal. © EDP Sciences 2006

CONTENTS

I. II. III. IV. V. VI. VII. VIII. IX. X. XI. XII. XIII. XIV. XV. XVI. XVII. XVIII. XIX.

Preface.................................................................................. Préface.................................................................................. Acknowledgements.............................................................. Introduction ........................................................................ The Development of European Astronomy during the 20th Century .................................................................. ESO, La Silla, the 3.6-m Telescope, Other Telescope Projects in Europe ............................................................................ Origin of the ESO VLT Project; The NTT ........................ Technological, Financial and Scientific Planning of the VLT............................................................................ Construction of the VLT .................................................... Sites for Telescopes ............................................................ The VLT Observatory: Adaptive Optics, Instruments, Interferometry and Survey Telescopes .............................. Ground and Space Based Optical Telescopes.................... Radio Astronomy; ALMA and SKA.................................... Europe in Space: ESA’s Horizons 2000 .......................... European Space Missions: IR, X- and Gamma Rays ...... European Space Missions: The Solar System .................. European Space Missions: The Sun and the Heliosphere .. Astroparticles and Gravitational Waves ............................ Looking for Planets and Life in the Universe .................. Publications ........................................................................ European Astronomy: Researchers and Funding ............ The Future .......................................................................... Epilogue .............................................................................. Notes .................................................................................... Acronyms ............................................................................ Index .................................................................................... Photo credits........................................................................

3 4 5 7 11 25 43 59 69 87 109 123 139 161 175 203 219 231 243 253 265 277 289 291 301 317 325

Preface

What a magnificent title, “Europe’s quest for the Universe”, for the opening of this new book by Professor Woltjer, which presents and expands on two grand themes. Since the days of Copernicus, Galileo, Tycho Brahe and Kepler, as a research community Europe has been at the cutting edge of science, in its incessant quest to understand the universe we live in. In this book we trace the history and development of more recent institutions such as the ESA and ESO. This is thanks to the great skill and experience of the author who, by writing this work, passes on the fruits of a unique and exceptional career. Great pride and optimism for European science comes across on reading these pages, all beautifully illustrated. Written to a high scientific level, this book provides the reader with a top quality reference on the subjects covered, and gives us ample reason to believe in a European research environment directed firmly to the future. The second theme is that knowledge and exploration of the universe are fundamental elements of the human psyche, a drive inherent in all of us to understand and discover our destiny. The Universe is a magnificent question which inspires scientific and technological development. At the same time it remains that star studded sky which acts as a source of wonderment and inspiration for our thoughts and dreams. Thank you Professor Woltjer for returning us, through this book, to the very roots of our humanity, and revealing to us such marvellous advances in understanding. Philippe BUSQUIN, July 2005 European member of parliament, Former European commissioner for Research

Préface

Quel magnifique titre pour l’ouvrage de Monsieur Woltjer “Europe’s Quest for the Universe” qui exprime deux idées fortes et l’évolution de celles-ci. L’Europe, comme espace commun de recherche, depuis Copernic, Galilée, Tycho Brahe, Kepler, a été à la pointe de la science et de cette quête incessante de compréhension de notre Univers. L’histoire et le développement des institutions plus récentes comme l’ESA et l’ESO sont retracés grâce à l’expérience et à la compétence de l’auteur qui, par le truchement de cet ouvrage, nous transmet les fruits d’une carrière unique et exceptionnelle. Quelle fierté et quel optimisme pour le savoir européen à la lecture de ces pages si bien illustrées et d’un haut niveau scientifique qui contribueront à nous donner une référence de très haute qualité sur les sujets abordés et nous fournissent toutes les raisons de croire en un espace européen de la recherche tourné vers l’avenir. La deuxième idée est que la connaissance et la conquête de l’Univers sont des éléments fondamentaux du besoin inhérent à l’homme de comprendre et de découvrir le sens de son destin. L’Univers demeure cette magnifique interrogation qui inspire le développement scientifique et technologique mais aussi le ciel étoilé propice aux rêves, aux réflexions et à l’émerveillement. Merci, Monsieur Woltjer, de nous replonger, grâce à votre ouvrage, aux racines de l’humanité et aux merveilleuses avancées de la connaissance. Philippe BUSQUIN, juillet 2005 Membre du Parlement Européen, Ancien Commissaire Européen à la Recherche

Acknowledgements

First of all I would like to thank Ulla Demierre Woltjer without whose active participation this book would not have come about. Jean Pierre Swings and James Lequeux read the whole book, Roger Bonnet, Daniel Hofstadt, Marc Sarazin and Giancarlo Setti some chapters and provided much information. Many persons supplied data or contributed in less formal discussions. I mention here Arne Ardeberg, Adriaan Blaauw, Roy Booth, Jacques Breysacher, Harvey Butcher, Giacomo Cavallo, Roger Cayrel, Thierry Courvoisier, Rodney Davies, Margo Dekker-Woltjer, Michel Dennefeld, Franca Drago, Hilmar Duerbeck, Daniel Enard, Peter Fischer, Robert Fosbury, Reinhard Genzel, Roberto Gilmozzi, Alvaro Gímenez, Michael Grewing, Einar Gudmundsson, Martin Harwit, Günther Hasinger, Martin Huber, Henning Jørgensen, Martin Kessler, Pierre Léna, Duccio Macchetto, Kalevi Mattila, Brian McBreen, Jorge Melnick, Evert Meurs, George Miley, Alan Moorwood, Antonella Natta, José Miguel Rodriguez Espinosa, Francisco Sánchez, Aage Sandquist, Richard Schilizzi, Hans-Emil Schuster, John Seiradakis, Peter Shaver, Boris Shustov, Jason Spyromilio, G. Srinivasan, Jean Surdej, Yasuo Tanaka, Virginia Trimble, Sergio Volonté, Malcolm Walmsley, Roland Walter, Robert Williams, Ray Wilson. Edmund Janssen, who drew the map in Figure VI, 3, Hans-Hermann Heyer and Claus Madsen searched the ESO archives for photographs. To all my thanks. I wish to thank Catherine Césarsky, Director General of ESO, and David Southwood, Director of the ESA Science Programme, for having contributed towards making the publication of this book possible, and EDP Sciences for taking the risk to publish it in color. Parts of this book were written while “chercheur associé” at the Observatoire de Haute Provence ; I thank the directors Philippe Véron, Antoine Labeyrie, Jean-Pierre Sivan and Michel Boër, as well as Mira Véron-Cetty, for their support. Other parts were written while “Rossi Fellow” at the Osservatorio Astrofisico di Arcetri, and I thank the directors Franco Pacini and Marco Salvati, as well as the chairman of the Astronomy Department Claudio Chiuderi for their support. Some sections were written during visits to the Raman Research Institute in Bangalore, and I thank the directors V. Radhakrishnan and N. Kumar for the friendly reception I received there.

Introduction

The progress of science depends on the technological development of its instrumentation. This is particularly true for the astronomical sciences where the study of remote objects requires sophisticated and costly detection techniques. In this book I shall analyze some of the large European astronomical projects, both on the ground and in space, their development during the last two decades, and their prospects in the future. While scientific progress is intimately related to technology development, both are contingent on professionals and funding, and I shall consider the situation with regard to both of these. This book is addressed to a varied audience: scientists who wish to see what is happening outside their own domain, students who look for fruitful areas of thesis research, functionaries who need some background for decision making, amateur astronomers interested in knowing what is going on in the profession, and also to an educated public that wants to get the flavor of what is behind the newspaper articles reporting scientific results and to know how European activities compare to what is being done elsewhere. The more detailed description of the development of the VLT, ESO’s Very Large Telescope, illustrates how a large technological project gets underway and after some pitfalls reaches completion. In the first half of the twentieth century observational astronomy was ipso facto astronomy done from the ground in the visible part of the spectrum. While in the USA ever larger telescopes were being built, in Europe developments were much more modest, partly owing to unsuitable meteorological conditions, but even more because private donors on the scale of an Andrew Carnegie did not exist here. In the early fifties some proposals were made to construct a large European telescope at a suitable location. Political and financial conditions for science were much improving, and in 1964 ESO, the European Southern Observatory, was founded by half a dozen countries as an intergovernmental organization; in the meantime most countries in Western Europe have become members. In writing this book, I have placed ESO at the beginning because of its increasing role in several areas of European astronomy. The early evolution of ESO has been well described by Adriaan Blaauw in his book “ESO’s Early History”1), so I shall give only a brief recapitulation and then sketch the origin of the VLT, which has brought Europe to the forefront of contemporary optical astronomy. Following a brief overview of the

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development of the astronomical sciences, subsequent chapters of the book deal with the origin, development, construction and siting of the VLT, its interrelation with the Hubble Space Telescope and with possible successors of these instruments. Also during the fifties radio astronomy became a major contributor to scientific progress. The European radio community has made many advances – in part by tying national facilities into a network, the EVN (European VLBI Network). The French-German-Spanish IRAM has been successful in radio astronomy at millimeter wavelengths. ESO entered this field with SEST, the Swedish-ESO Sub millimeter Telescope. ESO is the European partner in ALMA – the Atacama Large Millimeter Array, the major Europe-Japan-US venture in submm astronomy. With the advent of the space age other parts of the spectrum became observable. Thus, infrared, ultraviolet, X- and gamma-ray observations allowed entirely new objects to be discovered and studied. Moreover, possibilities opened up for in situ exploration of the solar system. At about the same time as ESO, the precursors of the European Space Agency ESA came into being. The ESA has constructed large facilities for space research. Again I shall be brief on early ESA history, since it is described by Roger Bonnet and Vittorio Manno in their excellent short book “International Cooperation in Space: the example of the European Space Agency”2), while early worldwide space science developments are comprehensively covered in “The Century of Space Science” edited by Johan A.M. Bleeker, Johannes Geiss and Martin C.E. Huber3). Subsequently, I deal with recent and future European scientific projects in space. Most of these have been developed in the ESA context, but also some national projects have had an important role. ESA and ESO are increasingly cooperating: The European Coordinating Facility for the Space Telescope is one example; joint studies in interferometry another. The latter may be essential in one of the most exciting astronomical subjects: the search for earth like planets and life. Also archiving the enormous data flows is a common interest of ESA and ESO. A more sociological discussion of European astronomy follows. How many astronomers are there in the different countries and how much is spent on astronomy? The end product of the astronomical activity consists of publications, and the productivity of the different communities is evaluated. The final chapter deals with the future and the difficult selection of expensive projects in a relatively less favorable economic and political environment, but ending on a positive note: the past achievements augur well for the future in which the countries now entering the EU should also play their part. The present book deals with European achievements and prospects which do not seem to have been described previously in a coherent way. Others have described their achievements elsewhere. Of course, comparisons are made with what other nations – in particular Japan, Russia and the US – are doing. Also cooperative projects with these countries play an

Introduction

9

important role. But is is important to realize that Europe has the full capacity to an autonomous role in science. Sometimes the necessary self-confidence seemed to be lacking among Europeans who measured their own success by how they are regarded across the Atlantic. The press services are not very helpful in this respect; even European results appear to become more respectable after a round trip across the ocean. Cooperation is a very good thing with mutual benefits. But such cooperation can only be profitable if it is based on equality, self-confidence and mutual respect. Europe has the capacity to autonomously plan its scientific future and does not have to try to fit into plans made elsewhere. It only has to strengthen its will to do so. Two caveats should still be made. In this book I discuss mainly the larger astronomical projects. Many smaller ones are also important, but including these would require a much more voluminous tome. Secondly, when I discuss collaboration, it refers to institutional collaboration. Individuals participate in an infinite number of collaborations with fellow scientists in their researches without regard to nationality or to political factors. This contributes much to the liveliness of the field and may also be beneficial in the creation of a more harmonious world.

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The Crab Nebula. First catalogued by Messier as M1, it was named by Lord Rosse who observed it in the middle of the 19th century with his six foot telescope in Ireland. It is the expanding remnant of the supernova which was extensively observed in 1054 in China and Japan. The Nebula remained mysterious until 1968 when a pulsar – a rotating neutron star – was discovered at its center. The strong magnetic fields of this star accelerate cosmic rays, including energetic electrons which produce synchrotron radiation in the nebular magnetic fields. That radiation is observed from the longest radio waves at 30-m through infrared, visible and ultraviolet light to the hardest X- and gamma-rays. In visible light it is seen as a smooth bluish continuum. The reddish filamentary structures on the image are due to emission lines from gas ionized by the ultraviolet radiation. Since almost all important cosmic processes may be studied in the Crab Nebula, it has been called the Rosetta stone of astrophysics. The image was taken with the FORS instrument (PI Immo Appenzeller) attached to ESO’s VLT, the Very Large Telescope.

I. The Development of European Astronomy during the 20th Century

Praised be your intellect, you interpreters of the heavens, you who understand the Universe, discoverers of a theory by which you have bound gods and men. Gaius Plinius Secundus1)

A visitor to one of the hundred odd observatories in the world early in the 20th century would have found some astronomers at work during the night at telescopes with diameter generally less than a meter. Some would peer through an eye piece and note down their findings, but photographic plates were coming into widespread use which gave a more quantitative and less subjective record of the observations. Mostly the astronomers would be measuring the positions of planets, asteroids and stars. By a comparison with previous observations they also determined their motions across the sky. The brightness (generally denoted magnitude) and the color of the stars were also ascertained, and some of the more venturesome professionals had begun to use spectrographs with which the stellar light could be split into different wavelength bands. This allowed the detection of absorption and emission lines in the spectra. By measuring their wavelengths precisely and comparing these with the wavelengths at which gases in the laboratory emitted or absorbed radiation, they could identify the main chemical elements present in the stellar atmospheres. Variable stars were also extensively studied, different types were recognized and their detailed characteristics identified. If he returned during the day, the visitor at the larger observatories would see numerous employees at work who would make the extensive calculations needed to establish catalogues of positions and motions of celestial bodies and to compare the results with theoretical models. Calculations were made with multiplication tables, tables of logarithms or very simple mechanical machines.

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The photographic plates used behind the telescopes were terribly inefficient; less than 1% of the incoming light (or as one would frequently say nowadays: of the incoming “photons”) was actually detected. Nevertheless, progress was made. By 1920 the magnitudes, colors, spectra and motions of many thousands of stars had been determined, and some ideas had been formed about their distances. So one could begin to construct more fact based models of how the stars are distributed in space. In fact, most stars were found to belong to a flattened system, with the Milky Way globally corresponding to its plane of symmetry. In this “universe” systematic streaming motions were suspected. Somewhat later it was concluded that the whole system is rotating. Whether there was anything outside this “universe” was unclear. Subsequently, evidence was found from photographic plates taken with the new 100-inch telescope on Mt. Wilson, California, that the faint luminous patch called the Andromeda Nebula was an independent stellar system, far away from our Milky Way Galaxy. Other “nebulae” were also resolved into stars and the “universe” was gradually growing in extent (Figure I, 1a).

Figure I, 1a. VLT image of the spiral galaxy NGC 1232; blue light comes from massive young stars which have formed recently in the spiral arms, while the yellow light around the center is contributed by older stars formed earlier in the history of the galaxy. To the left is a dwarf galaxy tied gravitationally to NGC 1232.

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Most of the early observatories had been constructed on small hills in the neighborhood of towns. As the towns grew and street lighting increased, they were sometimes moved a bit further out. In Europe most observatories were located in unfavorable climates, and in the north east of the US the situation was not much better. Turbulence in the atmosphere caused the stellar images to be smeared out over several arcseconds on the photographs. This made it hard to detect faint stars. It was G.E. Hale who decided that the solution was to go to the calmer skies in California. Raising enough private money, he founded the Mt. Wilson Observatory, which would be equipped with a 60-inch and later a 100-inch telescope. When the city lights of Los Angeles became too strong, a more distant site was developed at Mt. Palomar. As a result of these developments, the Californian astronomers were able to take the lead in investigating fainter stars and galaxies, and thereby to explore a much larger part of the Universe. This led to the discovery of the expansion of the Universe – the fact that more and more distant galaxies move away from us at larger and larger speeds. In our own Galaxy stellar populations with different chemical compositions were recognized. The important conclusion followed that most of the chemical elements were not created in the birth of the Universe, but have their origin in processes in the deep interior of stars. When stars die they may eject gas containing these elements out of which new stars may form (Figure I, 1b). Some of the European countries had founded observatories in their colonial empires, the UK in S. Africa, Australia, Canada and India, the French in Algeria, and the Dutch in Indonesia. Also Germany had considered the possibility. While these observatories collected useful data on a variety of objects, in particular on parts of our Galaxy invisible from Europe, they hardly contributed to a redirection of efforts in the mother countries. Of course, a few individual researchers could make visits to the Californian institutions, but most European observatories continued with the types of research they had been performing before. In addition, the second world war had a very damaging effect. So by 1949, when the 200-inch telescope at Mt. Palomar was inaugurated, the astronomical center of the world had largely moved to the US. In theoretical astrophysics much strength remained in Europe. This had led to a basic understanding of conditions in the stellar atmosphere and interior and of the nuclear reactions which produce the luminous energy radiated from the surface. A beginning had been made with studies of stellar evolution, while also the dynamics of our Galaxy and the orbits of stars therein were being explored. However, the rise of theoretical physics in the US (in part due to European refugees) and the early availability there of powerful computers also threatened the European pre-eminence in the theoretical domain. Four very different developments led to a rebirth of European observational astronomy: the discovery of radio waves from cosmic sources,

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Figure I, 1b. VLT image of the “planetary nebula” M27, a gaseous shell ejected by the star at the center. The interstellar gas may become enriched in elements synthesized in the star, which now ionizes and excites the shell. Different densities and temperatures in the gas lead to different emission lines and thereby to different colors in this image.

the availability of government money for research, the development of air travel and European cooperation. Soon space research would add further possibilities for observations of celestial X- and gamma-radiation and in the infrared part of the spectrum. In the appendix to this chapter the definition and units of measurement of the electromagnetic spectrum are indicated for future reference. Cosmic radio waves had been serendipitously discovered in 1933 by K. Jansky, an engineer at AT&T, but until the end of the war only some very limited follow up had been done. So the field was wide open. The poor climate in Europe did not matter, since radio waves pass through clouds and atmospheric turbulence unhindered, except at short mm wavelengths. Some of the leftover military radar equipment could be quickly converted to astronomical use, and so the cost of the first radio telescopes was modest. It soon turned out that the scientific returns were very large. Radio emission due to cosmic ray electrons throughout the Galaxy could be extensively studied.

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The 21-cm emission line emitted by diffuse interstellar hydrogen gas provided a means for studying the whole galaxy without the problems associated with absorption by interstellar dust which had stymied the attempts to derive its structure by observing stars. Discrete sources of radio emission were discovered which turned out to be frequently associated with remote galaxies. So here was a whole new universe, and scientists in Europe, Australia and the US started its study at about the same time in conditions of equality (Figure I, 2). However, the radio sources that were discovered had to be identified with visible objects to determine their nature and distances. Since even strong radio sources are frequently very faint optically, this still required the large telescopes in the western US. An important contribution to the American prominence in astronomy had been made by the availability of ample private money. During the period of the wildest capitalism huge fortunes had been built, and some of the owners of these or their heirs were fascinated by the astronomical universe or liked having telescopes carry their names. Thus, Carnegie had financed Mt. Wilson and Hooker had contributed much to the cost of the 100-inch telescope. Even very recently the Keck Foundation provided an important part

Figure I, 2. The 76-m radio telescope near Manchester. Completed in 1957, it illustrates the rapid growth of radio astronomy in Europe after the war. For 15 years it was the largest radio telescope in the world.

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of the funding for the two 10-m telescopes at Mauna Kea, Hawaii. No similar tradition existed (or exists today2)) in Europe, and so most observatories lived a more precarious existence. After the war, and because of the important role science and technology had played for the winning side, this changed and governments began to consider it their function to sponsor research. With radio astronomy having some connections to radar and telecommunications, both funding and competent engineers were available. Typical optical observatories had resident staff. Especially in poor climates it was necessary to use every clear hour, and this could be done only when the astronomer lived on the site. However, with air travel becoming cheaper and faster, a different modus operandi became possible in which observatories could be located in optimal places anywhere in the world and astronomers would travel there just for an observing period – initially months or weeks, nowadays frequently no more than a few days. Constructing large observatories in remote places was expensive. To provide adequate funding remained difficult for individual governments. With Europe gradually becoming more unified, it seemed appropriate to consider the possibility of financing expensive scientific installations on a wider basis. Thus, CERN – the European center for nuclear and particle physics – was founded at an early date. Later ESO, the European Southern Observatory, and ESA, the European Space Agency, followed. These collaborations created the intellectual and financial basis for Europe to have the ambition to compete on the world level. By now, more than a third of all astronomy spending in Europe is done on a European rather than on a national basis. Few things happen very fast in Europe and it took a rather long time before ESO was organized. Its first “large” (3.6-m) telescope was completed only in 1976, some 23 years after it had been first proposed. In the meantime, other telescopes of similar size were being developed by several countries. Not surprisingly, many European astronomers wanted to continue to do the things they had done before: to study the distribution and motion of the stars in our Galaxy, variable stars of every kind, the motions of double stars, stellar atmospheric structure, comets and asteroids. Even though valuable research was done in these areas, European optical astronomy lacked some of the excitement that prevailed on the other side of the Atlantic, where the unknown deeper reaches of the Universe were being explored. The difference in astronomical orientation is conspicuous if one compares the ambitions for the Palomar 200-inch telescope and that for ESO. In his 1928 proposal for the construction of a 200–300-inch telescope, Hale3) indicates the principal areas of research which three quarters of a century later have lost none of their interest, though today we might phrase them somewhat differently. The topics were: The structure of the Universe. The structure of our Milky Way Galaxy.

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The evolution of stars. The successive stages in the development of spiral galaxies (“the greatest of these problems”). The Universe as a cosmic laboratory to investigate the nature of matter. In a much narrower way the preamble to the ESO Convention places the emphasis strongly on the second item of this list, with the following statement: “Considering that the study of the Southern celestial hemisphere is much less advanced than that of the Northern hemisphere, that the data on which the knowledge of the Galaxy is based are accordingly by no means of the same standing in the different parts of the sky and that it is essential to improve and supplement them in all instances where they are inadequate,…” This is effectively a statement that the principal reason for founding ESO was to fill in the missing southern parts of the structure of our Galaxy, including its satellites the Magellanic Clouds. The first instrument built for the 3.6-m was a stellar photometer mainly suited for Galactic research. Certainly such research was important, and it had provided the justification for placing ESO’s facilities in the southern hemisphere. But for European astronomy to partake in the newer developments, a change of attitude and more suitable instrumentation would be needed. Several astronomers were well aware of this, and in some places researches were initiated on extragalactic topics, on interstellar matter and on high energy astrophysics. When ESO finally could organize a scientific division, the emphasis was mainly on the new domains. Young postdocs staying for a few years before returning to national institutes would develop cooperations in these subjects and later contribute to the creation of a strong coherent European astronomical research community. The increased coherence of that community would allow ESO thereafter to become much more ambitious and to build the world’s top telescope, the 16-m equivalent VLT. As in radio astronomy, the development of high energy astrophysics in Europe was very rapid once the essential tools became available. Less than five years after Sputnik, the UK observed cosmic-rays and solar X-rays with the Ariel 1 satellite. Particularly successful were Ariel 5 (1974) which made an X-ray sky survey and Ariel 6 (1979) which determined cosmic-ray composition. In 1974 the Dutch launched the ANS satellite with X-ray instrumentation and the Germans the first of the Helios spacecraft to study the solar wind. In the meantime, ESRO, later transformed into ESA, the European Space Agency, had launched its first satellite ESRO-II (1968) which observed solar X-rays. Among the European astronomical satellites TD-I (1972) for uv operations and COS-B (1975) for γ-rays were quite successful. IUE (1978), the International Ultraviolet Explorer, a NASA-UK-ESA collaboration, was also important in integrating the astronomy and space communities in Europe. Thereafter ESA missions became larger, more competitive and well centered

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on the newer astronomical research areas: EXOSAT (1983) and XMM-Newton (1999) in X-rays, INTEGRAL (2002) in γ-rays, ISO (1995) in the infrared, supplemented by a participation in the Hubble Space Telescope from 1991 onward, gave European astronomers access to much of the wavelength range of space astronomy. In addition, the national X-ray satellites ROSAT (D, 1990) and BeppoSAX (I, 1998) made major contributions. Hipparcos (1989) gave Europe the lead in astrometry, determining positions and motions of 100,000 stars. In the exploration of the solid bodies of the solar system Europe was a latecomer. Of course, planets, asteroids and comets had been observed with telescopes on earth, but only limited results could be obtained from large distances. The first space mission to observe such an object from close by would be Giotto in 1985, which obtained the most detailed information ever on a cometary nucleus. It took 18 years before the next such European mission arrived at Mars. Both Russia and the US had left Western Europe far behind in planetary exploration. Ulysses (1990) and SOHO (1995), both joint missions with NASA, and Cluster (2000), continue to study the Sun and the heliosphere with advanced instrumentation. All of the IR, X- and γ-ray missions require much follow up with optical telescopes, and it is fortunate that ESO is now able to provide unique possibilities for this with the VLT. When today one looks at European astronomy, one sees a vibrant community active and competitive in all the exciting areas of research on the Universe, its contents and evolution. Not surprisingly, in parallel with the increased instrumentation also the number of professional astronomers has much increased (Figure I, 3). Less than a century ago they were rare and frequently considered as oddballs with rather doubtful economic prospects. Few parents would approve their daughter marrying an astronomer! Their nightly work also set them apart from the typical social schedule. Today being an astronomer no longer makes one very different from people in other scientific professions. In the developed world there are typically ten to twenty astronomers per million inhabitants. And while most are not particularly rich, their material prospects are no different from those in other academic professions. They used to work as individuals or in groups of two or three. Nowadays it is not unusual to see research projects of fifty scientists, postdocs and graduate students. This has had several consequences. Such groups tend to have a hierarchical structure, with the leaders not only controlling the research of the more junior staff but also their economic well being. This would seem to be unavoidable, but it makes the jobs of the junior staff less attractive. All of this is accompanied by a certain “industrialization” of the research, with projects defined and executed on financial and time schedules. Since many staff members are needed in such projects and insufficient long term academic positions are available, a system of temporary postdocs has arisen with appointments on time scales of typically two or three years. This was not too serious when

Total reflecting surface area in m2 of fully steerable telescopes/number of members of the International Astronomical Union (divided by 10)

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1000

100

10

1 1900

1950

2000

Year Figure I, 3. Astronomers and telescopes. The total reflecting surface area in m2 of fully steerable telescopes for the world (green) and for Europe (blue) compared to the number of members of the International Astronomical Union (divided by 10, in red) for different years. Exponential growth is noticeable in all, though now the numbers of IAU members are beginning to flatten off. It is seen that after the war Europe had fallen far behind in telescope construction, but that by now it has caught up again. The cross indicates what would be the result of the construction of OWL (Chapter VIII).

overall employment increased and more continuing appointments were available but now long term positions are not easy to find, and a large number of postdocs are floating around from one temporary position to the next. Some ultimately quit and take jobs in industry or government. Young astronomers tend to be well qualified in subjects like programming, image processing and the handling of large data sets. In addition, they are used to

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arrive at conclusions concerning systems about which insufficient information is available. So, at least in some European countries, they fit relatively easily into jobs in insurance, banking and government planning offices. For example, in Holland two out of three people with a degree in astronomy wind up in nonastronomical positions. There is nothing wrong with this, but it implies that astronomy education should not be too narrow. Of course, some astronomers also become science teachers in high school. Nevertheless, one may wonder if the postdoc system has not been overstretched. Especially at a time when alternative jobs become also more difficult to obtain, the prospects become so uncertain that many of the more perspicacious students may choose other directions. To summarize, there thus were three phases. Till the early years of the 20th century astronomy was largely a European affair. During the subsequent decades, the American dominance was established partly by a better funding situation and also by the unfortunate developments in Europe which paralyzed research and caused many prominent researchers to leave, never to return. After the war ended European astronomy began a slow recovery process which accelerated in the seventies and eighties. By now Europe has reached again a position of equality in most astronomical fields and leadership in some. Two fundamental factors have contributed to this: a well educated pool of young talent and nearly adequate funding. If these would begin to be lacking, a decline would be rapid. In this respect, some fears for the future are justified. At the political level in Europe there is much talk about the “knowledge based economy”, while at the same time the financial underpinnings of such an economy are being weakened. Besides, the evolution of high schools and universities is not always encouraging. So what around 1975 were the main problems that the world astronomical community perceived as essential to tackle, and which have shaped astronomical technology in the subsequent decades? Perhaps clearest was that only a very small part of the Universe had been surveyed. A few quasars at larger redshifts were already known, but since they were not understood, they did not yet help much in cosmological studies. The key to further progress was the ability to observe fainter galaxies at greater distances and also fainter stars in our own Galaxy. Second, it was also evident that we had only a very washed out view of astronomical objects ranging from remote galaxies to the planets. Much of the essential physics would only be seen when angular resolution would be improved by better observational techniques or in the case of our solar system by in situ studies. Third, we had seen enough to realize that the view at visible wavelengths was very incomplete. More satisfactory radio observations were in sight, but in the IR, X- and γ-rays and in the study of particles like neutrinos or of gravitational waves we had just scratched the surface sufficiently to know that our ignorance was complete. Thus, the trio that since then has dominated progress was increased sensitivity, increased angular resolution and increased wavelength coverage.

Development of European Astronomy

21

Increased sensitivity could be achieved by larger telescopes and by more efficient detectors. Some of the first CCD detectors were developed for space imaging; infrared detectors were developed by the military for night vision devices and other purposes. X- and γ-ray and particle detectors were developed by physicists for a variety of aims. By now CCDs of large formats and low noise are abundantly available; even a 100 € camera has a CCD. To obtain better sensitivity and angular resolution, larger telescopes now are needed. We have a general idea how to build these, but more and more the cost is a limiting factor. So to the above mentioned trio we have to add a fourth: cost reduction. The story of ESO, ESA and European astronomy in general over the last 30 years has been one of finding better and cheaper solutions to instrumental problems so as to be able to afford what we can conceive. Of course, the scientific utilization of our instruments is the ultimate aim. But it may well be that the good scientific use of these instruments is easier to achieve than their development at acceptable cost. Observational results will remain isolated facts if there is not a theoretical framework in which they find their place and for which at the same time they provide the foundation. Such a framework is also needed to see which future observations are most likely to increase our understanding. Thus, theoretical research is an essential part of astronomy, though its detailed aspects are outside the scope of this book.

Annex: Electromagnetic Radiation Different aspects of electromagnetic radiation are described in terms of waves or particles. When we discuss diffraction of light through a small opening or interference of light beams, the wave description is more convenient; when we study the effect of light on a solid state detector like a CCD, it is simpler to think in terms of photons ejecting electrons from the material. However, both descriptions refer to the same underlying physical phenomenon. In image forming systems (lenses, mirrors) the image is formed by the interference of refracted or reflected light beams. An important result concerns the angular resolution – the minimum separation in angular measure (degrees, arcminutes, arcseconds) which allows us to see two stars as separate objects. At a wavelength λ the angular resolution θ of a telescope with a diameter d is given approximately by θ = 200 000 λ/d arcsec, where λ and d are in the same units. Thus, at visible light with λ § 0.5 μm a telescope with a circular aperture of 1 meter diameter has an angular resolution of 0.1 arcsec. If we inspect two stars or other objects at a distance D, the linear separation l corresponding to the angle θ is about θD/200 000 and, therefore, the linear resolution l = λD/d. Thus, with our 1-m telescope we

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22

would be able to see details on the moon (D = 400 000 km) 200 m in size. This would, in fact, be the case in space. However, from the ground the angular resolution is degraded due to atmospheric turbulence to values typically ten times larger, unless adaptive optics (Ch. VII) is implemented. Astronomical measurements extend over a range of a factor of about 1021 in wavelength. Three types of units are commonly employed in different parts of the spectrum: wavelength, frequency and photon energy (Figure I, 4). In the radio part of the spectrum frequency ν is most commonly used, or alternatively wavelength λ. The relation between the two is νλ = c, with c the velocity of light 3 × 108 m/sec. Frequency is measured in Hz (cycles/sec). In the IR, visible and uv it is more common to use wavelength. In the X-ray region of the spectrum the eV (electronvolt) is the unit of choice, with a photon energy of E expressed in eV corresponding to a wavelength λ expressed in μm by the relation E (eV) = 1.24/λ (μm).

Wavelength atmospheric transparency frequency/energy name

km

MHz

m

GHz Radio

μm

mm

nm

eV

THz IR

keV V

UV

X-rays

MeV

GeV

TeV

γ-rays

Figure I, 4. The electromagnetic spectrum. The tickmarks correspond to factors of ten, but those of the Hz and eV scales are not continuous. The prefixes n, μ, m, k, M, G and T correspond to 10-9, 10-6, 10-3, 103, 106, 109, 1012. The blue parts of the spectrum in the figure cannot be directly observed from below the earth’s atmosphere. Above 10 GeV indirect measurements are possible by observing the interaction of the very energetic photons with the atmosphere. The atmospheric transmission in the IR is more complicated than indicated here with some narrow “windows” in the 2–30 μm and the 200–1000 μm spectral domains. Common terminology for the latter is “submm” or “far IR”, while “near IR” refers to 1–2.5 μm. Terminology at shorter wavelength is less well defined, with “near uv”, followed by “far uv” and “EUV”, the extreme ultraviolet. The EUV gradually becomes “soft X-rays” (” 1–2 keV), “hard Xrays” (• 5–10 keV), and “soft γ-rays” with a considerable overlap.

Development of European Astronomy

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The southern Milky Way and the Magellanic Clouds (photo: C. Madsen). Just under the Small Magellanic Cloud is the second brightest globular cluster 47 Tucanae, just above the bar of the Large Cloud the Tarantula Nebula, a region of dense gas and intense star formation. The dark area in the Milky Way is the “Coal Sack” due to a nearby cloud of dust which blots out the stars behind it; at its top is the star α Crucis, which with the three bright stars to the left constitutes the “Southern Cross”. The two bright stars below the Coal Sack are α and β Centauri. Just outside this image to the left are ω Centauri, the brightest globular cluster in the sky, and Centaurus A, the nearest radio galaxy (Fig. IX, 1).

II. ESO, La Silla, the 3.6-m Telescope, Other Telescope Projects in Europe

Among the other most remarkable spectacles which we have beheld, may be ranked the Southern Cross, the cloud of Magellan and the other constellations of the Southern hemisphere. Charles Darwin1)

During a visit to Jan Oort in Leiden, Walter Baade, a German astronomer working in Pasadena, gave the impetus to the idea of a joint European observatory. At Lick Observatory in California a 3-m telescope was under construction, and the proposal was to quickly build a copy and place it in the southern hemisphere which was the optimal location for the study of our Milky Way Galaxy and the Magellanic Clouds. Since some connections already existed to South Africa, the first thought was to go there. The emphasis on Galactic research was not unnatural since because of their relatively small telescopes European astronomers had not participated much in the study of remote galaxies which had remained the prerogative of the large Californian telescopes. As a consequence, many of them saw such an observatory as a means of extending their researches in stellar and galactic astronomy. By a fortunate coincidence, preparations for CERN, the Center for European Research in Nuclear Physics, were just coming to a satisfactory conclusion and so a ready made model for a European scientific research organization was in place. Nevertheless, it took another decade before the convention establishing the European Southern Observatory was agreed on (1962) and ratified by five European parliaments (1964): Belgium, France, Germany, the Netherlands and Sweden, followed in 1967 by Denmark. The United Kingdom had participated in some of the discussions. However, the Commonwealth Astronomer, later Astronomer Royal in England, R.v.d.R. Woolley strongly opposed a project with the Europeans, while the eminent scientist F. Hoyle,

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seeing the governmental lawyers at work armed with French-German dictionaries, concluded “I thought that an observatory organized this way is not going to work”2). So in 1961 the UK decided on a joint project with Australia instead. History repeated itself in 1987 when I had discussions with the UK representatives on participation in the VLT, which were followed by the UK joining the Gemini project of the US. Finally, when the superiority of the completed VLT had become clear and even larger telescopes were beginning to be discussed, the UK joined ESO in 2002. It had to pay a substantial entrance fee without its industry having had a chance to profit from the project. In the meantime Italy and Switzerland (1982) and Portugal (2001) had also become full members. Finland followed in 2004. Well before the convention was signed, a beginning had been made with studies of possible sites in South Africa, where several European astronomers had scientific contacts and where a functioning observatory already existed. In retrospect, the long delay in getting ESO started may well have been advantageous; by 1964 the superiority of sites in the Andes had become clear3) and it was still possible to opt for a place in Chile. The ESO convention specified that the principal instrument would be a telescope of “about 3 meters aperture”. At the time it was considered necessary that such a telescope have three focus positions (Figure II, 1): a prime focus for very deep photography and low resolution spectroscopy, a Cassegrain focus for photoelectric photometry and medium resolution spectroscopy and a fixed coudé focus for very high resolution stellar spectroscopy. Since remote control was still beyond the horizon, it was necessary to have the observer in a “prime focus cage” to guide the telescope and to change the photographic plates. Because such a cage had to accommodate a human being it could not be so very small, and with a 3-m telescope an unacceptable amount of light would be intercepted by the cage. So finally the wording of the convention was stretched and the aperture enlarged to 3.57 m. The long delay before the ESO convention was concluded had also some negative consequences. While in the sixties a 3.6-m telescope in the southern hemisphere would have been unique, by 1976 the 4-m US telescope at Cerro Tololo and the Anglo-Australian 3.9-m had already been operating for more than a year. Even more serious for ESO, some of its member countries were building their own 3.5-m class telescopes. France was involved with Canada in the 3.6-m CFHT (Canada-France-Hawaii-Telescope) on the excellent site on Mauna Kea at 4200 m altitude. In Germany Zeiss was building a 3.5-m telescope for the Max-Planck-Institut für Astronomie; though ultimately placed on Calar Alto in Spain, it had been foreseen for the Gamsberg in Namibia. A 3.5-m telescope was planned by the Italians for Castel Grande in southern Italy, though it was completed only some twenty years later at La Palma in the Canary Islands. Thus, ESO had lost its preeminence in the southern hemisphere, while in a European context it was in

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27

a

b

c

d

Figure II, 1. Different types of telescopes. a – prime focus with only one reflection on a concave mirror; b – Cassegrain with two reflections on a concave primary and a convex secondary; c – Nasmyth, with a flat tertiary mirror sending the light through one of the axes; d – coudé with a number of flat mirrors which allow the focus to be at a fixed location while the telescope moves. A representative light-ray is indicated in red, while the mirrors are shown in white and the focal position as a green dot. The Nasmyth focus is particularly suited for an alt-azimuth telescope. The number of flat mirrors in the coudé depends upon the layout. At each reflection on aluminum coated mirrors about 15% of the light is lost at visible wavelengths.

competition with several equivalent national projects. Why have a costly European venture at a level attainable by the major countries in Europe by themselves? Initially the 3.6-m telescope project had been placed in the hands of a well qualified engineer, W. Strewinski. However, neither he nor ESO’s management had appreciated the magnitude of the task. By 1970 alternative solutions were looked for, and this led to the creation of the ESO Telescope Project Division on the CERN campus with a generous contingent of CERN personnel temporarily added to the ESO staff. This finally resulted in 1976 in the successful installation of the 3.6-m telescope (Figure II, 2) at La Silla some 500 km north of Santiago de Chile. As a consequence of its history,

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Figure II, 2. The 3.6-m telescope at La Silla. From bottom upwards the Cassegrain cage inside which spectrographs or other instruments are located, the primary mirror (invisible), the declination (celestial latitude) axis attached to the horseshoe like structure at the end of the polar axis on the right, and near the top the Cassegrain secondary with some baffles or the prime focus cage. Initially, an observer was present in one of the two cages, but subsequently remote controls were installed.

it was of conservative design and had cost a great deal of money (68 MDM4) or 78 M€ in 2004 value, including its housing and personnel costs). Hardly any instrumentation for the effective use of the telescope had been developed. All the 3.5–4-m telescopes constructed during the seventies share this conservatism. Some relatively small differences in the mechanical design occur, but globally all follow the overall pattern set by the 200-inch telescope

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29

on Mt. Palomar. A prime focus cage accommodating an observer, a Cassegrain cage behind the primary mirror and a fixed coudé focus for heavy auxiliary equipment reached after extra reflections, the telescope rotating around an axis pointing towards the celestial north or south pole so as to track the daily motion of the stars with a rotation around this axis. Only the astronomers in the USSR had had the courage already in 1960 to adopt an altazimuth (one horizontal and one vertical axis) design for the 6-m telescope. To some extent they were forced in this direction by the large weight of the 6-m mirror. From a mechanical point of view there is much advantage to have the telescope tube move only in a meridional plane on a rotating platform, thus avoiding the complex mechanical stresses of the polar mount. This leads to important cost savings (see chapter III). Also heavy equipment may be mounted easily and accessibly at the two Nasmyth foci. The inconvenience is the fact that the telescope has to be driven in two coordinates at varying rates, which at the time of more primitive computers was not a trivial matter. However, when refraction and telescope flexures are taken into account, even a polar mounting requires more than just an axial rotation. More serious is the image rotation in an alt-azimuth mount which has to be compensated. At ESO not much discussion seems to have taken place on a possible alt-azimuth mounting5). There was a general feeling that the American engineers knew what they were doing and that one should not deviate too much from their designs which had been proven to function well. Of course, this implied that the technology was not necessarily the newest. A certain conservatism was perhaps justified by the fact that the observatory, as specified in the convention, looked very much like a one shot affair to provide a European observing capability. If one would have considered the convention program as a first step in a long range enterprise, the need for an independent European capability in telescope technology would have been clear. Of course, in all of this one has to take into account that ESO came into being at a time of very rapid developments in computers and detectors and that many aspects were still not clear at the time decisions were made. Nevertheless, it remains surprising that cost-to-benefit considerations were so largely absent. Perhaps the ample availability of money in those days provides an explanation. Progress on ESO’s 3.6 m telescope had been slow, but instrumentation developments were in a catastrophic state. The only instrument being designed was a 4-color photometer/polarimeter. Though the instrument, developed by Alfred Behr, was excellent, it was hardly the most urgent one for a large telescope. Following numerous test nights, it was in operation for only 24 nights before being decommissioned. Much discussion had taken place about the construction of a large coudé spectrograph. To maximize the optical path the building plans at some stage had become quite fantastic: below the round dome the coudé floor would be square. Along the diagonal this would increase the available length by ¥2. Finally, fear for the image

30

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quality as a result of this awkward aerodynamical shape led to its abandonment6); undoubtedly this also reduced costs. Because of the high cost of the coudé spectrograph, it had been decided to construct next to the 3.6-m telescope a 1.4-m Coudé Auxiliary Telescope (CAT). During the time that the large telescope would be used for other purposes, the CAT would allow the spectrograph to be used for the observation of brighter stars. The coudé focus also had a major impact on the telescope design with three large flat mirrors, needed to bring the light from the moving telescope to the stationary focus. By the time the 3.6-m telescope was completed, classical coudé spectrographs were being abandoned in many observatories since more compact and efficient Cassegrain instruments had been developed. In fact, only two of the three flats have been installed in the telescope and the classical coudé focus has never been implemented. When I came to ESO in 1975, it was evident that there was no real plan to effectively use the 3.6-m telescope for contemporary science. There also would be no suitable instrumentation to attach to the telescope. All of this reflected the absence of any scientific identity of ESO. In particular the French had been insisting that ESO be an “Observatoire de mission” with only the staff needed to run the telescopes. Instrumentation would be decided by an Instrumentation Committee and built largely in the national institutes, while scientists residing in their home institutes would decide what programs to execute. This approach was inadequate in giving the instrumentation the necessary coherence and realism. In December 1972 my predecessor, Adriaan Blaauw, had tried to get the ESO Council to agree to the creation of a small “scientific group” in Geneva, which I would be heading. Instead, Council offered a visiting appointment to discuss with the member countries the instrumentation issues. This did not seem a particularly attractive job. The issue came again to the fore in 1974 when a new Director General had to be found. Council had begun to realize that things were not going well and so became more receptive to a change of policy. Still a long period of wrangling followed which lasted more than a year. This began when I was to be appointed. I had made the creation of an in-house scientific group a condition for taking the position. Council met in closed session to discuss the appointment and was expected to come to a rapid conclusion, but for several hours nothing happened. Inside the meeting room, however, the situation was dramatic. The French President had received the agreed view of Council as to what he would tell me. At some moment during this process, he felt that his honor had been questioned by the German Vice-President. In true gallic tradition he resigned as President. The Vice-President automatically became President, but immediately also resigned. Since some decision had to be taken, J.H. Bannier as the most senior member of Council assumed the presidency, and finally the appointment was made in a provisional way. Several weeks later three Dutchmen: the Director General A. Blaauw, the interim President J.H. Bannier and I met to see how to

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proceed further. At the December Council meeting I was to present a complete plan for the future of ESO with proposals for both Chile and Europe. If these were acceptable to Council, then my appointment would be confirmed. No one seems to have wondered what to do four weeks later if no agreement were reached. However, everything went smoothly, because several issues were left hanging. Half a year later the disagreement with the French came again to the fore, with an implied threat that they might leave the organization if outvoted. As a delegate of one of the small countries said, they would support me entirely except if this threat were to become fully serious. Some discussions between a few delegations took place outside, and the final result was an agreed resolution scribbled on a sheet of paper. Before this came to a vote, someone wondered if one should not ask the Director General’s opinion. If only because of the way in which that resolution had come about, it was obviously unacceptable. Following this, Bengt Strömgren, the President of Council, took the piece of paper with the resolution in his fist and crumpled it. An absolute silence followed with everyone waiting to see what would happen. Strömgren’s prestige was such that no one dared to say anything, and he simply resumed the discussions. The final result was that a beginning of a scientific group was agreed, while Jean-François Denisse would travel to Chile with me to evaluate the situation there. That visit was decisive. He saw there that the drastic remedies I was proposing were fully justified. Moreover, he discovered that the French complaint of a lack of French staff was unfounded: people like Jacques Breysacher and Daniel Hofstadt turned out to be French rather than German! Soon after this visit a final compromise was reached. In the subsequent twelve years I enjoyed excellent relations with all delegations in Council, which finally led to the unanimous approval of the VLT project. It shows the importance of forcing the issues early, rather than having them fester on unsettled for a long time. When I arrived at ESO, it was clear that to effectively use the 3.6-m telescope for contemporary science the absolute necessity was to have a simple spectrograph for the observation of faint galaxies, nebulae and stars. Since no time was available for an optimized design, a ready made Boller & Chivens spectrograph was purchased. The Instrumentation Committee had little love for this spectrograph, claiming that the optics were not optimal. However, it was the only instrument that could be acquired rapidly. Because of the lucky absence of some members at the decisive meeting, the IC finally agreed. For some 6 years this remained the only spectrograph at the 3.6-m suitable for observing faint objects. Especially with the newer detectors it was quite successful. During 1976 a new instrumentation plan was developed (largely based on a proposal of Johannes Andersen at Copenhagen and Daniel Enard at ESO) which in addition to the low resolution spectrograph contained a crossdispersed échelle Cassegrain spectrograph for resolutions of the order of

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30,000. Furthermore, a high resolution (λ / Δλ ≈ 100,000) coudé échelle scanner (CES) would be constructed for use with the 1.4-m CAT exclusively. This allowed the 3.6-m and CAT telescopes both to be used 100% of the time and to “postpone” the extensive work needed to implement the coudé focus of the 3.6-m, which still had many adherents. This liberated the personnel needed for more urgent instrumentation. The instrumentation plan also foresaw the introduction of new electronic detectors as an essential part of all instruments, replacing photographic plates. The Boller & Chivens spectrograph served the ESO community well for nearly a decade. However, its reflecting optics caused significant light losses, though it was necessary for covering a large wavelength range. In the meantime new glasses had been developed by Schott in Mainz which made it possible for Enard to design an all-transmission spectrograph containing only lenses and prisms. With the ESO Faint Object Spectrograph and Camera, EFOSC, the sum of all the light losses amounted to less than 25%. In addition, the lenses were so arranged that the optical beam was parallel over a certain distance and here filters and dispersive elements could be placed. These were mounted on remotely controlled wheels. By rotating these one could obtain images or spectra with different characteristics. This very much enhanced the overall efficiency. Instead of losing valuable telescope time while changing from imagers to spectrographs or mounting different dispersing elements to change the spectral resolution, a few computer commands sufficed to change modes in a matter of seconds. Improved versions of EFOSC were later developed by Sandro D’Odorico. The detector area had some political sensitivities. A. Lallemand in France had developed an electronic camera that was far superior in performance to photographic plates, but cumbersome to use. After a dozen exposures had been taken, the vacuum seals had to be broken, the exposed emulsions taken out and the camera rebuilt. At the time the 3.6-m was being completed, a Grande Caméra Électronique with a sensitive area of 80 mm diameter had been constructed, and it had been envisaged to use this object of national pride as a detector at the 3.6-m. However, the new solid state detectors that were becoming available in the US were much easier to use and they could communicate directly with a computer. So the installation of the electronic cameras at La Silla would be a major wasted effort. After the initial period up to 1984, in which image tubes, image dissector scanners, reticons and digicons had been used, the quality of the Charge Couple Devices (CCDs) had become so excellent that they became the detector of choice for almost all instruments, be it for imaging or for spectroscopy. Their efficiency in yellow light was coming close to values around 80%, i.e. a factor of fifty better than photographic plates. Infrared astronomy was still in its infancy. The main problem was that at wavelengths longer than 2.5 μm everything, including the atmosphere and the telescope itself, begins to radiate prodigiously at ambient temperatures.

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33

To detect the faint extraterrestrial sources, rapid switching techniques are needed in which the source is compared repeatedly with the “empty” sky. Because the atmosphere is rather variable, the switching between source and background has to be done dozens of times per second. Moreover, to reduce the background due to the infrared instrument itself, the detector and the critical optical elements have to be cooled to temperatures of a few K above absolute zero. Under the leadership of Alan Moorwood some infrared photometers were constructed for the 3.6-m telescope, followed in 1985 by an advanced cryogenic infrared spectrograph based on a small solid state detector array. As a result of the new instrumentation, the ESO 3.6-m / CAT combination was changed from a late-comer of the previous era into a fully up-todate combination. Instead of having to adapt photographic instruments to the new world, the instruments were designed from the beginning for the new detectors. Of course, the CAT remained a small telescope (1.4-m) and only relatively bright stars could be observed. Later, when efficient optical fibers became available, the coudé échelle spectrograph was coupled directly to the 3.6-m telescope and the CAT was closed down. Later additional instrumentation for the 3.6-m telescope would also include a multiple object spectrograph, allowing numerous objects to be observed at the same time, an adaptive optics imager (chapter VII) and a very precise radial velocity meter for planet detection (chapter XV).

The La Silla Telescope Park and its cost At the end of 1971, construction of the 3.6-m telescope was still to begin, but at La Silla smaller telescopes had been springing up like mushrooms: a 1.5-m for spectroscopy, a 1-m for photometry, four 40–60 cm telescopes (partly in cooperation with institutes in the ESO countries) and a 1-m Schmidt telescope for photographing the whole southern sky. While these telescopes could certainly be justified scientifically and politically, the multiplicity of efforts may well have been detrimental for the progress of the main project, the 3.6-m telescope. Instrumentation for these telescopes also represented much effort. Although this was supposed to create valuable experience for the instrumentation of the 3.6-m telescope, hardly anything had been built for the latter when it was completed. Later a 2.2-m and a 1.5-m telescope were also added (Figure II, 3). All these activities came at a considerable cost. Blaauw7) estimates that when the 3.6-m telescope became operational, the (3.6-m) Telescope Project Division had been responsible for only 28% of the cumulative ESO expenditure. While to this should be added the part of the infrastructure needed for the 3.6-m at La Silla, it shows that the cost of the smaller telescopes was far from negligible. Later in the 1986 ESO Annual Report, I presented an

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analysis of the operational cost of the various telescopes at La Silla. Costs incurred in Garching were appropriately apportioned, including those for instrumental development, Visiting Astronomers and administrative overhead. During 1986 the cost for the 3.6-m telescope came to 4.6 M€

Figure II, 3. La Silla in 2003. In the lower part are offices and dormitories. Then come some small telescopes, followed by the 1.5-m, the GPO, the 1-m, the 1.5-m DK, the 2.2-m and the 1-m Schmidt. Higher up are the NTT and the 3.6-m/CAT and to the right the 15-m SEST. Near the bottom is the 15-m inflatable dome for VLT experiments.

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(2004 value), that for all the others (except for the 2.2-m) to 6.3 M€. The 2.2-m is not included here, because its installation was too recent and the cost for its initial instrumentation still high. The light collecting power of each telescope is proportional to the area of the primary mirror; so the cost per m2 is an appropriate indicator of financial efficiency. For the 3.6-m the annual cost amounted to 450 k€/m 2, that for the others on average 780 k€/m2. Thus, the large telescope was cheapest for collecting a given amount of light. While small telescopes may have their uses for special, well focussed projects (see Gamma-Ray Bursts in Chapter XI) or for long time monitoring of interesting objects, in most cases their cost effectiveness is too low to operate them on an isolated site at 10,000 km distance. The economic situation is very different in the vicinity of a university campus where a low cost operation with students is possible. In fact, by now the small telescopes at La Silla have been largely closed down (Table II, 1). Table II, 1. The La Silla Telescopes. Subsequent columns give the diameter, the name or the national partner, the first and last years of use. For some of the smallest telescopes the closing dates are ambiguous, since there was a gradual winding down. The 1.5-m Danish is no longer used by ESO.

2.2-m (MPG) 3.6-m 3.5-m NTT 2.2-m (MPG) 1.5-m 1.5-m DK 1.4-m CAT 1.2-m CH 1.0-m

1983 – 2006? 1976 – 1989 – 1983 – 2006? 1968 – 2002 1979 – 2006? 1981 – 1998 1998 – 1966 – 2001

0.6-m Bochum 1.0-m Schmidt 0.9-m NL 0.6-m Bochum 0.5-m 0.5-m DK 0.4-m GPO

1972 – 1998 1972 – 1998 1979 – 1999 1968 – 1989 1971 – 1997 1969 – 2003 1968 – 1992

15-m SEST

1987 – 2002

In 2004 ESO operated only the 3.6-m, NTT and 2.2-m telescopes. From the budget 2004 it appears that the La Silla operating costs amount to 5.9 M€. Including also the other cost elements, I estimate a total cost of 7 M€ for La Silla, corresponding to 300 k€/m2 for the three telescopes, about a third less than 18 years earlier. So the largest cost reduction at La Silla during the last decade has been due to the closing of the smaller telescopes. These cost figures do not include the capital costs of the construction of the telescope. If we assume the 3.6-m continues to function till 2010, its 78 M€ cost would correspond to some 2.3 M€/year. For the NTT, also with a 33 year lifetime, the corresponding figure would be only 0.7 M€/year. So the capital cost of these telescopes is below the integrated operating cost during their lifetime. Adding the capital and operation costs of the three

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Europe’s quest for the Universe

remaining telescopes, we find that the average cost of one clear night at these telescopes amounts to some 13 k€. In political circles sometimes the complaint has been made that astronomers are good at inaugurating new telescopes, but not at closing old facilities. In fact, when a telescope is to be closed down, it will be said by many astronomers that there is still much useful work that can be done with it. However, this misses the point. The real issues are the cost-to-benefit ratio becoming too high and could the funds needed to operate an older telescope be used more advantageously on newer instruments. From Table II, 1 it is seen that ESO’s record in this respect is rather favorable. From 15 telescopes at La Silla only 5 are still operating, and that number is likely to further diminish. The average lifetime of the 10 obsolete telescopes has been 25 years.

ESO Operations in Chile and in Europe Coming to ESO, I found one other aspect that needed radical change, the operations in Chile. Here there was an astronomical-technical establishment in Santiago far too separated from its raison d’être, the observatory at La Silla. Productivity in the agreeable colonial atmosphere of Santiago was not very high, and in any case it was not ESO’s role to finance an astronomical center there. There was also too large an administrative establishment that found unnecessary roles for itself. So I decided to move almost everyone to La Silla: astronomers, engineers, technicians and much of the administration, leaving only a small office in Santiago. This necessitated the construction of more working and living space on the mountain and the transportation of the staff members living in Santiago or La Serena to La Silla and back at a reasonable frequency. Here the solution involved the airstrip that had been constructed for emergency purposes at Pelícano, in the plain below La Silla. The astronomers in Santiago, who feared the end of their cozy existence, had arranged for one of their friends who owned an airplane to fly me to La Silla so that I could see how easy it would be to stay in Santiago and to pay visits to La Silla when needed. Ironically, this provided the solution in the opposite direction: everything could be moved to La Silla, and the required Santiago-based staff would work at La Silla on a schedule of eight consecutive days of work, followed by six days of rest at home, the transfer being made by air. After some initial grumbling most of the staff rapidly got used to the scheme and many found the six days vacation every two weeks a positive benefit. Thanks to the efforts of Peter de Jonge who managed the difficult transition phase very well, it took less than a year for the new setup to be fully implemented. The whole arrangement contributed much to the efficient functioning of La Silla, also by a much more effective interaction between engineers and astronomers. The administration now was closer to the users of its services,

ESO, La Silla, the 3.6 m Telescope

37

and a smaller number of international staff was far more effective. This arrangement functioned well until ESO developed the Paranal site for the VLT. With operations at two observatory sites a different structure was needed. Managing the mountain was not so simple from the human point of view. The enforced togetherness outside working time gave ample opportunity to exchange and amplify grievances. The mix of international staff and local Chilean staff with different financial conditions also created problems. The basic ESO philosophy was straightforward. In professions for which no suitable staff could be found in Chile, international staff was employed; to find such staff, rather generous payment was required. In professions that could be filled by Chileans, staff was recruited locally and paid according to the scales of the more favorable Chilean enterprises. How to place individual jobs in that scheme remained contentious, and the efforts of the administration to design a detailed job classification on the basis of abstract criteria were not very helpful8). Even though few of the Chilean staff members left voluntarily, because better paymasters were not to be found, their large number on the mountain led to increasing discontent and, finally, to a strike. While this strike led to a number of small measures favorable to the Chilean staff, the long term effect was more negative: to avoid the recurrence of a situation where La Silla could be completely paralyzed, more and more use was made of manpower provided by Chilean companies. By 1978, La Silla was a well functioning observatory with an excellent large telescope much used by visiting astronomers from the member countries and with a slowly growing complement of up-to-date instrumentation. Several smaller telescopes were in routine use (1.5-m, 1-m, Schmidt and some in the 50-cm class). Soon to come was the 1.5-m Danish telescope, with 50% of the time available to ESO. For several years this would be the most solicited telescope after the 3.6-m, but its initial history was not auspicious. In order to save money the 1.5-m mirror was to be polished at an institute in one of the ESO countries. Of course, at the end of the polishing its quality had to be tested, and I was informed by the two astronomers responsible for this that this would be done not by the old outdated methods of ESO, but by marvellous new technology involving interferometers. They declared the mirror to be excellent and it was shipped to Chile. Upon installation in the telescope it was found to have images with 8 arcsecond astigmatism. B. Strömgren at Copenhagen saved the day by raising the necessary funds to bring the mirror back, to have it polished by a reputable professional company and to have it returned to La Silla, albeit with a delay of two years. Upon investigation it turned out that these highly modern testers had assumed in their method that the mirror was axisymmetric! One of them still had the nerve to show up at the next meeting of the IC with a proposal for a novel, rather special instrument for the 3.6-m telescope. Nowadays technical matters concerning large optics are generally better left to optical engineers rather than to scientists.

38

Europe’s quest for the Universe

While ESO operations in Chile were drastically reorganized, important changes also took place in Europe. The Telescope Project division at CERN in Geneva gradually switched its emphasis from work on the telescope to the realization of the instrumentation plan. This also increased the need for a stronger interaction between engineers and scientists. In 1975 a “scientific group” had been established. Its functions were to increase contacts between ESO and the scientists at the member country institutes, to allow young scientists to spend time in the ESO environment, to interact with the engineers, and to perform research especially in areas of European weakness. Very soon this group was also to play a role in data analysis and in particular in image processing which was becoming a prerequisite for the effective use of the new detectors. The first ESO image processing system, IHAP, was developed single-handedly by a young assistant, Frank Middelburg. For a decade, it was used extensively inside and outside of ESO. Following his untimely death and the appearance of a new generation of computers, a new system “MIDAS” gradually took over. A further great change in ESO’s European operation came as a result of the move to Garching. ESO’s first Director General, O. Heckmann, had been the director of the Hamburg observatory at Bergedorf. So looking for some space to start the ESO activities, he found it more or less in his own backyard. When later the telescope project was transferred to the CERN campus, the administration remained behind and the German delegation watched carefully that there would be no change in this. In fact, the Germans hinted in 1973 at an offer to provide space for the ESO headquarters, but the French were reluctant to move the larger part of ESO from Geneva. However, while Germany was paying a large share of the budgets of international scientific organizations (in ESO’s case 1/3), it had no such organizations on its territory. It already had been reluctant to approve CERN II (LEP) in Geneva. Moreover, Switzerland was not a member of ESO and taxes (albeit at a reduced rate) were levied on ESO salaries. And finally Germany was offering to pay for a Headquarters building, while none of the other countries would. At the end of 1975, an agreement was reached that ESO would retain its European headquarters in Germany. Before coming to Geneva I had expected to be able to keep ESO there on the CERN campus. With CERN excellent relations in science and technology were beginning to develop. CERN was an organization run by physicists for physicists and the intellectual environment was most stimulating. Moreover, Geneva is an ideal place for international staff families. However, after six months in office I realized that this would lead to a political disaster endangering the whole organization. So, to the surprise of the staff, I soon became an enthusiastic supporter of the move to Germany. The choice of the location within Germany was left up to me. An appropriate scientific environment was needed, and so the realistic choices were Hamburg, Bonn with the Max-Planck-Institut für Radioastronomie and

ESO, La Silla, the 3.6 m Telescope

39

München with in particular the MPI für Astrophysik (theoretical) and the MPI für Extraterrestrische Physik (largely space research). Both from the scientific and the environmental point of view München appeared the most suitable. The final result was that Reimar Lüst, President of the Max-PlanckGesellschaft, on behalf of the German Government made an offer to construct a 3000 m2 building in Garching to house all ESO’s European activities. After some further political hassles, the ESO Council at its meeting in December 1975 accepted the offer. To celebrate the event, the German delegation took the Council to the Munich opera where it so happened that there was a performance of Verdi’s La Forza del Destino! As ESO’s requirements were further analyzed the building grew to 7000 m2, which Germany generously agreed to finance. In September 1980 the building9) was ready for occupation (Figure II, 4) and the staff was transferred, though about one third chose to quit and remain in Geneva. This led to substantial delays in the completion of instruments. New staff had to be attracted and some lost experience regained. However, the effects of this shake up were perhaps not entirely negative. Technologically in future projects a break with the past was necessary. With the partial replacement of the staff this was much easier to achieve. There was one more important transaction with the MPG which concerned the 2.2-m telescope. In the sixties the MPI für Astronomie had been founded to operate observatories equipped with one 3.5-m and two 2.2-m telescopes for use by the whole German community. The idea had been to

Figure II, 4. The elegant ESO headquarters building in Garching near Munich designed by the architects Fehling and Gogel. Since this photograph was taken, the building has been further enlarged.

40

Europe’s quest for the Universe

place these at Calar Alto in Spain and on the Gamsberg in South West Africa (Namibia). Because of political problems with the latter site, the 3.5-m and one of the 2.2-m telescopes had been placed at Calar Alto, while the remaining 2.2-m was stored awaiting better days. However, the political situation remained unchanged and having an expensive telescope lying about unused and ageing became an embarrassment. Hence an approach from the President of the MPG to discuss the possibility of placing it at La Silla. Since the attitudes of the MPIA and ESO at the time were rather different, it seemed clear that this could only work if ESO would gain full control of the telescope and its modernization. After some difficult negotiations an agreement was reached under which ESO would receive the telescope on long term loan and have the exclusive responsibility for its upgrading and operation. In return the MPIA would receive 25% of the observing time. This provided an excellent 2.2-m telescope at La Silla, suitable for programs that did not require the 3.6-m, but for which the 1.5-m Danish was inadequate. After the telescope began to function successfully the relationship with the MPIA became smooth and cordial.

Other European 4-m Class Telescope Projects In 1961 the UK had definitely abandoned participation in ESO and decided to have a joint project with Australia for a 3.9-m telescope. The telescope was to be as much as possible a copy of the Kitt Peak (Arizona) 150-inch national US telescope. It was finally completed in 1974 and placed on the Siding Springs site near Coonabarabran (NSW) which belonged to the Australian National University. While this site was free from the light pollution that had plagued the ANU observatory at Mt. Stromlo near Canberra, it was only moderately suitable because of its low altitude. However, the excellent quality of the telescope, and especially of its computer control system, made up for this drawback, and it has been very productive. Now that the UK has joined ESO, it is expected that its participation in the AAT will diminish. The UK – later joined by the Netherlands with 20% participation – also developed major facilities on La Palma in the Canary Islands, where it now operates 4.5-m and 2.5-m telescopes. The site is excellent for optical telescopes, but was considered not optimal for the infrared. So, a 3.8-m IR telescope was also built, the UKIRT, at 4200 m on Mauna Kea (Hawaii). It is now also part of the UK – NL cooperation. Due to the high altitude atmospheric transmission is very favorable and excellent results were obtained even in the 300 μm window. Also the French were anxious to construct a national telescope. Site tests in France and southern Spain gave unsatisfactory results. So they joined (initially at 42.5%) the Canadians and the University of Hawaii in the

ESO, La Silla, the 3.6 m Telescope

41

construction of a 3.6-m telescope on Mauna Kea, a most fortunate choice. In the beginning the telescope suffered from an excess of instrumentation. This led to frequent instrument changes. Since it takes some time before a newly installed instrument functions optimally, this resulted in a significant loss of effective telescope time. After this had been corrected, the CFHT became very successful, in part because of its excellent site. Today it is equipped with a 400 Megapixel CCD camera built in Saclay (F) which allows more than one square degree of the sky to be imaged all at once with high resolution and sensitivity. Italian plans for a national telescope led to the selection of a site near Castel Grande in southern Italy. However, thereafter the project stalled. Renewed activity began when Italy joined ESO and the plan was made to model the telescope on the NTT. It took, however, till 1999 before the 3.5m Galileo Telescope became operational at La Palma, the inferior Italian site having been largely abandoned in the meantime. In Germany it had been difficult to find a suitable organisation to take charge of a major observatory. Because the universities belonged to the numerous state governments they did not have the capacity for this. Finally, the German government funded telescopes to be built by Zeiss, and the MaxPlanck-Gesellschaft founded the Institut für Astronomie in Heidelberg, which opened in 1969 and which was to operate the telescopes. Site surveys in Greece and southern Spain resulted in the selection of Calar Alto near Almeria, where there are now 3.5-m and 2.2-m telescopes, as well as some smaller ones. Unfortunately, the quality of the site is not optimal. From 2005 onwards Calar Alto will become a joint venture of the MPG and the Spanish Research Council. Adding it all up (Table II, 2), we see that Europe has some seven 4-m class telescopes at its disposal, about the same number as the U.S. A smaller European venture needs to be mentioned – the 2.5-m Nordic Optical Telescope (NOT, 1989) at La Palma. This joint venture of Denmark, Finland, Norway and Sweden, later joined by Iceland, has been very successful because of the excellent image quality.

Europe’s quest for the Universe

42

Table II, 2. The 3.5–6 meter Astronomical Telescopes in the World.

Year

+

Country/ Diameter Organisation (m)

1949

USA

5.1+

1973

USA

4.0+

1974

UK/Australia

3.9+

1975

USA

4.0+

1976

Russia

6.0+

1976

ESO

3.6+

1978

USA

4.5+

1979

UK/NL (20%)

3.8+

1979 1985

Can/F/USA D (MPG)

3.6+ 3.5+

1987

UK/NL (20%)

4.2+

1989 1994

ESO USA

3.5+ 3.5+

1995 1999 2004

USA I USA/Brazil/Chile

3.5+ 3.5+ 4.1+

Alt Azimuth mounting.

Location Mt. Palomar, California Kitt Peak, Arizona Siding Springs, Australia Co. Tololo, Chile Zelentchuk, Caucasus Co. La Silla, Chile Mt. Hopkins, Arizona Mauna Kea, Hawaii Mauna Kea Calar Alto, Spain La Palma, Canaries Co. La Silla Apache Pt., New Mexico Kitt Peak La Palma Co. Pachon, Chile

Altitude (m)

Usual Name

1700

Hale

2100

Mayall

1100

AAT

2200

Blanco

2000 2400 2400

MMT

4200

UKIRT

4200 2200

CFHT

2400

W. Herschel

2400 2800

NTT ARC

2100 2400 2700

WIYN Galileo SOAR

III. Origin of the VLT Project; The NTT

Part of the task is done and part remains. Here let us rest and moor our boat. Ovidius1)

By 1978 the 3.6-m telescope had been installed at La Silla, visiting astronomers were regularly observing there, the instrumentation plan was being executed and the ESO organization functioned smoothly. The member states contributed 32.5 MDM (32 M€ 2004 value) annually to the organization and some expected that a reduction would be possible, since the main aim had been achieved. But though the progress made was very satisfactory, there was still much in the Universe that was out of reach even with a 3.6-m telescope: galaxies at large redshifts essential to cosmology, the chemical composition of stars far away from the disk of our Galaxy and many others could be mentioned. Still larger telescopes would therefore be needed in the future to analyze problems that could be only dimly perceived with telescopes in the 3.6-m class. And while it was most satisfying that Europe now had its own large telescopes and that its scientists could begin to compete at world level, it was clear that this happy state of affairs could not last forever. If ESO did not look for future opportunities others certainly would, and European scientists would soon again be at a competitive disadvantage. The situation is very similar to that in particle physics. To create new and heavy particles or to search for rare decay modes, ever higher energies or more intense beams are needed. The result has been that accelerators have become bigger and technologically and financially more challenging. This is not a quest for bigness per se, but the unfortunate fact that the exploration of new areas tends to be ever more demanding. In exactly the same way the observation of ever fainter objects requires telescopes of increasing flux collecting power. Thus, in California the 60-inch telescope (1908) was succeeded by the 100-inch (1917) and the 200-inch (1949) telescopes. Each of these allowed major new discoveries to be made.

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Europe’s quest for the Universe

Construction of the 200-inch telescope was followed by a period of stagnation in telescope sizes until the U.S.S.R. 6-m telescope was completed in 1976. However, its mirror was so massive that thermal equilibrium with the surrounding air could not easily be established, while its long focal length required a very large dome. Both had negative effects on the image quality. The other large telescopes constructed in the seventies and eighties all were in the 4-m class. Nevertheless, much progress was made in the detection of fainter objects. The reason was that the efficiency of detectors had increased spectacularly. The light detecting capability of a telescope is proportional to the total light collected multiplied by the fraction that is actually detected. Thus, a 10-m telescope equipped with a detector with 1% efficiency detects as much light – as many photons – as a 1-m telescope with a detector that has 100% efficiency. The photographic plates used with the 60-inch telescope probably had an efficiency of no more than 1% (and because of reciprocity failure probably even less for very faint objects). With present day CCD detectors efficiencies of up to 80% have been attained. Thus, in a global sense, the 60-inch telescope equipped with today’s CCD is equal to a 14-m telescope with the photographic plates of a century ago. Of course, this analysis is too simple-minded, and other factors have to be considered in the comparison. But it is clear that while telescope size remained more or less stationary, the effective light gathering power increased very substantially. Now that detectors have reached efficiencies close to 100%, no further progress in light gathering ability is possible without increasing the telescope size - at least when direct imaging is considered. Other reasons to increase telescope size relate to angular resolution, which we shall consider later. It was clear then that the construction of a telescope larger than the 3.6-m would be advantageous from a scientific point of view. It was also important to start considering such a possibility rather soon. Much technological development would be needed. Moreover, if there would be no new project, the ESO budget would decline; politically it is much easier, especially in an international organization, to maintain a constant budget than to have one that first goes down and then has to be increased later. And finally the Americans were not sitting still, with first ideas about telescopes of up to 25 m diameter being discussed. A large telescope does not necessarily have to be made as one unit (Figure III, 1). One can also build an array of telescopes and combine their output optically or the output of their detectors digitally. In fact, optical combination was already being implemented in the multi-mirror telescope (MMT), a set of six 1.8-m telescopes of the University of Arizona. The light gathering power was therefore nominally that of a 4.5-m telescope, though losses in the reflections of the combining mirrors made it somewhat less. At the MMT2) the six telescopes were located in a common mounting, but in principle also the light of an array of fully independent telescopes could be combined at a common focus, though the combining optics would be more

Origin of the VLT Project; The NTT

a

b

45

c

Figure III, 1. Three ways to build a large telescope. a – A segmented mirror composed of a number of hexagonal (or otherwise shaped) appropriately figured segments which are accurately supported so that the overall surface has the required form. The individual segments should be thick enough to be rigid, but the overall thickness to diameter ratio, and therefore the weight, remains low. b – A multimirror telescope in which a number of mirrors are placed in a common mounting and the light is combined optically. c – An array telescope in which the mirrors have separate mounts. Again, the light may be combined optically. A solution of type a has been implemented in the two 10-m Keck telescopes in the US and in the Spanish 10-m Grantecan, solution b (with only two mirrors) in the 2 × 8 m LBT (US, D, I) and solution c in the 4 × 8 m ESO VLT.

complex. Arrays of this type are required for interferometry, and at the time an array of two small telescopes had been constructed by A. Labeyrie3) in France, while large arrays of 1-2 m class telescopes were being advocated by M. Disney4) in the UK. So what could be the next ESO telescope project? It seemed to me that it should represent a large step compared to what had been done before; it was no longer a question of catching up with the rest of the world, but of taking the lead. Otherwise it would be difficult to obtain the necessary support. A 16-m telescope might be within reach or, more probably, an array of telescopes with a total collecting area equal to that of a 16-m. The reasoning was simple. ESO had built a very complex 3.6-m telescope at a cost of some 68 MDM or 78 M€ (2004 value). With an alt-azimuth mounting, a very simple building, no exchangeable parts and a highly simplified coudé focus, a cost of 20–30 MDM would appear not unreasonable, and newer technology might well allow the lower figure. In the preceding decade, the European countries had invested in total more than 200 MDM in large telescope projects. Hence, with a comparable investment in a large ESO project some ten 3.6-m telescopes could be acquired. But if one constructs a large number of identical objects, the unit price goes down. With 10 identical objects the cost might be about halved. So then some twenty 3.6-m telescopes could be financed, corresponding to the area of a 16-m telescope. This estimate

46

Europe’s quest for the Universe

neglected the problems associated with the combination of the light from the telescopes and the cost of the instrumentation. But it showed that it was not an excessively ambitious aim to build a 16-m equivalent telescope. I made the first proposal to do so at the ESO conference “Optical Telescopes of the Future” held in Geneva, December 19775). At this conference many interesting ideas were presented which also helped to further crystallize our own. Of course, the model of twenty 3.6-m telescopes was not a particularly attractive option, but it could easily be costed. A more ambitious project with larger unit telescopes was called for, but needed more analysis. At the time I listed just five illustrative examples of what such a telescope would do. They were the following: 1. Abundances of elements in globular cluster stars. Composition variations were believed to be due to differences in the elemental abundances of the gaseous medium from which such stars formed, but since only evolved stars could be observed effects of stellar evolution could also play a role. But adequate analysis of unevolved stars was hardly possible because they were too faint for 4-m class telescopes. Actually the VLT has been used extensively to study the abundances of cluster and halo stars. 2. The motion of globular clusters in other galaxies informs us about their masses and about their “dark matter” content. 3. Cosmological studies involving faint galaxies and quasars would be of much importance. While the faintest objects might best be detected with the Hubble Space Telescope, more detailed spectroscopy of somewhat brighter objects would be the domain of the 16-m telescope. This complementarity has been very much in evidence with the VLT. 4. Correlative optical studies of radio and X-ray sources. In fact, extremely faint counterparts to X-ray sources have been found at the limit of what the VLT can observe. 5. High time resolution photometry of X-ray sources. Today one would have replaced this by observations of remote supernovae to determine the structure of the Universe. Of course, many other topics could have been listed, in particular also in the infrared. To me it seemed highly premature to go in one step to a 16-m telescope. ESO had constructed a moderately satisfactory 3.6-m. The USSR 6-m telescope was the largest in the world. It was a heavy monster. Just scaling up these telescopes to 16-m was not going to work. The step to 16 m was too large. If something would go wrong, the loss would be total. On the other hand, the optical combination of a large number of small telescopes would lead to important light losses, which could defeat the aim of efficient photon collection. And if all of these would be individually instrumented, the cost of the instruments might become a large part of the total. While such an array might yield high angular resolution on bright objects when used in an interferometric mode, for the imaging of very faint objects it would be far from

Origin of the VLT Project; The NTT

47

optimal. With galaxies and quasars at large redshifts and distant halo stars looming as the dominant scientific topics of the future, this was an essential point. In a very general way an array of 8-m telescopes would have several advantages. Each of these would represent a significant advance in telescope technology and scientific capability compared to the 3.6-m telescope. With such an array one would have the choice to use the 8-m telescopes, when required, as an array, but they could also be used as four large telescopes for different projects and perhaps also be instrumented differently. This argument was slightly delicate, since if the integrated array concept were too much deemphasized very soon funding for only one telescope of 8 m would be obtainable. And if the array concept would turn out to be successful, additional possibilities would open up – like interferometry. Immediately after the conference I asked our technical staff to make a first study of three options: one 16-m telescope and arrays of four 8-m and sixteen 4-m telescopes. All three would have the same collecting area. With this specification I had little doubt that the result would be that one would see the disadvantages of the two extremes and therefore settle on the intermediate solution. In fact, the solution with 4-m telescopes did not find much favor with anyone. It would require complex and expensive combining optics if the telescopes would be coupled optically and a large amount of instrumentation if each telescope would be instrumented separately and the outputs combined electronically. For the infrared larger unit telescopes would have significant advantages. Some in the infrared community favored one 16-m as this could have an advantage in angular resolution, but there was no unanimity about this. There was also the suggestion to place the 16m telescope on a very high site with low atmospheric water vapor which absorbs IR radiation and, because of the physiological problems associated with this, to have it operated by technicians rather than by astronomers. Apparently some engineers did not think much of the endurance of their astronomical brethren! All these studies had been done with an inadequate level of effort, since most of the staff was very busy with work on the 3.6-m and CAT telescopes and their instrumentation. Moreover, ESO’s departure from Geneva was approaching, part of the engineering staff were looking for alternative employment, and replacements still had to be found. Not surprisingly, there were quite a few astronomers who had other ideas of what to do when money would become available. This made it dangerous to push the project too much before proper technical studies had been made. So, on the one hand, it was important to keep the project alive so that it became part of the astronomical consciousness in Europe, but, on the other hand, not to stress it too much and too prematurely so that not too much opposition would arise. The opportunity to build the New Technology Telescope with the entry fees of two new member countries facilitated this and allowed the required technologies to be developed.

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Europe’s quest for the Universe

Italy and Switzerland In 1980 ESO’s horizons were suddenly enlarged and wonderful opportunities to push telescope development arose. For some years discussions had been taking place with Italy and Switzerland concerning eventual membership in ESO. The great majority of Swiss astronomers had been interested in joining ESO. The Geneva Observatory had obtained permission to place a 40cm photometric telescope at La Silla, and its director Marcel Golay pushed very hard for membership. From ESO’s side it had been noted that the agreement to place that telescope at La Silla was made in the anticipation that full membership would follow. Also in Basel much support was given. However, the well known solar astronomer M. Waldmeier in Zurich was strongly opposed and held up the matter for a long time. So the Swiss authorities turned down the proposal. When it became clear that Italy was going to join, it was evident that ESO would be the European organization in astronomy and the Swiss proposal was successfully revived. According to the convention, new member countries would have to pay an “entrance fee” for their share in the investments made by the other countries. The negotiation about the sum to be paid was essentially political, but had to be justified in terms of the assets of the organization and the depreciation thereof. A sum of DM 6,000,000 was asked for, which was not quite acceptable for the Swiss. Finally, I proposed a compromise on the basis of CHF 5,000,000, which at the time was some 10% less than the DM amount, but by the time it was paid in 1982 was actually slightly more. The negotiations with Italy had been going on for some years, pushed forward by Franco Pacini and Giancarlo Setti. Between the two of them they covered the most essential parts of the Italian political spectrum in parliament. The frequent changes in government had made it difficult to progress; in fact, some five subsequent ministers or state secretaries had been involved! The decisive push came when Consigliere U. Vattani, at the time the Chef de Cabinet of Research Minister Scalia, took a personal interest in the matter. A final negotiation took place in Taormina where after some discussion our positions were still rather far apart concerning the entrance fee. When Minister Scalia arrived and was informed of the situation, he said: “My region (Sicily) may be a poor region, but when we arrive at such a situation, we usually divide the difference in two” – and so it was done, somewhat to the distress of Cons. Vattani who believed that ESO ultimately would have been satisfied with less. An interesting aspect was that 3 MDM in money would be replaced, if technically feasible, by a slice of the 3.5-m disk of fused silica that the Italians had acquired earlier for their national project. Since ESO was now planning to build a thin mirror telescope and the Italians a copy of this, in principle it seemed possible to slice that disk in two. After the agreement had been reached, some speeches were held at dinner, and it turned out that the

Origin of the VLT Project; The NTT

49

political people believed that the disk would be cut into two half circular pieces! Later it appeared that the distribution of bubbles in the disk made the slicing impossible. However, by that time the political negotiations had produced a result that was irreversible, and this did not create further problems. In Italy it may take many years to obtain parliamentary ratification of international agreements. However, Consigliere Vattani, by that time chef de cabinet of the prime minister, succeeded to place it on a fast track. By 1981 Italy was a de facto member and the year thereafter all formalities had been completed. Also in 1982 the Swiss parliament ratified the ESO Convention, although some deputies complained that ESO membership was funded, while a proposal for support of the Rhaeto-Romanic language was not. According to the ESO Convention (article VII; 4), the entrance fees paid by new member states should be used to reduce the contributions of the other member states, unless the Council would unanimously decide otherwise. Observing time was already in short supply, and with an increase of the user community by some 35%, the situation would become untenable. Council therefore readily agreed to my proposal to use the entrance fees to build a simple 3.5-m New Technology Telescope (NTT) to improve the situation. In 1982 the budget for this was set at 24 MDM. Upon completion of the NTT, a surplus of 3.4 MDM remained, which could be used to instrument the telescope. So the cost of the NTT amounted to 21 MDM or some 18 M€ (2004 value). If we include the uncertain in-house personnel costs, the total becomes 25 M€ (2004), or only 32% of the cost of the 3.6-m telescope, a remarkable progress in some 13 years. The annual contribution of the ESO member countries had remained fixed from 1976-1981 at 32.5 MDM. By 1982 this constant level would have represented a loss of 31% in real terms. The adhesion of the new countries made it possible to remedy the situation in a painless way. The contribution level in 1982 was raised to 40 MDM. Through partial inflation correction it became 49.5 MDM (equivalent to 38 M€, 2004 value) six years later. A rapid increase followed to pay for the VLT and thereafter for ALMA. In 2004 it amounted to 100 M€. While the new member countries were important in increasing the financial resources of ESO and allowing a new telescope project to be started, perhaps the most significant aspect was that it provided a new political legitimacy to ESO as the organization for astronomy in Europe. If new countries bothered to join, the organization must have a certain importance, and a whole new dynamics arose which gave it the necessary momentum and confidence to later start the VLT project. However, at the time that the NTT was decided, Council considerably watered down the resolution I had proposed in which the NTT was stated to be the prototype of the VLT. Anything that looked like a commitment to the VLT was still far off.

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The NTT When in 1980 it seemed that Italy and Switzerland would join ESO, it was essential to have a telescope project ready to have a specific destination for the entrance fees. While this did not have to be a fully developed design, it should at least give a believable cost estimate. Since the available time at the 3.6-m telescope would now be shared with an enlarged community, it should also be realizable quickly so as to enlarge the pool of observing time. With a slice of the Italian mirror being part of the deal, the diameter was fixed at 3.5 m. And even though officially there was no connection to the VLT, the new telescope should serve as a demonstration of various technologies which later could make the case for that project more convincing and show that it could be constructed at an acceptable cost. Thus, cost and speed became the dominant design criteria for the NTT. The 3.6-m telescope had had a high cost because it was mechanically awkward with its polar mount and multiple focus options based on exchangeable top units, because it was heavy and because it was enclosed in a very large building, which accounted for some 40% of the total cost. The building was 30 m in diameter. It was 30 m high, with a 30 m diameter dome on top, because it had been believed that the atmospheric turbulence would be reduced far above the ground. However, it was beginning to be clear that the large volume of the telescope enclosure did much harm with turbulence created by warm areas in the building degrading observing conditions. At Las Campanas, 50 km from La Silla, the Carnegie Institution had built a 2.5-m telescope and because of its limited budget it had been placed in a low building. No harmful effects were in evidence. So to bring down the cost of the NTT, the general guidelines were simplicity, weight reduction and a small building volume. More specifically the following items were considered important6): (1) The NTT would have an alt-azimuth mounting. The more straightforward mechanical structure would weigh less and have lower cost. (2) The alt-azimuth design provides, rather naturally, two Nasmyth foci where heavy instruments may be placed on platforms rotating with the telescope (Figure III, 2). The light is deflected by a flat mirror at an angle of 45˚ with respect to the optical axis (Figure II, 1). To go from one Nasmyth focus to the other the mirror must be turned by 180°, a relatively simple operation. As a result, one may switch very rapidly from an instrument at one focus to another at the other focus. This makes instrument changes very much less cumbersome than at the Cassegrain focus of the 3.6-m, where one instrument has to be removed to make place for another, which in practice cannot be done during the night. It is also considerably more efficient than the complicated coudé setup which has additional reflections in most versions and a small field of view. The Nasmyth flat mirror takes away some 15% of the light, and so there

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Figure III, 2. Model of the NTT. The telescope rotates around a vertical axis (the azimuth axis) on a large bearing; the telescope tube can rotate from horizontal to vertical on the elevation axis. The housing of the direct drive motors is visible on this axis. The light of a celestial object first falls on the 3.5-m mirror at the bottom of the tube, returns to the secondary at the upper end and then is directed by the third, flat, Nasmyth mirror sideways through the elevation axis to either the left or the right Nasmyth focus where instrumentation may be placed. In this model, the Nasmyth platforms have not yet been mounted. The black baffle shields the Nasmyth mirror from stray light.

were some wishes to also have a Cassegrain focus. However, this would have required a mechanism to take the flat mirror out of the optical path and a prolongation of the fork to accommodate instrumentation. This would have added a significant cost to which I could not agree. (3) The length of the telescope tube is largely determined by the focal length of the primary mirror. A low focal ratio (focal length / mirror diameter) allows a short tube. This reduces the size of the enclosure housing the telescope. However, a mirror of low focal ratio (usually called a “fast” mirror) was more expensive to manufacture , and in general the optical tolerances are tighter if the mirror is very fast. From such considerations an optimal focal ratio 27% smaller than that for the 3.6-m was adopted.

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As a result of this and of the compact alt-az design, the mean diameter of the enclosure was 19 m, instead of 30 m for the 3.6-m telescope. (4) The height of the building would be much smaller than in the case of the 3.6-m telescope (Figure III, 3). The top of the dome of the latter was more than 40 m above the ground. The highest point of the enclosure of the NTT was only at 17 m, and its total volume only one fifth of that for the 3.6 m. (5) Since the telescope rotates around the azimuth axis, all connections between it and a stationary building (cables, pipes, etc.) have to be made in a rather special way. At the MMT of the University of Arizona it had therefore been decided to let the building rotate with the telescope, and this same solution was adopted for the NTT. This had another major advantage. Since with respect to the building the telescope moved only in elevation, walls could be placed on either side. This allowed all heat sources to be away from the telescope and thereby to eliminate much of the dome turbulence that had plagued the 3.6-m. In addition, no classical dome was needed and the telescope enclosure could be designed in a more cost effective way. (6) The telescope drive also would contain a major innovation – the use of large torque motors. Keeping a telescope pointed to the same point in the sky to within a fraction of an arcsecond requires a very finely tuned drive system. This had generally been achieved in large telescopes by a set of gears which diminished the requirements on the precision of the motors by a substantial factor. However, in the meantime, very large torque motors had been manufactured in the USA, which could be directly

Figure III, 3. The relative sizes of the enclosures of the 3.6-m (black), the VLT 8.2-m unit telescope (green) and the 3.5-m NTT (red). Since the latter two are not circularly symmetric, they would have somewhat different shapes when seen from different directions.

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mounted on the telescope axes. In fact, at the 1.4-m CAT such motors were already in use and functioned well. However, much bigger motors were required to steer the larger mass of a 3.5-m telescope. The great advantage is that the backlash in the gears is eliminated and the overall control system is simplified. 7) The greatest innovation would be the use of active optics, pioneered by Ray Wilson at ESO7). In conventional telescopes mirror deformations under the changing orientation of gravitational forces had been minimized by making the mirror thick – typically with thickness / diameter about equal to 1/6. Such a mirror is heavy – of the order of 10 tons for a 3.5-m mirror. But even a thick, heavy, stiff mirror will experience serious deformations due to gravity when the telescope moves. The mirror is therefore placed in a “mirror cell” in which it is supported by an appropriate set of levers that should compensate the varying gravitational forces. If the mirror is thick enough a rather simple setup is sufficient. For large telescopes the weight of a thick mirror becomes prohibitive, and other solutions are needed. Active optics holds the key. If a mirror is deformed from its perfect shape, the image of a star becomes distorted too. With an “image analyzer” the nature of the deformation may be ascertained. By exerting appropriate forces on the mirror the deformation may be removed and the image quality restored (Figure III, 4).

Figure III, 4. Active Optics. The light of a star is reflected first by the primary mirror supported by a large number of motorized levers which determine its shape. Subsequently, it is reflected by the secondary mirror, the position of which can also be adjusted by motors, and finally brought to the focus by a third, flat, mirror. Some of the light is analyzed by a wavefront sensor coupled to a computer which determines the corrections to be made to the shape of the primary and the position of the secondary for optimal imaging and which sends the appropriate instructions to the motors.

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The image analyzer may, for example, be based on a “Hartmann screen”, a screen with a regular array of holes placed in the parallel beam or closer to the focal plane. When a photographic plate is placed some distance from the focal plane, a set of spots is seen. If the mirror is distorted by large scale deformations, the positional pattern of the spots is also deformed. When the photographic plate is replaced by a solid state detector (CCD) with the readout directly fed into the computer, the spot positions may be determined on line. The mirror is supported by motorized levers or pistons that exert forces on the mirror (Figure III, 5). After having calibrated the relation between the magnitudes of these forces and the deformations of the mirror, it becomes a simple matter to have the computer translate its knowledge of the deformation of the mirror into instructions to the motors so that the required forces are applied to undo the deformation.

Figure III, 5. Support system for a 1-m mirror active optics experiment at ESO. Each support is adjusted by a motor which in turn is computer controlled. The instructions of the computer are based on the measurements of the wavefront sensor which determines the corrections needed to the shape of the mirror to compensate for its deformations.

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To control the 3.5 m diameter mirror of the NTT 78 axial levers are required (Figure III, 6) and for the 8.2 m VLT mirrors 150, but enough computing power is nowadays available to control these appropriately. In the same way also the position of the secondary mirror in a Cassegrain system may be controlled. Since a sufficiently bright reference star may not be available near to the object, in practice the active optics measurements are made only from time to time and the levers adjusted in between by extrapolation based on previous experience. Active optics also relaxes the specifications for mirror polishing and thereby may reduce cost and allow the correction of errors. A thick mirror has to be polished to high specifications to avoid image deformation. With a thin actively controlled mirror errors in shape can be partly corrected. The problems of the Hubble Space Telescope (wrong focus of the primary) could have been corrected remotely if it had had an active optics system. Of course, small scale roughness cannot be corrected. With a system of levers only errors on at least the scale of the separation between levers can be dealt with.

Figure III, 6. The main mirror cell of the NTT. The 78 actuators are placed in four rings. Above the mirror cell is the main massive support structure between the two wheels that steer the telescope in elevation. The support structure for the secondary mirror is partially visible at the top.

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With active optics the primary mirror could be thin. If the mirror weight is smaller, the telescope tube can also be less heavy, and finally the whole telescope will have less weight and thereby less cost. The concept seemed very promising, but it had not yet been tried in a real telescope. I therefore concluded that one should not go to the extremely thin mirror that this technology allowed, but keep the mirror thick enough that even with the classical support systems acceptable images would be obtainable. After all, it would be a disaster for the prospects of the VLT if the NTT would not function correctly within a reasonable time. At the same time, the 3.5-m mirror should be thin enough to test the active optics scheme. The aspect ratio (thickness/diameter) was finally set at 1:15 to be compared with 1:6 for the 3.6-m telescope. As a result, the weight was only 40% of that of the latter. A very preliminary mechanical design by Wolfgang Richter, based on an altazimuth mounting, sufficed to estimate its cost. As soon as the Italian and Swiss parliaments had ratified the ESO Convention, a small NTT project group was set up at ESO. Initially it was headed by Ray Wilson who had developed the active optics concepts. However, he did not find project management very congenial and at his request was succeeded by Massimo Tarenghi who later also would successfully manage the VLT. This led to a tight management which, though essential for the project, did not please everyone. Evidently during the conceptual phase it is best to “let a thousand flowers bloom”, but once contracts have been concluded, changes should be infrequent and deadlines should be met. If not, the cost rapidly escalates. While ESO had made the conceptual design, a detailed design as the basis for a construction tender had to be done and after the move from Geneva ESO’s manpower was inadequate to do this in-house. A tender was given out and several offers were received; included were a very satisfactory offer by Krupp-MAN that was selected, and a technically totally inadequate offer from a firm in another country at only 40% of the price. This led to some political upheaval, and it took much effort to have the contract approved by the ESO Finance Committee. While price is a relatively simple criterion to compare contracts, quality is necessarily more ambiguous. Another problem was how to acquire a disk for the mirror. It had been found that the idea of slicing the Italian disk, which had played a very useful role in the political discussions, was not feasible. Initial contacts with Schott, the maker of Zerodur, did not yield a satisfactory price. So it was decided to talk in Moscow about a possible disk in astrosital, another low expansion material. The concern here was that this would have too much internal tension since it was to be cut out of pieces of a cracked 6-m disk. Discussions took place on how to test such a disk in East Germany, since gaining full access to the factory in Moscow proved difficult. I had expected that Schott would not wish to have competition from astrosital in western markets. In fact, rather soon a much more satisfactory offer for a Zerodur disk was made by Schott and accepted by ESO.

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Some ideas had also been developed about mirrors in aluminum or steel, and some experimental studies were being performed at ESO. These experiments were continued for some time in case problems would be encountered with the acquisition of mirror blanks for the VLT, but for the NTT it seemed preferable to stay with the proven Zerodur. Though this was disappointing to the optical engineers who looked forward to an interesting innovative mirror experiment, the approach of the VLT decision necessitated the most rapid completion of a system that was guaranteed to work. In 1986 the Zerodur disk was delivered and sent to Zeiss for polishing. By mid-1988 the polishing had been completed and a test of the complete active optics system was made, which showed the high quality of the mirror and the successful implementation of the active optics concept. Later that year the mirror joined the mechanics (Figure III, 7a) and enclosure erected at La Silla (Figure III, 7b).

Figure III, 7a (left). The NTT. Below the floor is the azimuth bearing and the base of the fork-like structure. Behind the walls on the sides are the Nasmyth platforms. So the telescope is shielded from most sources of heat which could cause turbulence in the air in or above the tube of the telescope and degrade the image quality. In the upper ring is the support structure for the secondary mirror whose position is computer controlled. In the square structure is the support for the Nasmyth mirror which can send the light to the left or to the right through the elevation axis. Below this the primary mirror and its support structure are seen. Figure III, 7b (right). The enclosure of the NTT. The telescope rotates in azimuth on a high precision hydrostatic bearing, while the enclosure rotates along on a simpler 7m roller bearing. The metallic structure of the enclosure is of much lower cost than a conventional building plus dome.

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Finally, on the night of 22 March 1989 the first direct CCD images were taken; by luck that night also the atmospheric turbulence was low and the images were probably the best ever taken by a ground-based telescope. The successful completion of the NTT showed that ESO now had the engineering competence for innovation in telescope technology. While the 3.6 m telescope had been one of the last of the previous generation of large telescopes, the NTT was the first of a new generation of telescopes based on active optics, new control concepts and rationally designed enclosures which suppressed dome seeing. The success of the NTT gave the ESO countries the confidence that the VLT had become a realizable dream. One last question remained to be settled when the telescope mechanics were shipped to Chile. Where should the NTT be placed? By 1986 the excellent qualities of the Paranal site had become clear, though the site testing was far from terminated. While the Paranal peak itself had been reserved for the VLT, there was a small hill somewhat lower and usually upwind from Paranal that would provide an excellent place. Some tests were made there which indicated that the quality of what became to be known as “NTT hill” could be expected to be excellent. While I was very much tempted to place the NTT there, the total absence of any infrastructure at Paranal would be difficult. Since the NTT was a highly innovative telescope, it was not excluded that there would be problems that would be much easier to solve at La Silla. The risk was too great, and serious problems with the NTT would have endangered the VLT. So, the NTT was placed at La Silla. If the NTT had been in the Paranal area, subsequent considerations about the future of La Silla and its relation to Paranal might have been much simplified.

IV. Technological, Financial and Scientific Planning of the VLT

Ein bis dahin unbekannter, beinahe politisch zu nennender Gemeingeist hat eine Organisation entwickelt, die auf ein wissenschaftlich ganz neues Niveau hinstrebt. Otto Heckmann1)

On 1 September 1980 ESO’s scientific-technical establishments moved from CERN, Geneva, to Garching near Munich. Nearly half of the technical staff did not follow ESO and so their personal priorities became rather different from those of ESO. Moreover, the staff who moved to Garching had to get settled there, contribute to the recruitment of new staff and introduce the newcomers to the various projects. As a result, the move delayed ESO’s projects by a year. By the time the new ESO establishment was inaugurated on 5 May 1981 by the President of the Federal Republic of Germany, most of the scars from the rupture had been removed and the organization again began to function normally. There were at that time still several major instrumental projects for the 3.6-m telescope at La Silla which had to be completed urgently if that telescope were to be competitive. As a consequence, the technical staff hardly could devote much time to projects for the more distant future, including the VLT. Moreover, the development of the NTT already stressed the available manpower. Still advances could be made by involving a number of scientists from the ESO countries in discussions of some critical issues. I therefore set up a “VLT Study Group” under the chairmanship of Jean Pierre Swings of Liège, with a core membership of about a dozen scientists and engineers2) and with additional contributions by a number of interested persons. About twenty meetings of the Study Group took place. This led to a workshop with 46 participants, two thirds from institutes in the ESO countries and the others

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from ESO, held in Cargèse, Corsica, 16-19 May 19832). Among the conclusions reached there were a reaffirmation of the 16-m equivalent diameter, a strong inclination towards an array of three or four telescopes with monolithic mirrors, and a lukewarm emphasis on interferometry with the large telescopes. The latter resulted from studies by Pierre Léna3) and François Roddier4) which indicated that the gain in limiting magnitude with larger telescopes was rather small due to the effects of the earth’s atmosphere. For interferometry more numerous smaller movable telescopes seemed preferable to the large fixed ones. This created a dangerous situation from the political point of view. In particular for the French, interferometry was a high priority. And it could easily be argued that four eight meter telescopes would be very nice, but that with three one could do already a great deal and then the cost reduction could be used to build an interferometric array of smaller telescopes. Of course, the three 8-m telescopes could easily become two and then one at even greater savings. I had always considered interferometry an interesting option for the VLT, but without much confidence in its early realization. True enough, one had already measured the diameters of some bright stars by interferometric methods; but until one would be able to make images and to reach faint objects, the scientific benefits seemed insufficient. The solution to the problem was to add two (now four) small mobile telescopes to the VLT. If more efficient ways to do interferometry with the large telescopes could be developed, then perhaps an integration of the whole setup would become worthwhile. Another reason to combine the VLT and the small telescope interferometry was that for a project of the financial size of the VLT it would pay to look for the world’s best site. Since interferometry was extremely sensitive to the “seeing” quality of a site, placing it at the best possible site was imperative. Thus, the proposal became to enlarge the VLT project of four 8-m telescopes by including some mobile 1.5-m (finally 1.8-m) auxiliary interferometric telescopes. This combination now looks optimal, indeed. A start has been made with a modest interferometric program, and the large telescopes have been successfully combined in some experiments. With the successful implementation of adaptive optics in the individual telescopes, the interferometric option now looks more promising. By the end of the Cargèse meeting a large part of the European community had become convinced that an array of something like 3–4 telescopes in the 8–10-m class was what was needed for the future. So in May 1983 a qualitative consensus on the scientific rationale and on the technological philosophy of the VLT was largely in place. Now it became necessary to convert these vague ideas into a project with a clear architecture and cost. While the Swings study group had done an admirable job in shaping an idea that enjoyed wide support in the community, this next phase clearly needed a much stronger engineering input. This could not be done on the basis of

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the part-time involvement of a few people. A full time VLT project group was needed which was soon set up, headed by Daniel Enard, with initially five full time persons, but also support from other parts of ESO. Since the VLT would become a major industrial project, this group needed a dedicated budget with which to award study contracts to industry to explore technical feasibility and cost. Furthermore, to continue the close connection with institutes in the ESO countries and to supplement the activities of the project group, a VLT Advisory Committee was set up with five working groups: Site Selection, High Resolution Spectroscopy, Low Resolution Spectroscopy, Infrared Aspects and Interferometry, in which 32 outside scientists participated, again under the overall chairmanship of Swings. Very early in the VLT studies it had appeared that while there would be many problems in mechanics and controls, the critical item, both technically and financially, would be the acquisition and polishing of the 8-m mirrors. The only European manufacturer of suitable mirror material was Schott in Mainz, which had developed “Zerodur”. This is a glass ceramic of excellent uniformity and polishability with a very low thermal expansion coefficient. So a mirror of Zerodur does not change its focal length when the temperature of the telescope changes. This is archieved by having on the microscopic scale a mixture of glass with a positive expansion coefficient and crystalline material with a negative one. At the appropriate temperature (⬃ 800 – 1000 °C) the glass slowly crystallizes; in the case of the 8-m mirrors the right balance would be obtained after about eight months. First, however, the glass disk has to have more or less the right shape. While for smaller mirrors, like the 3.5-m for the NTT, this may be achieved by machining away the necessary material, for large thin mirrors this would be very uneconomic. Hence, Schott proposed to use spin casting which they had previously used in other contexts. The molten material would be poured into a form having the shape of part of a sphere. When this form would be rotated, the centrifugal forces would give the upper surface also a concave shape. Upon cooling this shape would remain and thereafter the ceramization process would be started. So by the time the VLT proposal was written, the way to an 8-m blank was technologically clear. However, the existing facilities at Schott were inadequate and a new factory building would have to be constructed, which would add to the cost. Some informal discussions about a possible contract had taken place before the approval of the project, but neither the technical nor the financial viability had been unambiguously established. It was therefore necessary to study other possibilities in case unforeseen technological problems would arise and also to maintain a competitive pressure on the price. One alternative was to use fused silica. In fact, procedures had been developed by Corning in the USA for fusing silica pieces together, and this technology had no apparent size limits. A radically different possibility was to use metal mirrors5). These had been extensively used in the nineteenth century but abandoned because of

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the high thermal expansion and also problems with polishing and corrosion. An attempt at resurrecting aluminum mirrors had been made in the sixties, but had been unsatisfactory because of warping at the edges. However, this problem may have been more a consequence of the thin rimmed vase-like shape given to these mirrors than of the use of aluminum per se. Since the thermal expansion problem did not seem prohibitive if active optics were implemented, it seemed worthwhile to start a program of studies of metal mirrors. Actually the high thermal conductivity of metals might be an advantage in allowing a fast control of the temperature of the mirror to prevent turbulence in the air in the telescope tube above it. Aluminum had many attractive properties, but the drawback that it could not be polished. Thus, it had to be coated with a layer of harder material – actually canegen, a nickel alloy. The long term stability at the interface of the two materials was a source of concern. It therefore seemed attractive to look at harder metals that could be produced in large disks, and here steel offered itself as a low cost possibility. Among the specialty steels polishable materials could be found. Some steel disks were fabricated and initial tests were satisfactory (Figure IV, 1). Since the steel mirror tests involved only 50 cm disks, a substantial development program would still be needed for the metal option. The long term characteristics of the metal mirrors remained uncertain, while much experience existed with Zerodur. So it was decided to go for Zerodur in the VLT project plan, although for some time the metal option was kept alive, just in case.

Figure IV, 1. A 50-cm experimental steel mirror. At a time when it was uncertain that affordable Zerodur 8-m mirrors could be made, experiments were started at ESO with steel and aluminum mirrors.

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The metal development phase was concluded in 1990 with the successful fabrication and testing of two 1.8-m aluminum mirrors which were subjected to stringent thermal cycling, showing a good long term stability. By that time, however, a contract had been concluded with Schott which was completing the construction of a new facility for casting 8-m Zerodur disks. Since ESO had its hands full with the execution of the VLT project, it was not possible to invest further effort in more long term technological mirror developments. However, now that new, larger telescope projects are beginning to be discussed, it might well be worthwhile for technological institutes or universities to further study metal mirrors. Another important issue concerned the polishing of the mirrors for which a major new industrial facility would have to be constructed. This would include not only a computer controlled polishing machine, but also a tower of substantial height to house the necessary optics to test the mirrors. The tower was to be evacuated of the atmospheric air or perhaps to be filled with helium so as to avoid problems with variations in temperature with attendant optical refraction. This was particularly important because of the unusually tight tolerance imposed on the optics –80% of the light within a circle of 0.15 arcsecond diameter, almost a factor of three better than the specification of the 3.6-m telescope. While in the past the atmosphere had in practice limited image diameters to 0.5 arcsecond or more, speckle interferometry (the effective superposition of short exposures to reduce the effects of atmospheric turbulence) could do better, and the realization of the dream of compensation for atmospheric effects by adaptive optics was beginning to be clearly visible on the horizon. Two study contracts were given to Zeiss in Germany and to REOSC in France, the two companies in Europe with experience in the polishing of 4-m class mirrors. The results of these studies confirmed that the polishing of thin 8-m mirrors would be feasible and that the cost might be manageable within the VLT budget. Such thin mirrors are very delicate and have to be handled with care to avoid breakage. For example, lifting a thin mirror with only support at the edges would lead to a catastrophe. Another issue concerned transport, which would mainly occur over waterways. So the possibility for transport from the factory to the nearest waterway was studied. It was found that for an 8-m mirror there would be no problems, but for a 10-m serious difficulties would occur. After all it would not be very good to get stuck under a bridge! The issue of the mirrors is important for the technical aspects and the cost of the whole project. If the mirrors are heavy, the metal tube of the telescope has to become stronger and heavier and this weight increase propagates through the whole structure which has to be supported by more powerful bearings. Thus, the thinner the mirror the better. However, there are limits if the mirror is not to become too fragile and also because of the fabrication process. It is simplest to figure a mirror with a relatively long focal

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length. But if the focal length is long, the secondary has to be far away from the primary mirror, the telescope tube becomes long and heavy, etc. Also, the longer the telescope tube the larger the enclosure has to be, and this again augments the cost. The determination of the optimum characteristics of the mirrors to obtain the lowest cost is therefore a complex process. Finally a focal length 1.8 times the mirror diameter was chosen. Another issue was the housing of the telescopes. In the case of the 3.6-m telescope dome and building had accounted for nearly 40% of the total cost, which for the NTT had been brought down to 20%. The much reduced building cost would be accompanied by a significant improvement of telescope performance, since “dome seeing” associated with thermal disequilibrium of the air in the dome was much reduced. The question then was whether further improvements and cost reductions would be possible by operating the telescope in open air and having a simple housing to protect it during the day time or in bad weather. In this spirit a solution was explored where the four telescopes would be placed on a straight line, with during the night only a wind screen and during the day an inflatable dome as protection6). Such inflatable structures had been used in various places in the world to protect radar dishes. A 15-m diameter inflatable dome was ordered and placed at La Silla for experimental purposes. Of course, these inflatable domes were more complex than those for radar domes, since they should be opened every night. A model of the VLT (Figure IV, 2) with the inflatables was made and extensively used for familiarizing the scientific community and governmental representatives with the VLT. Since this created the image de marque of the VLT, it seemed dangerous to change it before the project was approved. However, in the “VLT Proposal” it was made clear that this was “only the presently nominal solution within a general concept”. Perhaps not surprisingly wind tunnel experiments later showed that cylindrical structures with a natural but controlled air flow were superior to the open air operation, especially when the wind was relatively strong. Also the linear telescope array seemed non optimal for interferometry, and the four telescopes were finally placed in independent enclosures in a somewhat different configuration. The mirror disks, the polishing and the enclosures together were estimated to account for half of the telescope cost. At the same time they created most of the uncertainty. There were, of course, many other issues of importance to be considered. The mechanical structure (Figure IV, 3) had to be optimized to avoid vibrations, the design of the active optics system and the mirror cells had to be refined and scaled up from the NTT design and the control system had to be upgraded with newer computers. In the early developments the software aspects took second place, but in order to obtain a working telescope a major software effort would be needed. All of this was essential for the functioning of the VLT, but one had enough knowledge to see how this could be done and to determine the cost with some confidence.

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Figure IV, 2. The first VLT model. The four 8-m telescopes were placed on a common platform in inflatable shelters. Observations would be made in open air, and to reduce the effects of wind, a screen would be mounted on the side of the prevailing wind. At the bottom of the telescopes the pipes are visible that would bring the light beams from the unit telescopes to the interferometric laboratory in the middle to the left. The linear arrangement was not optimal for interferometry, and there was concern about turbulence created by the wind screen. So later the telescopes were placed individually in protective enclosures.

A difficult issue arose with the secondary mirror. Since in the infrared beyond two microns there is strong background radiation due to the atmosphere and the telescope, it is essential to continuously monitor the background when measuring the flux from a weak source. The optimal way to do this is to wobble the secondary – to move it back and forth between two positions as frequently as possible – and then to measure the difference signal between the source position and the background reference position. But in an 8-m telescope the secondary mirror is a large (1.2 m), massive object and to move this back and forth some ten times a second is no small matter. It is therefore important to reduce the weight of the secondary as much as possible.

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Figure IV, 3. Early model of an 8-m unit telescope. The support structure for the elevation axis is placed on the large circular azimuth bearing. The two yellow boxes contain instruments with the light entering through the elevation axis. The light beam to the coudé focus and to the interferometric laboratory passes through the white tube. The Nasmyth mirror which directs the light into the elevation axis is just visible At the time no Cassegrain focus was foreseen, because it would necessitate an increase in the height of the elevation axis and a mechanism to remove the Nasmyth mirror out of the Cassegrain beam with significant cost implications. In later designs of the telescope tube (Figure V, 4) fewer tubular structures of greater strength and a solid center piece replaced the numerous small elements to improve the stiffness of the tube.

While a tolerable result could be achieved with a zerodur mirror, a substantial weight reduction would very much enhance the performance. The possibility of beryllium as a mirror material was therefore explored. This material is not easy to handle being quite poisonous as a powder. Some experience had been gained in space applications, though only with smaller mirrors. Ultimately beryllium mirrors were chosen, but serious problems were encountered before full success was attained. Of course, the wobbling secondary also had to be made compatible with the active/adaptive optics system.

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One issue led to controversy: should the unit telescopes have only the two Nasmyth foci that naturally go with the alt-azimuth mounting or should there also be a Cassegrain focus? Not surprisingly the scientists wanted this, since it reduced the number of reflections from three to two with a 15% reduction in light losses. In addition, it would have a much improved polarization performance. However, the technical implications were serious. For the light to reach the Cassegrain focus the Nasmyth mirror would have to be removable out of the light path. Moreover, to have space for the Cassegrain instruments, the altitude axis would have to be moved higher with consequences for the mechanical structure and the enclosure. It was clear that all of this would have a significant cost impact, and so it seemed dangerous to include it in the baseline VLT proposal; however, the Cassegrain option could be reviewed later. A year thereafter, when a new Director General had taken over, that review led to the inclusion of the Cassegrain. It was approved by Council without much discussion of the increased costs that would be incurred. Not surprisingly it was later claimed that the VLT proposal had underestimated the costs. A realistic analysis ten years later showed that the extra costs incurred were largely the consequence of such extra requirements (see chapter V.). The VLT project group, which between 1983 and 1987 gradually increased from 5 to 10 persons, made a very complete preliminary design, outlining also choices that could be made following more detailed studies. The resulting proposal, including the cost estimates, inspired confidence. Particular care was taken to remain consistent: The 16-m equivalent diameter never varied, the four telescope array concept was there from the beginning, though the exploration of alternatives was necessary to establish that this was really the optimal solution. And most importantly for gaining support from the governments in the member countries, the overall financial envelope remained the same during the ten years leading up to the proposal in 1987. Galileo had made the first telescopic observations of stars and planets in Venice. So it was only appropriate that ESO presented the VLT design to the European astronomical community in Venice at the end of September 1986 at a workshop at the beautiful property of the Cini Foundation on the Isola di San Giorgio (photograph overleaf). Some 80 scientists participated, and a consensus of the great majority was achieved. In March 1987 the complete proposal (dubbed the “Blue Book”) was presented to Council. Much of the rest of the year was used for the resolution of the last political problems. In some countries these centered around the issue of what national projects should be reduced or abandoned. Finally, in December 1987 Council unanimously approved the project with a total budget of 388.2 MDM (1986), corresponding to 300 M€ (2004), including instrumentation and interferometry. Only six member countries could guarantee their participation. However, in 1988 also Belgium was able to join, followed by Denmark in 1989. The largest project ever undertaken in ground based astronomy was on its way.

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V. Construction of the VLT

Could we handle that dumb thing or would it handle us? I felt how confoundedly big, was that thing … Joseph Conrad1)

While many aspects of the realization of the mechanics, electronics and enclosure would require much effort at ESO and in industry, there were no unsurmountable problems in view. The mechanics had been well studied and even though no fully optimized design existed yet, the design one had made met the minimum specifications for flexure and resonant frequencies. Computers and electronics in general were in a state of flux with every year important industrial advances being made. ESO had constructed the NTT and even without further technological improvements it could, if need be, be adapted to meet the requirements of the 8-m telescopes. Experiments had been made with the inflatable shelters and the results were encouraging, even though not everyone thought this was the way to go. But the design of the NTT enclosure could easily be scaled up. The situation was much less clear with regard to the optics. No one had cast an 8-m mirror blank and no one had polished one. This had been the reason to explore other possibilities during the design phase. However, since 3.6-m Zerodur blanks had been cast in Europe with a good record of thermal stability and polishability, there was an obvious preference for this material. Thus, soon after approval of the project discussions were started with Schott about a contract for the delivery of four 8-m mirror blanks. Since the existing factory at Mainz was inadequate, a new building would have to be constructed, which obviously would add to the cost. The negotiations with Schott were difficult. An initial informal Schott offer was not accepted by its board of directors. As a result, an offer from Corning in the US was 22% cheaper with a schedule at least a year shorter. Since ESO preferred the Zerodur option because of the excellent uniformity

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of the material and because it came from European industry, further negotiations followed which finally led to a price reduction of about 20% though increased with future inflation corrections2). After many more discussions about the details, the contract at 47.5 MDM + cost variation (~ 35 M€, 2004) was signed in September 1988. However, permits for the construction of the new factory had to be obtained and the new factory had to be built. The firing of the new furnace took place in October 1990. The first three blanks cracked3), which was not unexpected, since no such large pieces of Zerodur had ever been made, and so a learning process was needed. As a result, significant delays were incurred and the first blank was delivered in June 1993 (Figure V, 1), about 2 1/2 years later than foreseen in the Blue Book. This delay continued throughout the whole project, though the fourth blank had been delivered on schedule at the end of 1995, and the polishing also went faster than anticipated. In the meantime discussions took place with the two firms in Europe that would be able to develop the tools for polishing 8-m mirrors. This led in July 1989 to the award of a contract for 33.75 MDM (~ 25 M€, 2004) to REOSC near Paris for polishing the four 8-m mirrors4). Again, this involved construction of a new building with a high test tower and the development of a new computer-controlled polishing machine. With the two critical

Figure V, 1. The disk of Zerodur for the first 8-m mirror at Schott. The yellow color of the rather transparent material is noticeable. The disk was still to be ceramized for eight months at temperatures of 800 – 1000 °C.

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contracts for the mirrors concluded, at a price below that foreseen in the Blue Book, it was clear that the VLT as an industrial project was on its way. In mid-1993, the first 8-m blank arrived at REOSC after a week long travel through European waterways. The grinding and polishing operation could begin. In 1995 the last blank was ready at Schott, and the polishing of the first one was completed at REOSC. Four years later four outstanding mirrors had been completed (Figure V, 2), and the first two were mounted in their telescopes to produce some stunning images which demonstrated their high quality. The investment at REOSC paid off well. Subsequently, it won the contract for polishing the two eight meter mirrors for the Gemini Project, a U.S. led consortium, including the UK. Though the mirrors were the most critical part of the VLT, the amount of work that needed to be done at ESO was quantitatively relatively limited. Once the optical specifications had been made, ESO had to check that they had been met, but no further design work was needed. It was very different for the overall structural design in which ESO had a more direct involvement; it had to ensure that the many other mechanical parts would be integrated in a coherent way. In 1990 ESO tendered for the main mechanical structure of the four telescopes. Several offers were received, the lowest one from an Italian consortium Ansaldo/EIE/SOIMI. This appeared to be an entirely suitable offer. Even though ESO does not follow a juste retour scheme to distribute industrial orders proportional to the national contributions, it seemed a very lucky circumstance that the three big countries each had obtained a large

Figure V, 2. The 8-m mirror being polished at REOSC. On the right a polishing tool is seen attached to the computer-controlled machine.

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contract in the VLT. Moreover, ESO had had a positive experience with Ansaldo during the construction of the NTT. However, one of the unsuccessful companies complained and the Finance Committee did not approve the contract; instead the suggestion was made to hold a meeting of all the bidders, ESO management and Finance Committee to discuss “technical and juridical points of the contract”5). This certainly was an unusual notion, which reflected national greediness on the part of some delegates. As a result, a 5 months’ delay was incurred and much time wasted by ESO staff before construction of the mechanics could start. The contract was finally concluded in September 1991 for 79 MDM (~ 54 M€, 2004) Two other mechanical items were particularly critical. The mirror cells with all the electro-mechanical active supports for the thin 8-m mirrors were determinant for the optical quality of the telescopes. The cells should give a sufficiently rigid support to the 150 axial supports (pushing in the direction parallel to the telescope tube) and 64 radial supports, but at the same time be as light as possible since a weight increase would propagate through the whole telescope structure (Figure V, 3). In addition, attached to the cell would be the Cassegrain instrumentation as well as the support structure for the (removable) Nasmyth tertiary mirror. Two parallel design studies were contracted out for nearly 8 MDM each to two different firms, and one of these, GIAT in France, thereafter fabricated these units for about 40 MDM (~ 25 M€, 2004). In fact, the total cost of these units significantly exceeded the cost of the polishing of the 8-m mirrors. An interesting aspect of the active optics system is that the changeover from the Nasmyth to the Cassegrain focus may be made without a change of the secondary mirror as in conventional telescopes. By modifying the curvature

Figure V, 3. The mirror cell. The thin 8.2-m mirror is supported axially by 150 motor controlled pistons which are part of the active optics system.

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of the primary mirror which is possible because of its thinness, one may switch between the two foci. Equally difficult and costly was the secondary mirror unit. Made of beryllium, the polishing was a delicate operation (REOSC) while the mechanics (Dornier) were complex since the 1.2 m mirror should wobble at frequencies over 10 cycles per second and also be part of the active optics setup. While these two items led to a significant cost overrun (Table V, 2) over the Blue Book, they have much contributed to the excellent performance of the telescopes (Figure V, 4). Thermal control of the telescopes and their environment was of prime importance. If the primary mirror is warmer than the air in the telescope tube, convection will arise which deteriorates the image quality. On the other hand, on humid days a cold mirror could suffer from condensation. So a back plate on the mirrors had to control their temperature precisely. Also turbulence in the enclosures could pose a serious problem. The design of the appropriate air conditioning system therefore was critical. In the Blue Book design the telescopes were enclosed in inflatable shelters which appeared to provide a particularly low cost solution. Night time operation would be in the open with the wind blowing away the turbulent air. Experiments were made with a 15-m inflatable dome placed at La Silla and wind tunnel tests were conducted. Fear of problems with wind forces on the 8-m mirrors led to the decision to place the telescopes in more conventional, but well ventilated, rotating metallic enclosures. A formidable task remained. A large number of smaller and larger motors and sensors was needed to control the movable parts, more than 200 for the active optics systems in each telescope alone. Electronic hardware was needed to connect these to the control computers. Software had to be developed to ensure that everything would function coherently and automatically. This represented an enormous effort under the leadership of Manfred Ziebell. In the past much of the software for telescope control and operation had been developed at ESO. However, with many standardized, reliable commercial and industrial packages now available, it was preferable to use these as the basic software building blocks. In the beginning the NTT software had been considered as a prototype for the VLT. In the end the opposite happened and the improved VLT software was retrofitted onto the NTT. In addition, the instruments at the twelve foci had to be integrated with the telescopes and their output had to be displayed and archived conveniently. At the end of 1990 Paranal had been chosen as the site for the VLT (chapter VI.)6). It then became necessary to determine the layout. Some 28 m of rock were blasted away from the top of Paranal to create a large enough platform (Figure V, 5). This had to be done cautiously in order not to fracture the rock on which the telescopes would be placed. In the Blue Book design the four 8-m telescopes were located on a straight line. However, the linear array was not optimal for interferometry. It was replaced by a

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Figure V, 4. One of the four finished 8-m telescopes. Note the much simpler structure with fewer, but stronger elements than in the first design (Figure IV, 3). Just below the center piece the location of the Nasmyth mirror is visible which directs the light beam through the elevation axis. When it is removed the light can pass through the hole in the primary mirror to the Cassegrain focus below. Around the primary mirror the edge of the mirror cell is visible with the wiring that connects the actuators supporting the mirror. At the top is the secondary mirror made of beryllium. It can oscillate between two positions at a high frequency during observations at infrared wavelengths.

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Figure V, 5. The four telescopes at Paranal in the early evening. Some of the shutters in the enclosures have been opened to let the cool air freely circulate. The octagons in front are supports for the movable 1.8-m auxiliary interferometric telescopes. The building to the right is the upper part of the interferometric laboratory, where the light from the different telescopes may be combined. Just to its left the first 1.8-m auxiliary telescope is visible and behind it the housing of the 2.5-m VLT Survey Telescope.

crescent-shaped arrangement which is more advantageous for interferometry. A maze of tunnels would connect the four telescopes and the 1.8-m mobile auxiliary ones to the central interferometric laboratory. At a distance from the telescope area other elements of the infrastructure would be located: workshops, a residential building, an electricity generating plant and a water reservoir. The latter would be replenished by water regularly trucked in from Antofagasta, since no local water wells were to be found in the dry desert. The most critical item was the mirror washing and aluminizing plant made by AMOS (B) and Linde (D). The vulnerable 8-m mirrors were transported to this plant and placed in the vacuum chamber in a series of highly automated operations. The old Panamericana (unasphalted) connected the Paranal area with Antofagasta, but the local roads in the Paranal area had to be made. Construction of the infrastructure started in 1991 and continued into 2002 when the temporary huts for lodging the staff were replaced by the elegant Residencia, complete with swimming pool and even several palm trees (Figure V, 6a). Most areas of the Residencia are climate controlled, since the extreme desert air is too dry for long term

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comfort. The building is largely underground with a 35-m semitransparent dome ensuring a luminous aspect. Of course, during the night precautions are taken to ensure that no light escapes to the outside. The 175 m long façade, with behind it the rooms for the staff and with small windows to avoid the strong glare, blends perfectly into the surrounding desert (Figure V, 6b).

Figure V, 6a. The Residencia. In the central area a garden gives some greenery to the staff in an otherwise extreme desert environment. The completely air-conditioned building is mostly located underground, but natural light may enter through the 35-m dome. Provisions have been made to ensure that at night no unwanted light pollution is produced.

Figure V, 6b. The façade of the Residencia, behind which are the rooms for the staff and visitors.

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The design of the building was the result of an international competition won by the architects Auer & Weber (Stuttgart). Most of the basic design was done by the architect D. Schenkirz, while the interior aspect of the building owes much to Daniel Hofstadt, ESO’s representative in Chile. The 11 M€ Residencia has contributed significantly to make life of the staff liveable in the harsh desert. From this brief description of the various activities relating to the realization of the VLT, it might seem that most things went rather smoothly. However, along the way some obstacles were encountered which led to delays which, as always, also had cost consequences. Two of these stand out. Less than a year after the approval of the VLT project Council became concerned about ESO’s management and expenditures. As Pierre Léna said in Council7), the French astronomers had had to agree to close some national facilities to obtain VLT approval. A parallel effort on the part of ESO would be desirable, with a stronger focus on the VLT. Of course, in some of the other member countries the situation was no different. As the concern of Council increased, Council set up a VLT management review board which reported in May 1990. Among other items the board was concerned about significant morale problems among the staff and recommended the appointment of a VLT program manager8). ESO involved a costly high powered management consulting firm, which identified 131 potential candidates9). Finally someone was appointed, who left nine months later after having introduced much additional bureaucracy. A few years thereafter, for the position of Head of Administration, the experience was repeated with another consulting firm10) with an equally distastrous result. Whatever their merits in other circumstances, business consultants apparently do not have much of a feeling for the requirements of an international, scientific/technological organization. Immediately after the departure of the new project manager, Massimo Tarenghi, who had already brought the NTT project to a successful conclusion, was appointed as his successor11). The situation in the ESO Council remained difficult, with several times the three large countries outvoted by the five small ones. While it is true that according to the ESO Convention each country has an equal vote, it is also evident that an organization cannot be run against the will of its principal paymasters. So a change was needed, and Council appointed Riccardo Giacconi as the new Director General as of January 1993. A period of American style management followed. While this did not please everyone, it created the conditions under which the VLT project could be brought to a fully successful conclusion. Council received a clear view of the problems and their solutions. But the management problems had set the project back by the better part of a year. In the meantime, a serious issue had arisen in the relations between Chile and ESO which were governed by the “Acuerdo” concluded in 1963. In the beginning everything went very smoothly, and relations between ESO and

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the Chilean government, as well as with the small astronomical community and with ESO’s local staff, were excellent. In 1972/73 economic conditions in Chile became difficult and a black market appeared which created opportunities for some and difficulties for others. Then at the end of 1973 came the Pinochet coup. Relations between European countries and Chile became very cool, with ESO being in the middle. Obviously, it was important for ESO to continue to have positive relations with the government in power, and equally obviously some governmental delegates in the ESO Council could not agree to this too openly. In a confidential session of Council I said: “If you live in hell, you treat with the devil”, and this argument led to a tacit understanding allowing us to continue our relations with the government at the required level. Relations with the community and local personnel were not helped by ostentatious consumption by some European staff. Since cars could be imported tax free and sold on the Chilean market two years later, a curious traffic arose with even medium level personnel owning or driving top of the line Mercedeses or Maseratis. Evidently, this created resentments, which were not diminished when the Pinochet government donated the land around Paranal for a gigantic European project. With the election of a democratic government in December 1989, some of these resentments came to the fore. The Chilean astronomers claimed observing time at ESO, the staff wanted improved conditions, and the original owners, the inheritors of the La Torre family, claimed the land of Paranal. Though worthless desert, multi million dollar claims were made. A Chilean astronomer consultant for the claimants made complex calculations partly based on the documents I had presented to Council in which the astronomical excellence of the site had been described. He arrived at a sum of some 30 MUS$! The issue of guaranteed observing time for Chilean scientists had been raised already early in 1988 by the foreign ministry in Santiago12). Although this was repeated several times thereafter, it had not been taken sufficiently seriously by ESO13). During 1994 negotiations took place between the Chilean government and ESO, and in November of that year an agreement was initialed. Unfortunately, this provisional agreement had not yet settled the ownership of the land. A century earlier it had been a reward for heroic deeds during the war with Bolivia and Peru. This gave the issue an even stronger patriotic flavor. The Chilean parliament also entered into the fray, and soon a local judge violated ESO’s diplomatic immunity and ordered a halt to the work at Paranal. Fortunately the Chilean foreign minister J.M. Insulza gave strong support to ESO and a final agreement was signed in April 1995. Towards the end of the year the Chilean government settled matters with the La Torre relatives for a substantial sum. It is undoubtedly the first time in history that such a sum has been paid for a piece of real estate exclusively on the basis of its value for astronomy. In September 1996 the Chilean senate followed congress in ratifying the “Interpretative, Supplementary and Complementary

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Agreement” to the 1963 Acuerdo. This gave Chilean astronomers rights of up to 10% of the observing time at ESO telescopes and also contained provisions aligning the statute of the Chilean workers closer to the Chilean labor law. It is not evident that the latter was to their advantage, but it satisfied a strong sentiment. While this new acuerdo appears to have solved all problems, the activities on Paranal had been set back by about half a year. Subsequently, the relations between Chile and ESO rapidly improved and now are very positive and cordial. So on 4 December 1996 the “Foundation Ceremony” for the Paranal observatory could take place in the presence of the President of Chile, Eduardo Frei Ruiz-Tagle, and many other dignitaries. Relations with the Chilean astronomical community also became much more positive. When ESO came to Chile there were few astronomers, mainly at the Cerro Calan observatory of the Universidad de Chile in Santiago. Programs included a radio survey at 7 m wavelength which has yielded an excellent map of the southern sky. Some photometry was done and also astrometry, the latter subsequently in part with an astrolabe in cooperation with ESO. Some four decades later astronomical activity in Chile is expanding rapidly, with greatly invigorated departments at the Universidad de Chile and at the Universidad Católica, also in Santiago. Moreover, new programs in astronomy were started at universities in Concepción, La Serena and Antofagasta14). Of course, the instrumental opportunities at ESO and at the US sponsored observatories played a role in this, as did increased governmental funding, augmented by some support from ESO. The move of ESO astronomers back to Santiago facilitated interaction between the two communities, fostering joint research projects, colloquia, etc. The general improvement of the universities and technological institutes also created a steady stream of competent engineers and technicians which allowed ESO to recruit locally an increasing fraction of its staff. In fact, at Paranal and La Silla well above 75% of the technical staff is now Chilean. The events at Paranal had a precursor at La Silla. There ESO had bought the land from the government for 45,000 Escudos (8,000 US$). Some time thereafter a person appeared who claimed ownership of part of the land. Since a court case would have held up the start of activities at La Silla for a long time, ESO paid another 15,000 Escudos to deal with this claim15). Unfortunately, the sum at issue at Paranal was so much larger that the same approach was not possible. Subsequently, activities at Paranal proceeded at a rapid pace. By the end of 1996, parts of the structure of the first unit telescope arrived, followed a year later by the first 8-m mirror. On 25 May 1998 “first light” was achieved at the completed telescope, followed at 10 months intervals by Unit Telescopes 2 and 3. Finally, UT 4 saw first light on 3 September 2000, thereby completing the VLT as such. It had taken 23 years since I had first proposed that ESO construct a 16-m equivalent telescope and nearly 13 years following

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project approval. Of course, much work remained to be done before every last adjustment would have been made. However, it is a tribute to the quality of ESO’s staff and of their industrial partners that soon thereafter the VLT was fully functional according to its specifications without significant mishaps appearing along the way. The four 8-m telescopes are only part of the VLT project. Each telescope has to be equipped with instrumentation – imagers and spectrographs for different wavelength regions. Already in the Blue Book it was clear that ESO could construct in-house only a small part of the instrumentation; most of it should be contributed by institutes in the ESO countries. This had the further merit of making the VLT project a community wide effort: ESO would provide much of the necessary funding for the acquisition of hardware and industrial contracts, while the institutes would design and develop the instrumentation and would obtain in exchange a certain number of observing nights. From the experience with the 3.6-m telescope, it was clear that work on the instruments should begin as soon as possible. So in 1990 the first instrumentation plan was developed and two years later the first contracts were concluded with institutes in the member countries. Instrumentation is discussed in chapter VII. The other aspect of the VLT is interferometry. In the Blue Book provisions had been made for adding two mobile auxiliary telescopes of about 1.5 m in diameter to improve the interferometric image quality obtainable with the four stationary telescopes. Subsequently, the MPG in Germany and l’INSU (CNRS) in France suggested that they could provide a third auxiliary telescope in exchange for observing time13). However, ESO’s financial problems led to the elimination of the interferometry from the near term financial plan. Some years later, interferometry was successfully brought back into the planning16) and a contract was concluded with the MPG and l’INSU17). Subsequently Belgium offered to pay for most of a fourth telescope and with support from some other countries it could be acquired. The increase of the diameter to 1.8 m and of the number of small telescopes from two to four are of great benefit to the whole program. A further increase to six would be very much worthwhile. The layout and various subsystems were completed or on their way when in 1998 the contract for two, later increased to four mobile 1.8-m telescopes was signed with AMOS in Liège at about 5 M€ per telescope. The last of the four should be completed in 2006. Work on instrumentation for the VLTI also progresses at various institutes (see chapter VII). In the meantime successful interferometric observations have been made with the large telescopes.

Planning and Reality In December 1987 the Council approved the VLT project as presented in the “Blue Book” with a budget of 382.2 MDM (1986 value), corresponding

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to 272 M€ in 1999 according to ESO’s inflation calculation, which is based on some kind of weighted average of inflation in the relevant European countries, where ESO makes its purchases. In 1999, when about 90% of the total had been spent or contracted, it was found that the actual cost amounted to 313 M€, 15% in excess of the 272 M€ in the Blue Book. In Table V, 1 a comparison is given in more detail (where we have omitted the 20 M€ for the interferometry which has become very much open ended), from which it appears that the extra costs came from three items: the cells supporting the 8.2-m mirrors and the Nasmyth mirror units, the secondary mirror units and the costs of Paranal developments. An important part of these cost increases is due to additions made to the project after its approval. The most evident of these are the Cassegrain foci for all four telescopes. Access to the Cassegrain focus requires removal of the Nasmyth unit out of the light beam. Not only did this very much complicate the mirror cell and the M3 unit, it also caused cost increases in the telescope structure; the height of the altitude axis had to be increased to make space for the Cassegrain instruments. So overall weight increased. Furthermore it required additional focal plane instrumentation (adapters/image rotators/etc.) at the Cassegrain focus. It is difficult to reliably determine the extra cost incurred, but I would estimate it to be in the 15–25 M€ range. Of course, there is no doubt that from a scientific point of view the implementation of the Cassegrain foci has been very much worthwhile. Table V, 1. Comparison of the VLT budget approved in 1987 (Blue Book), updated to 1999 values, with actual spending (90%) through 1999 + foreseen thereafter (10%). All values have been converted to M€ . The contingency (20 M€) in the Blue Book has been distributed over the various items. Major additions to the scope of the project are indicated by + or ++. These include the four Cassegrain foci and the four beryllium secondaries. Interferometry is not included in the table, since its scope had not yet been decided.

Item 8.2-m mirrors M1 cells + M3 units M2 units Main telescope structures Other telescope items Infrastructure / buildings / enclosures Instruments TOTAL

Blue book 65 15++ 7++ 43 31+ 58 33+ 252

Actual

Difference

57 32 26 43 28 80 27

–8 + 17 + 19 0 –3 + 22 –6

293

+ 41

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The question of the wobbling secondary for IR observations was left rather open in the Blue Book, with some doubt expressed about its necessity. As a result, a rather modest sum was foreseen for this item, though mention was made of a sophisticated system based on beryllium mirrors, which had been used in some space applications. Later it was decided to implement such mirrors at all four telescopes, which led to a quadrupling of this budget item. Finally, also the cost of Paranal development increased substantially. In part this was related to additions made beyond the perhaps somewhat too primitive setup initially foreseen. Since life in the Atacama desert has its difficulties, the more comfortable surroundings created for the scientific technical staff are certainly beneficial. In conclusion, it appears that the estimates made in the Blue Book were essentially correct. The cost overrun of 15% is largely the result of increased demands made on the VLT following its approval. The same conclusion was reached already during the program audit in 1994. The audit committee wrote then18): “We cannot argue that the increases are only due to the increased scope of the project, errors in the initial estimates may also play a significant rôle, but the correspondence between the most significant cost increases and the areas of project modifications is striking.” Of course, the contingency included in the original budget was there to deal with possible errors in the initial estimates and not for covering an enlargement of the project. In the Blue Book also the schedule of the project was specified. The first 8.2-m blank was to be fabricated in three years, by the end of 1990, and to be polished three years after that. However, as explained before, the first blank was completed 30 months late. Other delays resulted from the management problems in Europe, from the contract difficulties for the mechanical structure and from the political problems in Chile. The first unit telescope suffered most and had a delay of about four years, the last one of only 2 1/4 years. But what counts is that at the end of the construction process, Europe had completed the world’s most powerful telescope as planned and placed it on the world’s clearest site.

Other 8-m class telescopes Not surprisingly, other countries have also decided to construct large telescopes. By the end of 2006 the total number should be fifteen, including the four of the VLT (Table V, 2). In addition there are two large telescopes of more limited steerability and optical quality for spectroscopic purposes. The two 10-m Keck telescopes, built with private and NASA money, may also be used interferometrically, but, of course, only one baseline (85 m) between the large telescopes is available. This somewhat restricts the potential, because “phase closure” techniques cannot be used, since these require at least three

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telescopes. However, it is planned to add also some smaller auxiliary interferometric telescopes. By 2004 the necessary permits had still not been obtained because of eco-religious claims on Hawaii. The 10.4 m Spanish Gran Telescopio de las Canarias (GRANTECAN, Figure V, 7) with a segmented mirror is essentially a copy of the Keck telescopes. Funding came in part from the EU which has programs to support

Table V, 2. The world’s 8-m class telescopes.

Diameter

Name

Country

Year

4 × 8.2

VLT

ESO

1998/00

2 × 9.8

Keck

US

1993/96

2 × 8.4

LBT

2004/05

10.4

GRANTECAN

US, D, I 1/2 1/4 1/4 ESP, …

2006

8.2

Subaru

Japan

1999

8.0

Gemini N

8.0

Gemini S

US (1/2), 2000 UK (1/4), Can … US (1/2), … 2002

6.5

Magellan I

US

2002

6.5

Magellan II

US

2003

6.5

MMT +

US

2002

9.2

with limitations HET US …

2000

9.2

SALT

2005

SA,

Location Paranal Chile Mauna Kea Hawaii Mt. Graham Arizona La Palma Canaries Mauna Kea Hawaii Mauna Kea Hawai Pachon Chile Las Campanas Chile Las Campanas Chile Mt. Hopkins Arizona McDonald Texas Sutherland S. Africa

Alt (m)

Type

2700

Z

4200

S, Z

3200

BSC

2400

S, Z

4200

ULE

4200

ULE

2700

ULE

2400

BSC

2400

BSC

2600

BSC

2100 1800

S: Segmented; Z: Zerodur (Schott); BSC: Borosilicate Ceramic (U. of Arizona); ULE: UltraLow Expansion (Corning).

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Fig. V, 7. Model of the 10-m GRANTECAN on La Palma.

activities in less developed regions in Europe. Placed at La Palma, it may also help to determine the suitability of that site for even larger future telescopes. The two 8-m Gemini telescopes – one in the northern and the other in the southern hemisphere – represent a cooperation between the US (~ 50%) and the UK, Canada, Australia, Argentina, Brazil and Chile. Funding is governmental. The solid 8-m mirrors have been polished by REOSC. Optimization for the IR has been stressed. The most innovative of these new telescopes is the Arizona (1 / 4)/Germany (1/4) / Italy (1/4) / other US (1/4) Large Binocular Telescope, originally called the Columbus Telescope, which was later considered “politically incorrect” in the US. It has two 8-m telescopes in a common mounting. This has the advantage that interferometry between the two is possible over a relatively large field, but, of course, there is not much choice in baselines. The LBT has suffered major delays because of native Indian and ecological claims about the site at Mt. Graham in Arizona. While the red squirrels were still being hunted in various places, it was said that the telescope construction would risk the extinction of the subspecies on the mountain. Actually, their numbers appear to have increased after construction began! The first mirror was installed in 2004, the second should follow a year later. Perhaps the most innovative feature is the thinness (1.6 mm) of the 91-cm secondary mirrors.

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Supported by (or rather hanging on) 672 actuators, they allow the adaptive optics to be implemented without auxiliary optics and so to avoid the corresponding light losses. Rather contradictory statements about the cost of the LBT have been made with values around 140 MUS$ (excluding instrumentation) being plausible. The more limited HET and SALT have composite mirrors made of numerous spherical segments. Moreover, these telescopes can only track in azimuth which limits observing time on any object to less than an hour. However, they have a large collecting area (70 m2) at low cost (25–30 MUS$). They should be particularly suitable for spectroscopy of objects of intermediate brightness. With GRANTECAN, LBT and Gemini N, the European countries have the equivalent of 2 1/4 telescopes of the 8–10 m class in the northern hemisphere to supplement the four of the VLT in the south.

VI. Sites for Telescopes

The only remedy is a most serene and quiet air such as may perhaps be found on the tops of the highest mountains, above the grosser clouds. Isaac Newton1)

The earth’s atmosphere has negative effects on astronomical observation. Clouds, haze and dust absorb the light from celestial sources. Turbulence in the atmosphere causes small temperature variations which lead to small scale variations in the atmospheric refraction (the bending of light) which smear out images of astronomical objects. Thus, a stellar image which should be essentially point-like is smeared out over a “seeing” disk of typically an arcsecond or less in diameter on good sites and more than that in poorer places. Some of the turbulence is caused by layers of varying wind speed rather high in the atmosphere (some km), some occurs close to the ground by the effect of the surface features on the wind driven air and some results from convection when the lower air is too warm for a stable atmospheric structure. With the advent of infrared astronomy the total atmospheric water vapor content has become important since water vapor absorbs incoming radiation and itself emits infrared radiation which gives the IR sky a luminous glow which makes it difficult to detect celestial sources. Submm radio waves are also subject to much absorption from water vapor. Newton already suggested that it would be advantageous to place a telescope on a high mountain, where one would have left some of the ill effects of the atmosphere below. However, according to Piazzi Smyth2) Newton’s “very simple and probable piece of speculation” had “dropped out of notice” and when he was going to put it to the test “a few voices even loudly proclaimed that high mountain tops, all the world over, are invariably loaded with clouds and mist and sleet and tormented forever with impetuous storms”. This led him in 1856 to mount an expedition to Teneriffe where he found that stars four magnitudes fainter could be observed from a site 2700 m high on

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the Teíde volcano than at sea level (Figure VI, 1). It is interesting that the expedition was made possible by Mr R. Stephenson, a member of the British parliament, who provided his own yacht, because “his early experiences on South American cordilleras had long since led him to look with favour on Newton’s mountain method of improving astronomical observations”. More than a century later his experiences were amply confirmed. In the tropics humidity is high and atmospheric convection strong. At latitudes around 50˚ the jet stream generates strong turbulence, while cloudiness is relatively high. As a result, most high quality astronomical sites are found at subtropical latitudes. A notable exception is the high central Antarctic plateau. It is high, very cold, extremely dry and in contrast to the Antarctic periphery without strong winds. However, it is no simple matter to build and operate a telescope there, though some specialized instruments have been erected. Over land temperatures are rather variable and this creates instability. Above the oceans the air flow tends to be much more stable, in particular when cold currents cool the oceanic surface. Then a temperature inversion (temperature increasing upwards) occurs which inhibits convection. At the boundary of this layer, typically a km high, low clouds are common, but higher up the atmosphere is calm. Thus, high island or coastal sites bathed in cold water have long been believed to be particularly favorable for astronomical observation. However, at sufficient altitude the coastal advantage seems to be less strong.

Figure VI, 1. The Teíde Observatory (2390 m) on Tenerife. In the background is the Pico de Teíde (3700 m) which last erupted in 1798. The volcano is still slightly active today and the observatory has been built on its shoulder. To the right is the 90 cm French-Italian solar telescope THEMIS, and to the left the German 40, 45 and 60 cm solar towers, the Spanish 1.5-m infrared telescope and an ESA-Spanish optical ground station (1-m) for tracking space debris and space communication experiments.

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Because of the rotation of the earth, cold currents coming down from upwelling circumpolar waters tend to occur on the east side of the oceans. Of course, geographic constraints also play a role. In the northern hemisphere cold currents along the coasts of California and West Africa have created favorable conditions, in particular on the Canary Islands in front of the African coast. Here the island of La Palma with its 2400 m high volcanic rim is an excellent site (Figure VI, 2). The Pico de Teíde on Tenerife at 3700 m is unsuitable because of volcanic activity, but seeing conditions on its lower flanks are excellent, in particular for solar observations. Thanks to Francisco Sánchez, major observatories have been developed on both islands. Conditions in

Figure VI, 2. The Roque de Los Muchachos Observatory (2400 m) on La Palma some 140 km NW of Teíde. A large number of telescopes has been placed close to the upwind rim of an extinct caldera. These include the 2.5-m Nordic Optical Telescope, here just visible on the rim, the 1-m, 2.5-m and 4.2-m telescopes of the UK-NL cooperation, a Liverpool University 2-m, a Flemish 1.2-m and the 3.5-m Italian “Telescopio Nazionale Galileo”, as well as 96-cm Swedish and 45-cm Dutch solar telescopes. The 10-m Spanish “Gran Telescopio de las Canarias” is currently nearing completion. The La Palma Cosmic-Ray Observatory observes the Cerenkov light produced by cosmic gamma-rays of very high energy with MAGIC, seen here in front, a 17-m diameter segmented telescope. Since no high optical resolution is required, a place in the wind shadow was acceptable.

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southern Spain, where the German Calar Alto observatory, with its 3.5-m telescope, was placed, are less favorable3). The best place in the northern hemisphere is probably Mauna Kea at 4200 m on the big island of Hawaii. Because of its high altitude and stable oceanic environment, water vapor column density is low and seeing conditions are as excellent as at La Palma. Several US telescopes, including the two 10-m “Keck telescopes” are placed here. Also the UK (now joined by the Dutch) placed here the 3.6-m infrared telescope UKIRT, while France participates (now at 45%) in the 3.6-m Canada-France-Hawaii telescope. In addition, the 15-m submm JCMT radio telescope is operated by the UK in collaboration with the Netherlands. As several of the best places on Mauna Kea and La Palma have been taken, other northern hemisphere sites have been looked for. At sufficient altitude the difference between oceanic and continental sites may well become smaller. In fact, Germany and Italy – each at 25 % – participate with the US in the Large Binocular Telescope (2 × 8 m), the first half of which became operational in 2004 on Mt. Graham in Arizona at 3200 m. Also optimistic speculations are being made about high sites in central Asia, but only limited reliable data are available to date. Turning now to the southern hemisphere, we find cold currents along the western rims of three continents. In Western Australia there are no high mountains. In South Africa ESO found relatively modest conditions, but further north at the Gamsberg in Namibia – a table mountain 2350 m high – conditions have been claimed to be comparable to those at La Silla. Because of political problems, German attempts to place telescopes there have come to naught. An earlier expedition by the Smithsonian Institution to Fogo (2700 m) in the Cabo Verde islands and to six peaks in Namibia concluded that the sites were all unsuitable for measuring the solar radiation intensity, which requires a very pure sky with high IR transparency and therefore a low column density of water vapor4). By far the strongest cold current – the Humboldt current – flows along the South American coast and brings cool conditions even to the equator. When Humboldt reached the Peruvian coast in 1802, he measured a temperature of 16 °C – more than 10° lower than normal so close to the equator5). Close to the coast, frequently at no more than 100 – 200 km, the Andes rise to above 6000 m and form a barrier against humidity coming from the Atlantic. The result is an extremely dry coastal strip, with the Atacama desert being one of the driest areas on earth. As a consequence, some of the world’s finest sites for optical and for submm telescopes are found in Chile.

Early Astronomical Sites in Chile The early history of Chilean astronomy has been well described by Keenan, Pinto and Alvarez6). The first organized astronomical activity in

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Chile was the Gilliss expedition of the US Navy (1849–52) for observations of stellar and planetary positions. Subsequently, his observatory in Santiago was taken over by the Chilean state with the founding of the National Observatory. In 1893 a solar eclipse was observed near the town of Vallenar (50 km north of La Silla), where several expeditions had gone to profit from the clear skies. In 1903 Lick Observatory placed a 92-cm telescope on San Cristobal, close to Santiago, where during 26 years the radial velocities of southern stars were measured with the Mill’s spectrograph. From here H.D. Curtis in 1909 made an expedition to the region NE of Copiapo and reported the night sky to be “very transparent and clear”, estimating that some 300 nights per year might be cloud-free7). From 1920 to the early fifties C.G. Abbot from the Smithsonian Institution conducted a program at Cerro Montezuma to measure the intensity of the solar radiation (the “solar constant”)4). According to Abbot, this site at -22.5 ˚ latitude near Calama was the best place he had found in the southern hemisphere for his observations which required high IR transparency. It is interesting that the excellent sites found by ESO are all close to the one Abbot found without all the modern data and equipment available now. In the late fifties F. Rutlland, the director of the Chilean National Observatory, induced G.P. Kuiper – one of the great astronomical entrepreneurs – to consider the possibility of an observatory in Chile. In 1959 J. Stock arrived to make detailed site surveys first in the vicinity of Santiago, but rapidly moved north where clear skies appeared to be more frequent. Stock8) extensively studied Cerro La Peineta near Copiapo and Cerro Tololo further south, which was subsequently chosen by the Americans for their observatory. From Stock’s results it appeared that the Chilean sites were substantially better than those in South Africa, where ESO had been studying several places9). In December 1962 A.B. Muller then visited La Peineta and Tololo for a total of 27 nights, and in 1964 ESO selected Cerro La Silla (Figure II, 3) 100 km north from Tololo situated between La Serena and Vallenar (Figure VI, 3). The ESO Council had made the choice contingent on water being available near the site, and subterranean water was found in 1965 in one of the old river beds below La Silla. The choice of La Silla had also more political aspects. There had been a growing concern in ESO circles about developments in South Africa, and the discovery of the superiority of the Chilean sites therefore came as a relief10). There then were discussions about joining the Americans on or near Tololo11). While in particular the more American oriented Dutch were very favorably inclined to such an association, others were more concerned about the independence and visibility of the European entity. In retrospect, the decision to go to an independent mountain was certainly the right one. Different ways of doing things would have led to problems, and ESO with its limited experience would have been very much the junior partner. Relations between the observatories always remained very cordial.

Figure VI, 3. Map of northern Chile. Squares indicate cities; circles indicate observatory sites, filled circles those currectly active with telescopes of 2-m or more.

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O. Heckmann, who became ESO’s first Director General, found easy access in Chile due to the strong element of German descent in that country. With K. Walters, an international lawyer who had handled many delicate matters during the war and who had a very extensive set of friends and acquaintances, Heckmann negotiated a treaty between Chile and ESO as an intergovernmental organization, which gave ESO many immunities and considerably facilitated future operations. Without waiting for Council approval, he signed the treaty, an act of independence which, though not applauded by everyone at the time, much speeded up ESO’s installation in that country11). At the same time, ESO’s quasi-diplomatic status complicated relations with Tololo and an independent site became even more necessary. While without further site surveys it was clear that the various mountains between La Serena and Copiapo should have excellent conditions, it remains remarkable that no local survey at all was conducted before the selection of La Silla. In retrospect, this may have been all to the good in accelerating the construction of the observatory. While ESO could be satisfied to have escaped the deteriorating political situation in South Africa, its optimism about Chilean politics was less justified. In this seemingly so peaceful country several violent revolutions and coups d’état had taken place since independence, and the next one was to come in 1973 12). In these troubled times the “acuerdo” negotiated by Heckmann proved to be of great value. Also the astronomers from the USSR were attracted by the Chilean skies, and in 1967 a small astrometric observatory was built on Cerro Roble, some 80 km north of Santiago6). Site surveying for a larger observatory came to an abrupt halt after the 1973 coup. Finally, in 1970 the Carnegie Institution of Washington built its observatory at Las Campanas, 50 km north of La Silla. By the late seventies large telescopes had been installed at Tololo, La Silla and Las Campanas. The high quality of the three sites was confirmed and many scientific results were obtained. However, these sites were not as excellent in the IR as Hawaii at 4200 m altitude because of a higher atmospheric water vapor content. In the meantime, the Astronomy Department of the Chilean University had begun in 1966 to take a new look at the north. J. Stock who by then was based at the National Observatory gives a brief description of the conditions there13): “There are a number of mountains of sufficient elevation south of the town of Antofagasta and very close to the coast. The abrupt rise from the Pacific Ocean on one side, and a large flat plain, more than 1000 m lower, on the other side give these mountains rather special conditions. High stability, that is, good seeing, is expected for night time conditions. Furthermore, the extremely low humidity makes this area very suitable for astronomical work in the infra-red. Since this area is absolutely arid, water supply for an observatory will be difficult and costly. Underground currents may exist, but most likely at a prohibitive distance and depth.” Since water sources had been a major concern in the location of the various observatories, Stock thought that sites further to the East, where

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abundant water falls on the high Andes, would be preferable. Accordingly, he selected a site for further study at 20 km from San Pedro de Atacama, the flattish summit of Cerro Chaupiloma at 3300 m altitude. According to Stock a nearby river had sufficient flow for a hydroelectric power plant! Somewhat later, in 1971, astronomers from the USSR started measurements also on this mountain as well as on Cerro La Peineta14). Moreover, in 1967, the National Observatory reported that sites for a radio telescope had been looked for at the Salar de Atacama and that a suitable 6 × 3 km area had been found at 20 km from San Pedro15). After the coup in 1973, the Chilean activities of the Academy of Sciences of the USSR came to a sudden end, the Americans and Europeans were busy with the construction of their observatories, and for the Chileans other concerns predominated. Interest in the North largely vanished.

The New Push Northward During 1977 I initiated plans for a future large telescope at ESO. Technical studies were made, and it became clear that the Very Large Telescope would be expensive – well above a hundred million euros. It also seemed probable that the VLT would be constructed as an array of several large telescopes and that there was no suitable place at La Silla for such an array. These two factors together implied that a new site had to be looked for, and that site quality might be more important than low cost, at least as long as that cost was small compared to that of the telescope array. Within the ESO territory two mountains seemed to offer possibilities of comparable quality: Cerro Duran to the north halfway to Las Campanas, and Cerro Vizcachas closer to La Silla to the southeast. A visit to Cerro Duran showed a suitably shaped free standing summit. However, the layout of a road to La Silla was far from evident. In any case, the time needed to drive from one site to the other would be too long to have a common infrastructure. Cerro Vizcachas was easier to reach and a provisional road was constructed for testing. The top had enough space to accommodate the VLT. While there was some concern that this site was relatively close to the southern border of ESO’s territory and, therefore, of the area protected from mining, overall it seemed the most attractive in the La Silla area. So this became the reference site for comparison with others. To the east of La Silla much higher mountains could be found. One of these, Cerro Peralta, was clearly visible on the sky line as a free standing 4500 m high summit. An expedition there by D. Hofstadt and myself showed access to be very difficult. Much running water was found on the lower slopes, the result of frequent summer rains which appeared to be related to thunderstorms drifting in from Argentina. Towering clouds can frequently be seen over these high mountains which only rarely reach La Silla. While it may well be that winter nights with extremely low water vapor content can be found there, the overall level of cloudiness would be higher than at La Silla.

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It therefore seemed that if more exceptional sites were to be found we would have to go northward (Figure VI, 3, 4). From La Silla to the north cloudiness slowly diminishes as may be seen from Stock’s data near Copiapo who found there 20% more clear night hours than at Tololo. Partly because of stronger winds the site had not been selected by the Americans. Much further to the north at the cosmic ray station at Chacaltaya (5400 m, near La Paz, Bolivia) measurements had been made which showed much more cloudiness and for its altitude a relatively high atmospheric water vapor content16). In between there should be an optimum.

Figure VI, 4. Satellite image of northern Chile taken by the ESA astronaut Claude Nicollier on his way to the Hubble Space Telescope. North is towards the lower left. The curving coast line north of Arica and the anvil like figure at Antofagasta are easily recognized. Along the coast clouds above the Humboldt current stabilize the atmosphere, but remain well below the level of Paranal. Further to the east of Antofagasta one can see the eastward curve in the main chain of the Andes with the whitish Salar de Atacama, an ancient dried up lake with below the surface brines which contain much of the world’s exploitable lithium. Somewhat further to the NW the plume of the copper smelter at Chuquicamata, near Calama, is visible. To the east of the Salar de Atacama, in between the first mountains, is the Llano de Chajnantor – site for ALMA, the Atacama Large Millimeter Array. On this image the blocking of humidity from the Atlantic and the general increase of the cloudiness towards the more tropical areas of Bolivia is also in evidence.

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A visit was made to La Peineta, the 3000 m high mountain near Copiapo, by A. Ardeberg and myself; we found the road to the top very damaged (by rainfall), and since Stock had already investigated the site at some length some years earlier, it did not seem worth the effort to set up a site testing station there. All of the sites which had been studied till then were relatively far inland. But for astronomical sites the more stable oceanic air has a great advantage. So when one evening I looked again at a large map of Chile, it struck me that there was, in fact, a rather unique high mountain very close to the coast, Cerro Paranal at 2700 m. Later I realized that it was located in the general area south of Antofagasta that Stock had referred to. So why not have a look? Soon thereafter, in March 1983, I mounted an expedition (Figure VI, 5) during which the extreme dryness, the purity of the sky, the general suitability of Cerro Paranal (Figures VI, 6, 7) and the relatively easy access along the old Panamericana were seen from land and from the air17). By September Arne Ardeberg had set up a meteorological station where every two hours the general condition of the sky and also the integrated atmospheric water vapor content were measured in addition to the standard meteorological quantities. The local dryness was so extreme that at times it was thought that the hygrometer had gotten stuck at zero! This station, under the direction of Marc Sarazin, has remained in operation for more than two decades with increasingly sophisticated instrumentation - including also a seeing monitor, the Differential Image Motion Monitor which he built. It was temporarily dismantled when the top of the mountain was removed for the VLT construction. Following the establishment of the monitoring station at Paranal, Ardeberg made repeated visits to some other mountains in northern Chile, transporting in particular a second apparatus for measuring total atmospheric water vapor. Carrying such a 25 kg instrument on foot from 5500 to 6000 m at the top of Cerro Tacora was no mean feat! The conclusion of Ardeberg’s work was that only at substantially greater altitude could lower atmospheric water vapor be found and that the high sites east of San Pedro sometimes suffered from cirrus clouds, which would be unfavorable for optical observations18). Once seeing measurements were started at Paranal by Sarazin, the exceptional qualities of the site were confirmed. Not only was the frequency of clouds half of that at La Silla, but seeing was significantly better with the light of a point source smeared out over an area on average 25% smaller. Furthermore, during the nine driest months water vapor content was substantially less that at La Silla. So after six years of cloudiness measurements and two years of seeing measurements, in 1990 Paranal was chosen as the site for the VLT19). In retrospect the issue of the availability of water, so important in earlier site selections, seems curious. If no local water is available, it can be

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Figure VI, 5. The first expedition to the Paranal area. From left to right: Gerhard Bachmann, Hans-Emil Schuster, the author and André Muller, photographed by Ulla Demierre. In the background is the escarpment which terminates the higher area around Paranal. Figure VI, 6. Image of the Paranal area taken from SPACELAB with the University of Munich camera. The summits of these mountains are exceedingly dry which is very important for observations in the infrared. Because of large climatic fluctuations from year to year, it was necessary to continue the ESO studies of atmospheric conditions in this region for seven years, before a definite decision about the VLT site was made. Conditions were monitored in particular at Cerro Paranal (2700 m) close to the Pacific coast and occasionally at Cerro Armazoni (3000 m), the isolated mountain half way up along the right side of the picture. The old Panamericana highway passes just east of the north–south escarpment in the middle. The scale is 6 km/cm. North is up.

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Figure VI, 7. The Paranal area photographed by C. Madsen and H. Zodet. In front of the Pacific, Co. Paranal connected by a road to the NTT hill and to Co. La Montura on the right. The VISTA optical/infrared wide field telescope will be placed on the NTT hill, so named because I considered placing the NTT there rather than at La Silla.

brought in by truck at a cost that is manageable. The same is done at several Chilean copper mines. And it is interesting to note that for the city of Antofagasta with 300,000 inhabitants much of the water is transported from the east by a pipeline, since none is available locally. Even during the darkest political periods, nobody has seriously disrupted that water supply. In the meantime a desalination plant has also been built. Today all the water for Paranal is bought near Antofagasta and trucked to the mountain.

Millimeter Sites The very high sites in the main chain of the Andes had been inspected rather casually during the VLT site surveys. Numerous high mountains, with altitudes up to 6000 m, were found in the latitudes considered. Low water vapor column density was found, substantially lower than at Paranal, but the relatively high frequency of cirrus clouds made the area less attractive for optical telescopes and so no measurements of seeing had been made. Since such cirrus is composed of small ice crystals it does not affect mm radio waves which are absorbed only by water vapor. Also large areas were excluded by the smoke from the Chuquicamata copper smelters, which could be traced visually for more than 100 km to the east. In between the mountain peaks high plateaus are found, and these have drawn the attention of radio astronomers looking for a site for a large submm interferometer for which large flat areas with very low water vapor column density are required. The Nobeyama Radio Observatory (Japan) has been

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testing an area (Río Frío at 4200 m) 180 km SE of Antofagasta in the Cordillera Domeyko, while the Europeans visited the nearby Pampa San Eulogio, a flat area 20 × 20 km at 3700 m altitude. The US National Radio Astronomical Observatory has extensively studied a higher site at 5200 m, the Llano de Chajnantor, 300 km east– north–east of Antofagasta, 60 km from the picturesque village of San Pedro de Atacama and conveniently just a few km from the road to Argentina (Figure VI, 8). This site appears to be exceptionally dry and has been selected as the location for ALMA, the Atacama Large Millimeter Array – which will combine the American, European and Japanese projects (see Chapter IX)20). It remains to be seen how many scientists and engineers are able to work at this altitude. In my (qualitative) experience most people are able to cope with the conditions at 4000 m but at 5000 m this is much more difficult to do. However, with an operational facility at 2900 m where most engineering activities will take place, the situation should be manageable. The 12-m radio telescopes can be transported there for refurbishment.

Figure VI, 8. The 5000 m high Llano de Chajnantor. Scattered over an area 10 km in diameter, the 64+ submm telescopes of 12-m diameter of the Europe-Japan-US ALMA project should be in place here by the end of 2011.

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Climatic Variability Some observatories have been placed in the wrong spot on the basis of site testing of inadequate length. Almost every site has substantial yearto-year variations, and a short campaign will tend to lead to the selection of a place that had an above average quality during that time, even though on a long term basis it could be inferior. To avoid such problems, the site testing for Paranal continued for more than six years before a decision was made. Since then the conditions at Paranal have been monitored for a period three times longer (Figure VI, 9). According to Sarazin21), for the 20 year interval 1984–2003 photometric nights (with clear sky for at least six consecutive hours) averaged 76%, slightly below the 80% of the first six years, but remained well above conditions at observatory sites elsewhere. The La Silla average was 61%, essentially the same as the the 62% found there during 1966–75. In both places there seems to be some tendency for above or below average conditions to persist for several years in succession. Seeing conditions also have varied. At Paranal the 0.7 arcsecond mean seeing of the years 1987–1997 quite suddenly deteriorated to values around 0.9 arcsec for 1998–2003. The more fragmentary La Silla data also show a deterioration at about the same time. At both sites 2002 was the cloudiest year ever. Note that the seeing values are mean values. Median values are typically 10 better. Also these data come from the seeing monitor which appears to overestimate the image diameter measured by the VLT telescopes by some 10% in the visible and up to 30% at 2.4 μm21). The climate in the eastern Pacific appears to be subject to cyclical variations on various time scales. The variable El Niño – La Niña cycles of typically half a decade are, of course, well known to be associated with climate events over a good part of the earth. Recently a 50 year cycle has been found22). During the cooler half of the cycle in the eastern Pacific anchovies were abundant, to be replaced by sardines during the warmer part. The transition between the two appears to be rather abrupt. The fish catches have enabled two such cycles to be identified during the twentieth century. The last warm phase began in the mid-seventies and ended in the mid to late nineties. Rather remarkably, at La Silla and Tololo the annual number of photometric nights diminished significantly around 1976, only to recover some twenty years later – with the exception of the catastrophic year 2002. Large fluctuations possibly associated with the higher frequency El Niño– La Niña cycles superposed on the longer term trends are not unexpected. Changes on even longer time scales have also occurred. Anecdotal evidence was provided by locals at Pelícano near La Silla who stated that half a century earlier tall grass was growing where now not much vegetation is to be found. The Pelícano river, ESO’s source of water, went underground and only reappeared for a few months during the nineties. Also the derelict

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Figure VI, 9. Evolution of annual mean conditions at Paranal (■) and at La Silla (■). The upper graph gives the fraction of photometric nights, the lower graph the mean diameter of the seeing image in arcseconds. Incomplete data are indicated by open symbols. The horizontal bar in the upper graph represents the average for the La Silla data for 1966–1975. For 1993 and 1999 the incomplete La Silla seeing data have been combined with those for the preceding year to obtain 12 months of data appropriately distributed through the year. The figure is based on monthly data provided by M. Sarazin21).

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irrigation ditches in the La Silla area suggest a wetter past climate. More quantitatively at La Serena the rainfall appears to have diminished over the past century by 63%23). It is perhaps not surprising that the La Serena – La Silla area would be particularly sensitive to climate changes. Over the 300 km distance between Copiapo and La Serena average annual rainfall during the 1971–1984 period varied from 11 to 78 mm24), to increase a further factor of 4.5 over the 400 km to Santiago. With such strong gradients relatively small changes in the location of the pressure systems can have very large local effects. In that respect Paranal is better situated within a wide latitude range with rainfall below 10 mm per year. Latitude shifts of a few hundred km of pressure systems would be expected to cause less change at Paranal. Of course, rainfall and astronomical conditions are not quite the same. In particular, seeing may depend on more subtle effects. In fact, Sarazin has noted that the deterioration of the seeing at Paranal over the last years appears to be related to a change in the large scale pressure distribution which shifted the winds more to the NE. On much longer time scales, some recent studies seem to show that the climate in the region east and north of the Salar de Atacama was very dry much of the time25). The very dry period during the late parts of the last ice age was followed by a somewhat more humid interval from perhaps 16,000–10,000 years ago. Numerous archeological remains are found around ancient lake shores which date to this period. An extremely dry period thereafter left the area uninhabited. A certain recovery to slightly less dry conditions took place subsequently, but the record from different sites is sometimes contradictory. The last 4000 years appear to have been more or less as at present. In one of the lakes on the altiplano the water level never exceeded present values during the last 9000 years. Thus, the astronomical sites in northern Chile may look forward to a continuation of present day favorable conditions unless unforeseen effects of global warming intervene.

Sites for future telescopes The quantitative comparison of sites involves a number of parameters. Clear sky is obviously essential. “Photometric nights” are commonly defined as nights with at least six consecutive hours of clear sky. When also shorter periods are included, the time is referred to as “spectroscopic” or “usable”. The additional time may be used for obtaining spectroscopic data like redshifts where only the wavelength of spectral features is needed. However, to obtain accurate photometrically calibrated spectral data, sufficiently long continuous periods of observation are needed. The second essential parameter is the “seeing” or more specifically the diameter of the image of a point source due to atmospheric turbulence. The turbulence may be excited, for example by instabilities, at the interface of

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atmospheric layers moving at different speeds. The simplest way to measure the seeing is to take images with large telescopes. Since these are not transportable, other methods are needed to compare sites. Moreover, when the housing of a large telescope contains air at different temperatures, the local “dome seeing” may make site conditions seem worse than they are. At ESO Marc Sarazin has built the DIMM, the Differential Image Motion Monitor26). It consists of a 35-cm telescope with in front of a detector a mask with two small holes separated by perhaps 20 cm. The two resulting images are continuously moving over the detector because of the atmospheric turbulence. The relative motion of the two images gives quantitative information about the turbulence. On the assumption that the distribution of the turbulent elements follows a standard (Kolmogorov) law, the turbulence is fully characterized and the image that would be observed with a large telescope may be inferred. The great advantage of the DIMM is that contrary to earlier instruments it only measures relative motions of the images and so it is impervious to movements of the telescope by the wind or other causes. At Paranal the actual images observed with the VLT are some 10% smaller in the visible and, therefore, better than inferred from the DIMM. This is presumably related to the fact that the larger turbulent elements do not follow the standard distribution. The DIMM or some version thereof has now become a worldwide standard for seeing measurements. When adaptive optics systems (Chapter VII) are considered for correcting the turbulent effects on the images, other site parameters become of interest: the number of turbulent layers, their altitude and the speed at which they move. These may be determined by campaigns with balloon borne equipment, lidars, echo sounders, etc. Unfortunately, such campaigns tend to be of short duration. A third main parameter is the quantity of water vapor above the site. IR observations are affected both by the emission from the H2O in the atmosphere and by its absorption of the radiation coming from the outside. The quantity of H2O in vapor form is measured in mm of precipitable water. Ice crystals in cirrus clouds are largely irrelevant in the IR, though they are a hindrance to observations in the visible. H2O may be measured from its IR emission and from its absorption of radio waves at submm wavelengths. A site with 1 mm of H2O is excellent, but several mm are found at typical observatories. Not surprisingly, the best results are obtained at high, cold sites. Data for a selection of sites are assembled in Table VI, 1. Seeing measurements have been transformed to median values on the ESO DIMM scale. The table documents the remarkable frequency of clear nights at Paranal, which appears to be unparalelled in the world. For its altitude it is also particularly dry. Chajnantor is, of course, much drier, but the available information suggests that clouds are more frequent. Cornell University has started a site testing campaign on Co. Chico, about a hundred meters above the Llano de Chajnantor27). Seeing measurements yielded a median value of 0”71 compared

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to 0”80 at Paranal during the same 38 nights. However, the distance of some 300 km between the two is probably too large for reliable conclusions to be based on so few nights. The Cornell study indicated that a few hundred meters higher above the plateau the dryness may become even more extreme, but obviously life becomes more difficult. The Argentinian side of the Andes does not appear to offer advantages compared to Chile, and the same appears to be the case for southern Africa and Australia. Sarazin performed some limited testing for ESO on the island of La Réunion, but conditions were not particularly favorable19). Turning to the northern hemisphere, I would doubt that any US sites would be suitable for new large European telescopes. Some continental sites are good, but not as outstanding as Mauna Kea on the big island of Hawaii. There the fraction of clear sky is perhaps on the modest side, but seeing and low H2O are excellent. According to the Keck telescope website image diameters have a median value of 0”55. When comparing Paranal and Mauna Kea, we should take into account that the median values are some 10% smaller than the mean values given in Figure VI, 9. Moreover, the DIMM results are some 10% larger than the directly measured image diameters. Taking also into account the fraction of photometric time, the number of hours with sub 0”6 seeing should be comparable on the two sites. However, Mauna Kea begins to be rather full, and the religio-ecological problems, which have caused long delays both there and at Mt. Graham, make these sites not very attractive for a large European telescope. In that respect the Mexican sites, like S. Pedro Martír or Sierra Negra, are more promising27). High sites in central Asia could perhaps have been worth considering28), but political factors effectively exclude large investments there. Maidanak in Uzbekistan appears to have excellent seeing (0”69 median, comparable to Paranal intercalibrated with ESO instruments), but the 60% clear sky is disappointing. Hanle in the Indian Himalaya also appears to be rather good. The low water vapor values at St. Katherine in the Sinai4), combined with the recent easy accessibility of the Red Sea resorts, makes this perhaps an interesting area for further study for a regional telescope. For Europe the most suitable site for a large northern hemisphere telescope would appear to be La Palma. The median seeing of 0”65 on the better subsites (intercalibrated with ESO) is excellent29); unfortunately, the 3.7 mm median column density of H2O is not30). The percentage of photometric nights is acceptable, but on the low side31). The mean seeing of 0”75 compares well with the long term average at Paranal of 0”80, though for the number of photometric hours with excellent seeing the latter still has the edge. The La Palma site is situated in Spain and, therefore, in the EU, while the national and regional governments have demonstrated an admirable engagement for its protection. Perhaps with JWST and ALMA expected to be in operation early in the next decade, the H2O problem should carry less weight than the excellent seeing. In any case, on the basis of presently available

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Table VI, 1. Astronomical sites. Subsequent columns give the altitude in m, the percentage of photometric nights, the percentage of “spectroscopic” or usable time, the median seeing in arcsec as measured by a DIMM, the median column density of H2O in mm and the longitude and latitude. Note that these data sometimes are based on insufficiently long observations to yield a reliable long term average. Figures placed between the ph and sp columns give the percentage of clear time without the requirement of 6 hours continuously clear. Alt. Chacaltaya Chajnantor Paranal La Silla El Leoncito Mauna Kea S. Pedro Martír Sierra Negra Kitt Peak Mt. Graham McDonald Obs. La Palma Oukaimeden Calar Alto Maidanak Hanle La Réunion AAO Dome C

(Bolivia) (Chile) (Chile) (Chile) (Argentina) (Hawaii) (Mexico) (Mexico) (Arizona) (Arizona) (Texas) (Spain) (Marocco) (Spain) (Uzbekistan) (India) (France) (Australia) (Antarctica)

5400 5200 2700 2400 2400 4200 2800 4600 2100 3200 2000 2400 2700 2200 2600 4500 2900 1100 3250

% ph

% sp

)1

DIMM

)1

( (63) 76 61 48 55 64

( (81) 91 82 72 81

64 38 51 30 53 (38) 40 >755

67 75 65 73 652 57 60 71 (69) 65

H 2O 2.32

.703 .843 .604 .60 .73

1.2 2.2 3.8 2.0

6.72 2.9 .65 .92 .69 .8

.275

3.7

<2 (5) 0.255

I

b

68W 68W 70W 71W 69W 155W 115W 97W 112W 110W 104W 18W 8W 3W 67E 79E 55E 149E 123E

–16 –23 –25 –29 –32 +20 +31 +19 +32 +33 +34 +29 +31 +37 +39 +33 –21 –31 –75

average day time cloud cover 53%. 2 day time. 3 mean value × 0.9. 4 image diameter × 1.1. 5 winter only.

1

evidence, there would be only three plausible sites for a large European telescope: The Paranal area (Armazoni?), one of the summits around the Llano de Chajnantor and La Palma. Moving the NTT from La Silla to the Chajnantor area might be an effective way to test its suitability for future large telescopes. For the other two sites telescopes of sufficient size will continue to provide data for a comparison. Concerning Paranal and surroundings, much will depend on whether the deterioration of the last six years is a temporary aberration or not and on whether it affects Armazoni equally. Finally, it might be worthwhile to further study the Mexican sites which look promising, but for which the data are still very limited. Another site that at present evokes much interest is the South Pole. In the interior of Antarctica winds are very weak and the atmosphere extremely dry and cold. The SP is not very suitable for most observations in

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the visible, because it is astronomically dark (Sun more than 18 ° below the horizon) for only 79 days per year. Moreover, a turbulent layer at low altitude causes the seeing to be terrible. However, in the IR and submm domain this is not so much of a problem. Measurements made at 350 μm show that in the zenith direction the median atmospheric transmission is 0.30 versus 0.25 at Chajnantor and 0.15 at Mauna Kea28). The stability of the transmission is particularly favorable at the SP. However, the fraction of the sky accessible at small zenith angles is small, while at low latitude sites like Chajnantor it is much larger. For special projects, like the high precision determination of the fine structure of the Cosmic Microwave Background, the SP appears to be unsurpassed, but for a broader range of programs the advantage over sites like Chajnantor is not evident. Moreover, the Cornell measurements have shown that the water vapor content of the atmosphere above the Llano de Chajnantor may diminish rapidly with height27). So conditions on the surrounding mountains may well be as good as at the SP. Conditions appear to be much more favorable at “Dome C”, a high Antarctic plateau (3250 m) some 15 ° from the SP. Here a French-Italian cooperation has constructed the “Concordia” base for a variety of purposes. Dark time and the area of the sky at low zenith angles are already more favorable. The most outstanding characteristic of Dome C is its incredibly stable atmosphere. Recent measurements of atmospheric turbulence correspond to wintertime seeing with a median of 0.27 arcsec, spectacularly better than anywhere else in the world32). Also the angular distance over which the turbulent patterns are correlated and the slowness of their variation appear to be optimal. Though a longer term data set would be desirable, it seems probable that both for observations in the IR and for interferometry in the visible Dome C would offer unique advantages. However, in the absence of a large base at Dome C, it would not be very realistic to try to place a 100 m telescope like OWL there. So far we have discussed only conditions in the atmosphere. A serious threat comes from city lights, which even at tens of kilometers distance may cause a significant increase in the background luminosity of the sky. Even at La Silla and still more at Tololo this is becoming noticeable. Fortunately, the authorities in La Serena and in the Atacamean region are beginning to impose standards on street lighting which reduce the upward flux33). This has both economic and astronomical benefits. The difficult conditions of life in the Atacama desert for the moment limit light pollution at Paranal, though mining operations pose an ever present threat. In fact, the Yumba mine SE of Paranal has become increasingly visible. The commercial exploitation of space may also pose grave dangers. Various proposals for space advertising have been successfully defeated for now. However, experiments have been made to light cities in the Arctic by solar reflectors, and the risks to ground based astronomy are all too real.

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In Chile earthquakes pose an additional danger. While modest earthquakes cause no greater problem than the temporary loss of the telescope pointing, larger ones may do more lasting damage. From the data of Barrientos34), an earthquake stronger than 7.5 on the Richter scale may be expected in the Paranal region once every 250 years. Of course, the damage would depend very much on its precise location. So the risk is small, but real.

VII. The VLT Observatory: Adaptive Optics, Instruments, Interferometry and Survey Telescopes

Die Daten der kosmischen Schöpfung sind ein nichts als betäubendes Bombardement unserer Intelligenz mit Zahlen, ausgestattet mit einem Kometenschweif von zwei Dutzend Nullen, die so tun, als ob sie mit Maß und Verstand noch irgend etwas zu tun hätten. Thomas Mann1)

The VLT array of four 8.2-m telescopes has been built, but many other aspects have to be taken care of before it could be a fully functioning observatory. The deleterious effects of the atmosphere have to be mitigated to obtain the full benefit of the large unit telescopes. A wide variety of instruments is needed to analyze the light collected. A substantial infrastructure is required to make use of the VLT as an interferometric array. And, finally, since the large telescopes can observe only a minuscule fraction of the sky, it would be beneficial to have wide angle survey telescopes – the successors to the Schmidt telescopes of the past – to discover important objects for the 8.2-m telescopes to study in detail.

Adaptive Optics (AO) The performance of ground based telescopes is degraded by the earth’s atmosphere, while space based telescopes are very expensive. So simple economics tells us that we should look for ways to reduce the atmospheric effects. In the ultraviolet the ozone layer is opaque, and in part of the infrared various atmospheric constituents block the incoming radiation. So in these wavelength ranges we have no choice but to observe with space telescopes.

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There are also some wavelength ranges in the IR where water vapor is the main problem. Hence, the selection of high, dry sites is advantageous. Observations at some submm wavelengths may be made from places like Chajnantor, Mauna Kea or even better from the high, cold Antarctic plateau. But even in the optical/near IR spectral domain from 0.3 – 2.5 μm, where the transparency is good, there is a serious problem: the atmospheric turbulence disturbs the incoming light rays making the astronomical images unsharp, or in astronomical parlance causing “seeing”. Typically the seeing smears out the image of a point-like star over an arcsecond or more, far larger than the intrinsic diffraction image of a telescope a few meters in diameter. This was one of the reasons the 2.4-m Hubble Space Telescope (HST) was constructed, which gave spectacular images with much fine detail not seen on images from ground based telescopes. However, by now, new technologies are being developed – adaptive optics – which allow equally excellent images to be obtained from the ground, at least in the near IR. When different layers of the atmosphere move at different speeds, turbulence tends to result at the interface. Different parcels of gas – different cells – then move in randomly different directions and at different speeds. This also causes small temperature variations, as a result of which the light rays passing through the medium are refracted and this leads to the diffusion of the images. The smallest turbulent cells are only a few cm across, and the pattern of cells may change on millisecond timescales. Suppose now that we take the image of a star with only a millisecond exposure time. Then the turbulence will effectively be “frozen”. The image of the star will be deformed by the turbulent medium, but during the millisecond it will not change much. We then observe another star, so near to the first one that its light passes through the same turbulent pattern. Its image will be deformed in the same way. We analyze the image of the first star, and we can find out how it has been deformed from the point-like image it should have had in the absence of the atmosphere and what corrections have to be applied to the deformed image to recover the true one. We now can apply these same corrections to the neighboring star and also recover its image. The next millisecond we will find somewhat different corrections, and again we can restore the image of the second star with these, and so on. Of course, all of this only works if the first star is sufficiently bright so that there is enough information in the image to determine the corrections. But the second star can be very much fainter or it may be a more composite image, like a double star that due to the seeing could not be resolved. In principle, to make an adaptive optics system we could deform the primary mirror of the telescope in such a way that it corrects for the seeing effects in exactly the same way as the active optics system in Figure III, 4. Instead of making the mirror optically more perfect as in that case, we could introduce the imperfections needed to compensate the seeing

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effects. However, the primary mirror is generally too heavy to do this on millisecond timescales. So a thin flexible mirror is introduced into the optical beam with the necessary actuators to shape it. Alternatively, it may be feasible to achieve the same result directly with the Cassegrain secondary mirror if it is made sufficiently thin2). The principle of adaptive optics is identical to that of active optics. However, apart from the faster response that is needed, there is one fundamental difference. The active optics corrections are valid in the whole focal plane. But since the turbulence pattern is different in different directions, the adaptive optics corrections are only valid in close proximity to the star from which they are determined. The size of the “isoplanatic patch” over which the corrections are well correlated depends on the wavelength. In the optical at 0.5 μm it is typically 2 arcsec on a good site. But in the near IR at 2.5 μm it would be about 14 arcsec. Also the corrections change more slowly. The number of actuators needed on the deformable mirror is proportional to the square of the diameter of the primary mirror. For an 8.2-m VLT telescope it is about 6000 at 0.5 μm wavelength, but at 2.5 μm only 125. So adaptive optics is much simpler in the near IR than at visible wavelengths. At ESO the first adaptive optics instrument was developed very much under the influence of Pierre Léna by a cooperation of ESO, ONERA in Paris and some French observatories. In 1990 this instrument “COME-ON” was placed at the 3.6-m telescope. It had 19 actuators on the flexible mirror and was intended to give perfect diffraction limited images at 3.5 μm. With the completion of the VLT, a MultiApplication Curvature Adaptive Optics (MACAO) program was implemented to build seven AO systems for some instruments and for the VLT Interferometer3). An example of the results from one of the VLTI systems is shown in Figure VII, 1. Also for the high resolution camera CONICA a German-French collaboration has constructed the AO system NAOS with 185 actuators, which gives diffraction limited images at 2.2 μm. Even at 1.2 μm the system worked well with 0.04 arcsec resolution, probably the best reached so far by any telescope on the ground or in space! It remains a formidable task, however, to advance to full adaptive optics correction at visible wavelengths around 0.5 μm. Both the fast image analysis and the control of the flexible mirror still pose some problems. We have not yet mentioned another limitation of adaptive optics. The reference star which determines the corrections to be applied has to be sufficiently bright. But within the small isoplanatic patch of an object we wish to study, there may not be such a star. Artificial laser stars may be the answer. There are two options. In the high atmosphere, about 100 km up, there is a layer of neutral sodium. Higher up the sodium is ionized, lower down it is incorporated into molecules. When we shine a laser tuned to the wavelength of the strong sodium D line onto this layer, some of the light is scattered back, creating an artificial star. Alternatively, laser light in the blue part of the spectrum may be scattered by nitrogen or oxygen molecules. If the laser is

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Figure VII, 1. Adaptive Optics. To the left a star imaged in the K-band (2.4 μm) at a time the atmospheric seeing was 0.75 arcsec. To the right the same star seen after the adaptive optics system for the VLTI was switched on. The resulting image shows that the “star” is actually a close double star with a separation of 0.12 arcsec between the components. The first AO system at ESO was COME-ON implemented in 1990 at the 3.6-m telescope. Not only is a more detailed image obtained, but also the sharp peak of light allows fainter objects to be detected above the background.

pulsed and if we suitably select the time delay of the returning light, the altitude of the apparent laser star is also determined because of the finite velocity of light. Even though there are many complications, the advantage of the laser star is that by pointing the laser beam in the right direction, we can ensure that it is within the isoplanatic patch around the object under study.

Instrumentation Each of the four 8.2-m unit telescopes has two Nasmyth foci and one Cassegrain focus. So at these foci one may install 12 instruments which can remain in place for long times. In the past, at the 3.6-m telescope with effectively just one Cassegrain focus, multiple instruments were used. The frequent instrument exchanges caused much loss of time, since new calibrations had to be made each time an instrument was replaced, and because malfunctions were most frequent when another instrument was put in place. At the VLT, each instrument is permanently placed until a new instrument or an upgrade arrives. As a result, quality and efficiency have much increased. The only exception is the “visitor focus” where astronomers from the community may place an experimental – or a niche – instrument they have developed. The construction of instruments for the VLT is a major undertaking. So it was neither feasible nor desirable for ESO to build all the instruments in-house. Instead, with some exceptions, most have been contracted out (competitively) to institutes, or more usually consortia of institutes, in the

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member countries: ESO would provide the funding for the industrial hardware and the institutes would provide the necessary personnel. In exchange, the institutes would receive a specified amount of privileged observing time outside the normal time allocation channels. After this time has been used up, the persons who have participated in the building of an instrument still have the advantage of a better knowledge of its potential and therefore a certain advantage in the preparation of proposals for the normal time allocation process. The participation of many institutes in the instrument building has created a much stronger sense of participation in the VLT by the community and fostered European cooperation in multinational consortia. We note that the ESO procedures are different from those at ESA, where the total cost of instruments is (in principle) assumed by the institutes of the member countries and their space agencies; correspondingly, the return of privileged observing time is also larger at ESA. However, in the meantime the situation at ESO has become more mixed. To ensure uniformity, also in later maintenance and data handling, ESO has taken more responsibility for the area of detectors and associated electronics. On the other hand, hardware expenses have also sometimes been assumed by the national institutes to speed up the construction. And, of course, ESO staff always has a role in ensuring that the instruments can be properly integrated at the telescope. The total cost and effort involved in the instrumentation is quite large. For example, UVES built at ESO cost some 2.5 M€ in money and in addition 40 man/years of effort. For the MIDI interferometric instrument the consortium members invested 1.8 M€ in hardware and 4.2 M€ in personnel costs. I would estimate that in total the instrumentation cost for ESO and the national institutes to-date is some 20% of the cost of the VLT itself. This is not very different from the situation at ESA where the national payload support (for instruments) during the nineties amounted to 24% of the spending of the Science program, the latter essentially used to build and manage the satellites. When a few decades ago ESO received instruments from astronomical institutes, the quality sometimes was modest. Loose wires would be hanging around, electronic interfaces or components would be incompatible with La Silla standards and data handling software limited. The situation now has changed. Most instruments built so far are of the highest engineering quality, and only in two cases did ESO have to cancel a contract. The improved quality of the work of the institutes is in part the result of their participation in the space program. An instrument built for a satellite has to undergo stringent tests and to meet certain deadlines. If not, the satellite may leave without it. The resulting attitudes towards quality control have benefitted ESO and also the participating industries. The selection of the 11 facility instruments has been preceded by much consultation with the community. Some instruments have been functioning for six years, others have just been finished. At the same time, plans for

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second generation instruments have been made. In Figure VII, 2 and Table VII, 1 the instruments located at the four unit telescopes are identified. Around full moon the sky is too luminous to observe faint objects at visible wavelengths, but in the IR this is less of a problem. Also observations of brighter objects at very high spectral resolution are not much affected. So each unit telescope has at least one instrument in these categories. Six of the instruments are imagers. With filters broad or narrow wavelength ranges may be selected. The near IR imagers are provided with adaptive optics. Different angular resolutions may be obtained, with the corresponding field of view determined by the size of the detector. The better the resolution, the smaller the angular field of view. Even though it does not have a real adaptive optics system, ISAAC has yielded excellent images which

Figure VII, 2. The VLT and its instruments. From left to right, the four unit telescopes with their Mapuche names. UT1: Antu, the Sun; UT2: Kueyen, the Moon; UT3: Melipal, the Southern Cross; UT4: Yepun, Sirius. In front, the stations where the auxiliary interferometric telescopes may be placed. Schematically, the subterranean tubes are shown through which the light reaches the VLTI laboratory, which houses the delay lines (Figure VII, 7), the beam combiners and the interferometric instruments. Between UT3 and UT4 the 2.6 m VLT Survey Telescope, VST, is visible. VISTA is a 4-m IR survey telescope on NTT hill.

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Table VII, 1. Instruments at the VLT. The columns from left to right give the year of completion, the unit telescope and the focus Nasmyth or Cassegrain, the acronym, the wavelength range in μm, the characteristics with im for imager and the maximum spectral resolution for spectrographic modes, the largest field of view in arcminutes, the smallest number of arcsec per detector pixel indicative of the angular resolution and the eventual combination with adaptive optics, the maximum number of spectra taken in multiple object spectroscopic mode and the presence of an integral field unit (IFU) or of a long slit (ls), the number of pixels on the detector in units of a million, and a reference to an article in the ESO Messenger. It is important to note that the field of view is smaller if the angular resolution is high and that at high spectroscopic resolutions multiplicity of objects is smaller. For a more complete review of the instruments, the articles in the “Messenger” or the ESO web pages should be consulted.

Year

UT

Name

λ (μm)

1998 1999 1999 2002 2002 1998 2001 2004 2004 2004 2006 2007 2010

1C 2C 2N 3N 2N 1N 4N 4C 1N 3C N C N

FORS1 FORS2 UVES VIMOS FLAMES ISAAC NAOS-CONICA SINFONI CRIRES VISIR HAWK-1 X-shooter KMOS

0.3–1.1 0.3–1.1 0.3–1.0 0.4–1.0 0.4–1.0 0.9–5 1–5 1.1–2.5 1-5 8–25 0.9–2.5 0.3–1.9 0.9–2.5

max res im, 1800 im, 5000 115000 im, 2500 47000 im, 3000 im, 2000 4000 100000 im, 25000 im 7000 4000

max FOV (arcm)

min arcs/pix

MOS

Mpix

ref

7 7 0.2 15 25 2.5 1.2 0.13 0.8 1 7.5 0.2 7.2

0.1 0.1 0.5 0.2 0.5 0.15 0.013 AO 0.025 AO 0.1 AO 0.075 0.1 AO? 0.6 0.2 AO?

19 100 7 ls 1000, IFU 125, IFU ls ls IFU ls ls – ls IFU

4 4 16/8 8 8 1 1 4 4 0.06 16 8/1

a a b c d e f g h i j j j

References: a. ESO Messenger 94, 1, 1998; b. 99, 1, 2000; c. 109, 21, 2002; d. 110, 1, 2002; e. 95, 1, 1999; f. 107, 1, 2002; g. 117, 17, 2004; h. 114, 5, 2003; i. 117, 12, 2004; j. 115, 8, 2004.

frequently show very different features from those seen in the visible. In many heavily absorbing nebulae ISAAC can penetrate the absorbing dust and study star formation. Also interesting multicolor observations in the solar system may be obtained. In the case of Jupiter different wavelengths show different features because of the different absorption by methane and other molecules (Figure VII, 3). Particularly spectacular results on the center of our galaxy have been obtained with NAOS-CONICA (Figure VII, 4)4). In visible light it is unobservable because of very heavy interstellar absorption. However, in the near IR numerous stars shine through (left figure). One of these is extremely close to the radio source Sagittarius A* which is believed to be coincident with the black hole at the Galactic Center. In fact, repeated observations, first with

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Figure VII, 3. False color combination of several broad and narrow band images of Jupiter in the 3.2–4.1 μm spectral range. The auroral oval is well visible. The energetic particles which create the aurorae interact with the atmosphere and generate the “blue haze” which is spread around in longitude by the strong zonal winds.

Figure VII, 4. The Galactic Center imaged by NAOS-CONICA. To the left the orbit of the star (S2) closest to the radio source Sagittarius A*, which describes an elliptical orbit with 15.2 year period around it. This effectively demonstrates that Sag A* is coincident with the 2.6 million solar mass black hole at the Galactic Center. At the moment of closest approach Sag A* was hidden by the star. To the right are two exposures in the IR of the area of the Galactic Center taken later in 2002 after Sag A* became again observable. In the image at t = 0 no emission was visible at its location, but 39 minutes later (t = 39) it had erupted, presumably due to some matter spiralling into the black hole.

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the NTT and later with the VLT, have enabled to determine the highly elliptical orbit of this star around Sag A* (left figure). It has a period of 15.2 years and passed closest to Sag A* in April 2002 at a distance of about 0.015 arcsec or 17 light hours with a speed of 8000 km/sec. The origin of this star and others close by is baffling. But these results show the incredible power of a large diameter high quality telescope with Adaptive Optics. At the moment of closest approach Sag A* was hidden by the star. As this star began to move away, Sag A* became observable again. Hour long bursts of IR radiation were detected which were precisely coincident with this object. Also XMM-Newton (Chapter XI) has detected X-ray bursts from the area of the Galactic Center. However, its angular resolution is inadequate to prove that the X-rays come from Sag A*, though that is the most likely interpretation. A typical spectrograph consists of a slit through which the light enters, a dispersing element (prism, grism, grating), some further optics and a detector. With a relatively long slit the spectra of more than one star or of a slice of an extended object like a galaxy may be determined. But if, for example, we wish to measure the redshifts of the numerous faint galaxies in a field of view, it is unlikely that more than two or three will be located exactly on the slit. It is here that the Multiple Object Spectrographs (MOS) come in: numerous slitlets are placed in the focal plane at the positions of stars or galaxies to obtain their spectra. Two ways to do this are employed in the VLT instruments. The simplest is the metal mask with small slits cut in. First, an image of a certain field is taken and the positions of the objects of interest determined. Subsequently, the slitlets are cut at these positions. At first this was done mechanically, now a laser cutter is used which does this much faster. The most extreme MOS is VIMOS which allows up to 1000 slitlets in one go (Figure VII, 5). Of course, for each new field a new mask is to be made. The alternative is to use fiber optics. Small lenses coupled to optical fibers are mounted on arms so that they may be placed anywhere in the field. Through the fibers the light reaches the slit of a long slit spectrograph. In the case of FLAMES, 125 fibers allow 125 spectra to be stacked above each other. It is necessary to design the system of fibers so that they cannot collide or become entangled. An alternative type of spectrograph is the Integral Field Unit. Here a two-dimensional array of contiguous lenslets images a certain area. Subsequently, the light of all these lenslets is projected on a slit spectrograph. In the case of SINFONI, the array consists of 32 × 32 lenslets, and so 1024 spectra are taken at the same time. Thus, a star cluster or a galaxy can be completely analyzed all at once. At very high resolutions more conventional single slit spectrographs with échelle gratings have been constructed. In the échelle format different segments of the spectrum are stacked above each other on the detector. So a large stretch of spectrum at high spectral resolution can be obtained. In the case of UVES, the segments are separated by 12 arcsec and so there is

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Figure VII, 5. Some 220 stellar spectra taken simultaneously by VIMOS with a spectral resolution of 250. With VIMOS up to 1000 spectra may be taken at the same time.

space for the spectra of some other objects in between. A mode has been developed in which UVES at one Nasmyth focus of UT2 is coupled to FLAMES at the other focus with 50-m long fibers; this allows seven stars to be observed at the same time. Three new instruments are being planned. HAWK-1 will be an imager and KMOS an Integral Field Spectrograph, both for the near IR and both covering as large an area as possible. When adaptive optics on the secondary mirror are implemented (as on the LBT, Chapter V), this would further enhance the performance. X-shooter would be a spectrograph that allows simultaneous coverage of the visible and most of the near IR. Irrespective of the details of their construction, all spectrographs share a very much increased efficiency. Through mirrors or fibers the spectra are stacked in such a way that most pixels of the detectors obtain useful data; nothing is wasted. The VLT has become very much one integrated facility. Observers for all telescopes are located in the VLT control center. By activating remotely controlled mirrors, they may switch in seconds from one instrument to another and in each instrument between different imaging and spectroscopic modes. During routine observation, manual intervention on the spot should not be needed. Unless something goes wrong, it is not necessary to touch the instruments since they all have their fixed place. In fact, most observers need not see their telescope at all!

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Interferometry A high angular resolution requires a large telescope. However, it is not necessary that all of the mirror surface be covered with reflecting material. In fact, if a number of small reflecting areas are suitably chosen, much of the image resolution is preserved, but, of course, the light collecting power is diminished. If now these reflecting areas are mounted individually, the situation is no different. Hence, instead of building a 10-m telescope, one could build a number of 1-m telescopes and obtain a comparable angular resolution. This is the principle of the interferometer where light is combined from a number of independent telescopes scattered over an area large compared to the areas of the individual telescopes (Figure VII, 6). There is, however, one difference. In a single surface telescope the optical path length to different parts of the mirror is the same, no matter what the orientation of the telescope is. In two separately mounted mirrors this is no longer the case, and the path length difference depends on the direction of the object being studied. To compensate for this, “delay lines” are introduced which allow the optical path to the different telescopes to be equalized. Since the optical path length should be stable to a fraction of a wavelength, the delay lines represent high precision optomechanical systems (Figure VII, 7). Of course, the positions of the mirror surfaces should be equally stable. Vibrations of the telescope mechanics and of the soil on which they rest should be minimized. In interferometry the atmospheric turbulence is also a major obstacle and with large telescopes adaptive optics is essential. At the VLT the four telescopes have fixed locations, and this is insufficient to obtain complete interferometric images. To improve the situation, four mobile 1.8-m telescopes are being added to the interferometer, so that by positioning these in various places a better approximation to a large telescope may be realized. While in this way the image quality may approach that of a 200-m telescope, the limiting brightness corresponds to that of a 1.8-m telescope. Still the angular resolution of a milliarcsecond at 1 μm wavelength should allow very detailed observations of numerous interesting objects. Since the tolerances of the optomechanical systems are proportional to the wavelength and since AO is required, the VLT interferometer has been initially restricted to the nearer infrared. Observations at longer wavelengths are also foreseen, but since the atmosphere radiates rather strongly in the “windows” around 10 and 20 μm, even on as dry a site as Paranal, very faint objects cannot be observed. For most interferometry in the midand far-infrared space based interferometers are required. Both ESA and NASA are planning such interferometers, but the technological challenges are daunting. Several facility instruments are being constructed for the beam combination in the VLTI laboratory5): MIDI6) (2003) is a mid IR (8–13 μm)

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Figure VII, 6. Interferometry with two independent telescopes of the VLT array. Several flat mirrors bring the light beams from the moving Nasmyth focus to the stationary coudé focus. Since the light waves from a star will reach the two telescopes at variably different times, delay lines (essentially moving mirrors, see Figure VII, 7) are inserted to ensure that the optical path length remains the same. Then the two beams can be made to interfere in the Beam Combination Lab, resulting in an image composed of bright and dark stripes – the interferometric fringes.

instrument which combines the beams of two telescopes and provides a spectral resolution of 300. AMBER 7) (2004), a near IR instrument (1–2.4 μm), can combine three beams. This is important because then “closure phase” techniques (developed by radio astronomers) may be used which improve the image quality. It provides spectral resolutions of 10,000.

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Figure VII, 7. The VLT interferometric tunnel with the delay lines. These have to be extremely straight and accurate to ensure that differences in optical path length remain much less than one wavelength.

In 2005 the near IR instrument PRIMA should arrive. While the drawback of the other instruments is the small field of view (2 arcsec), with PRIMA two such fields separated by up to an arcminute may be observed simultaneously. With a star in one field as a reference, the positions in the other may be determined with a relative accuracy of 10 microarcsec. This is particularly interesting for planet searches (Chapter XV). An experimental instrument, GENIE, is being developed in an ESA-ESO collaboration, which is to serve as a prototype for the Darwin nulling space interferometer aimed at finding earth-like exoplanets (Chapter XV). Much indirect evidence has led to a picture of active galaxies in which a black hole nucleus and its environment are surrounded by a dusty absorbing torus which would generally be too small to be directly observed. With MIDI for the first time a glimpse of such a torus has been obtained at 10 μm wavelength8). Emission from warm dust at about 320 K temperature was detected from a region with dimensions of only 7 × 13 light years around the nucleus of the well known Seyfert galaxy NGC 1068. This result shows the great potential of the VLTI. Further upgrades would appear to be justified.

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Survey Telescopes In the past, Schmidt telescopes were used to photograph large parts of the sky. These allowed interesting objects to be found for more detailed studies with the larger telescopes. However, the photographic plates did not reach very faint objects. Even though the fields that may be surveyed are much smaller, the depth and accuracy reachable with CCD detectors have led to the closing of many Schmidt telescopes, including the 1-m at La Silla. Still large scale surveys remain important. A 2.6-m VLT Survey Telescope has been built by the Capodimonte Observatory in Napoli to be placed at Paranal. Unfortunately, during transport to Chile the mirror has been destroyed. A new mirror arrived in 2004. The VST has a CCD camera with 256 million pixels9), allowing it to image one square degree with a resolution of 0.22 arcsecond. An observation of 4 hours through five filters should reach quite faint objects (25th magnitude). However, it still would take half a century to survey the whole southern sky, and so suitable areas have to be selected. The quantity of digital data generated will be enormous. A 4-m survey telescope, VISTA, is being built by the UK at a cost of 51 M€ and will be transferred to Paranal in 2007 as part of the entrance fee the UK had to pay as a compensation for the investments made earlier by ESO. VISTA should make surveys in the near IR to 2.4 μm with a 64 million pixel camera. Its enclosure is being built on the “NTT Hill” (Figure VI, 7).

The Virtual Observatory The incredible data flow coming from the world’s optical, radio and space based observatories necessitates the implementation of suitable archiving procedures. In the past observatories archived their photographic plates, and when a scientist was looking for a particular item there generally was someone who could locate it in a plate catalog or from memory. With the expansion of the number of instruments and their increased efficiency, this is no longer possible. Moreover, if every institute decided on its archival format, access would be difficult. So it is important to make the archives follow certain rules and also to ensure that one can conveniently discover what has been done before. Hence, the International Virtual Observatory Alliance which manages the Virtual Observatory. The European version of it is the Astrophysical Virtual Observatory. The AVO has as partners ESO, ESA, Astrogrid (UK), the Institut d’Astrophysique, the Université de Strasbourg, Jodrell Bank Observatory, and the Centre de Données Astronomiques de Strasbourg which in Europe pioneered data archives. The AVO is partly funded by the EC. Once the system is complete, it should become very easy to combine different data sets. As an example, ultimately one should be able to superpose on a VLT image the X-ray sources that will be detected by the Japanese ASTRO-E, the IR sources found by NASA’s Spitzer and also to find all the available spectroscopic data for these objects. For the VO to be fully useful, it will be important to include only fully validated data.

VIII. Ground and Space Based Optical Telescopes

By sparing neither labor nor expense, in constructing for myself an instrument so superior that objects seen through it appear magnified nearly a thousand times … Galileo Galilei1)

HST In 1946 Lyman Spitzer described the great advantages that could result from placing a large telescope in space. Not only would this give access to the ultraviolet, hidden from our view by ozone in the stratosphere, but it also would eliminate the deleterious effects of atmospheric turbulence on image quality in the visible part of the spectrum and the effects of the faint atmospheric airglow. Years later, in 1971, NASA would initiate planning for building the Large Space Telescope, which finally resulted in the 2.4-m Hubble Space Telescope. In 1979 the total cost of the program to NASA was estimated at 440 MUS$2) (equivalent to 1000 M$ in 2004 value), including 90 M$ for designing, building and testing the scientific instruments. The telescope was to be launched late in 1983 by the Space Shuttle into Low Earth Orbit, which would make it possible to visit it again at a later date to make repairs or upgrade instruments. In those days of shuttle optimism visits every 2–3 years by astronauts and a return to earth and relaunch every 5 years were envisaged3). Five instrument locations were foreseen, four of which would be occupied by a wide field imager, a low and a high resolution single aperture spectrograph and a high speed photometer (Table VIII, 1). The launch of HST took place in April 1990, following a long delay due to an earlier shuttle accident. In 1977 ESA joined the project as a 15% partner; it would provide the fifth instrument, the Faint Object Camera (FOC), the solar panels and a contingent of some 15 scientists at the Space Telescope Science Institute (STScI) in Baltimore. In return, European scientists could apply for observing time on all instruments with a guarantee of at least 15% of the total. Actually European principal investigators obtained about 19%.

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Table VIII, 1. Instruments at HST and foreseen for its successor JWST. From left to right the columns give the acronyms, the years of operation, the principal functions (imaging, spectroscopy, high speed photometry), the wavelength range, the spectral resolutions and the field of view. Spectral resolution may be obtained for all objects in the field with filters (f), grisms (prism with on one of the surfaces a grating so that at the central wavelength the position of the spectrum and the direct image are coincident) (g), prisms (p) and in addition for selected objects from spectrographs with slits; grisms have typical resolutions of the order of 100, while the STIS prism has a resolution ranging from 26 at 0.32 μ to 1000 at 0.12 μ. The spectral resolution range is not necessarily available over the whole wavelength range. Several imagers also have higher angular resolution cameras with smaller FOV’s.

WFPC1) FOC1) FOS GHRS HSP STIS NICMOS ACS NIRCam NIRSpec MIRI

years 1990-2007? 1990-2002 1990-1997 1990-1997 1990-1993 1997-2004 1997-2007? 2002-2007? 201120112011-

HST instruments wavelengths spectral function (μm) resolution im 0.12–1.1 f im/sp 0.12–0.6 f, g, 1000 sp 0.12–0.8 250, 1300 sp 0.12–0.3 20000, 90000 hsph 0.12–0.8 f sp/im 0.12–1.0 f, p, 400–100000 im/sp 0.8–2.5 f, g im 0.12–1.0 f, g JWST instruments im 0.6–5 variable f-100 sp 1–5 100–3000 im/sp 5–27 f, 100, 3000

FOV (arcsec) 3 × 75 × 75 7×7 0.3 0.3 50 × 50 50 × 50 200 × 200 140 × 280 180 × 180 100 × 100

1)

Data for WFPC 2 (1993) which was adapted to the telescope optics and for FOC + COSTAR (1993). FOC also had a less used 14 × 14 arcsec camera.

The FOC was to be the imager with the highest angular resolution. It also contained a spectrographic mode which allowed long slit spectroscopy. While the two other spectrographs could only obtain a spectrum at one point, the FOC could also study spectral variations at different points along the slit. The FOC was a very complex, but powerful instrument, though it could only image a rather limited field. Larger fields were the domain of another instrument, the Wide Field and Planetary Camera (WFPC). The Space Telescope Science Institute was to ensure that the instruments functioned optimally and that the users of HST could obtain all the necessary information and assistance. It also was responsible for organizing

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the time allocation process. The 15 ESA scientists were rapidly fully integrated into the institute staff and fulfilled a useful role for the project in general and the European users in particular. However, there remained a concern that the European scientific community was insufficiently prepared to make effective use of the HST and to submit competitive observing proposals. So it was decided by ESA, following some pressure from the scientific community, to have a small group in Europe devoted to HST operations – the ST/ECF, the European Coordinating Facility for the Space Telescope. It was to promote awareness of the potential of HST, information for prospective users and assistance with the analysis of data when needed. The ECF was foreseen as a cooperative venture between ESA and a host institute of high scientific quality. ESO and a few other European institutes responded to ESA’s Announcement of Opportunity. While it was perhaps unfortunate to have ESO in competition with institutes in its member countries, it was also clear that it was the most suitable organization from many points of view. The services which ESO already provided to scientists in the member countries were of the same nature as those required for HST. Thus, in 1983 an agreement was concluded between ESA and ESO for the joint operation of the ECF at ESO in Garching. This first significant agreement between the two organizations has had a very positive effect on the development of European astronomy, in particular in the areas of image processing and archiving, but also more in general in bringing ground and space based astronomy closer together. The excellent cooperation between the ECF and the STScI in Baltimore was essential to the success of the former and beneficial to the friendly relations between the European and American astronomical communities. It should be noted that the creation of the ECF did not give full equality to European scientists. After obtaining data from HST, funds for equipment and assistants needed for the analysis had to be applied for nationally by the investigators. The American scientists generally obtained NASA funding immediately after they had been awarded the observing time. On April 24, 1990 HST was launched. Soon thereafter it was discovered that the primary mirror had not been figured according to specification, owing to an error in testing. As a result, it did not fit very well to the secondary and the image quality of the telescope was degraded. While this was reducing the effectiveness of all instruments, it was particularly damaging for the FOC which had been specifically designed to obtain the very highest possible resolution. Following months of intensive analysis and consultation, it was decided to construct corrective optics (COSTAR) for the FOC and the spectrographs, and to build a new WFPC, optically adjusted to the characteristics of the primary mirror. During a visit by the shuttle in December 1993, the old WFPC was replaced and the high speed photometer taken out to make room for the correcting optics. However, by that time the FOC had developed some electronic problems which somewhat reduced its usefulness.

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Three further shuttle missions to HST took place in February 1997, December 1999 and February 2002. During the first one the two spectrographs were removed and replaced by a much more powerful Imager/Spectrograph STIS optimized for the ultraviolet, and a Near Infrared Camera and Multiple Object Spectrograph (NICMOS) which extended the spectral range of HST to 2.4 μm. The NICMOS detectors had to be cooled, but the block of solid nitrogen evaporated faster than foreseen. The 1999 mission was for repairs, maintenance and orbital lifting. In the 2002 shuttle visit a mechanical cooler was installed which brought NICMOS back to life. The FOC was removed and replaced by the Advanced Camera for Surveys. From then on there was no ESA hardware on HST, but the ESA contingent continued its work in Baltimore, while ESA and NASA were negotiating a new agreement which also included a 15% share in the successor telescope JWST. Plans were being made for one or two additional refurbishment missions, but for the moment the second shuttle accident put an end to these. Since HST needs an orbital lift from time to time, this would imply that it may end its life in 2007 or 2008, unless pressure from the US scientific community and the general public causes NASA to change its plans. In the meantime STIS failed with little chance of it being revived. Also proposals have been made for a robotic repair mission at such a high cost that other future missions might have to be significantly delayed. ESA’s participation in HST has been very much worthwhile for the European scientific community. The total cost to ESA in 2004 euros has been of the order of 600 M€. The overall cost of the whole HST project including operations may be estimated at 6 G$, with the largest items five shuttle flights and 18 years of spacecraft operation. In round numbers this corresponds to a million US$ per day. It has frequently been said that the HST experience demonstrates the usefulness of manned space flight. True enough, without the shuttle visits it would have been impossible to make the repairs and instrument exchanges. But the telescope was more expensive than it could have been because it had to be safe for human intervention, while the cost of the shuttle flights far exceeded that of the telescope itself. Moreover, the low earth orbit required for shuttle access was operationally expensive and scientifically far from optimal. In fact, less than half of the total time could be used because of earth occultation effects. Probably for the same amount of money, three or perhaps more STs could have been built and placed into better orbits with conventional rockets. It is also true, however, that it might have been difficult to maintain the political support for such a program, while the glamor of the various visits by astronauts has benefitted the overall space program. In the future when telescopes are placed at L2, beyond lunar orbit, robotic repair missions might be needed. However, some thought is also being given to the development of a more suitable vehicle for astronauts to go there.

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HST and VLT The question has been asked, why we still should build the VLT when the Hubble Space Telescope provides such beautiful images of celestial objects which are unsurpassed by telescopes on the ground? Alternatively one could ask, why, with the VLT having such superior light gathering power, would we still build a successor to HST in space? The answers are partly scientific and partly economic. At some wavelengths the atmosphere is opaque and observations are only possible from space. But when both space and ground based observations are feasible, the latter are much cheaper. For the same amount of money a more powerful instrument could be constructed on the ground. Hence, what can be done from the ground, should be done there. New technological developments, in particular adaptive optics, are dramatically changing the capabilities of ground based telescopes. But also space telescopes could improve their performance by moving out of low earth orbit. So the balance between the two has to be revisited and the answers that were given some decades ago may no longer be valid. Let us first compare the cost of collecting a certain amount of light with the VLT and the HST. The four 8.2-m telescopes of the VLT with their instrumentation will have cost some 1000 M€ after 17 years of operation. This figure includes personnel costs at ESO and in the institutes of the member countries which are contributing instrumentation. The cost of HST is more difficult to estimate, but in the preceding paragraphs we found a figure of the order of 6000 M$ if the costs of the shuttle flights for maintenance and upgrading of instrumentation are included. In the further discussion we shall take euro and dollar as equal, which is appropriate as an average over the last decade. The 2.4 m HST has a light gathering surface 47 times smaller than the VLT. Since in visible light the atmosphere absorbs or scatters on average some 10% of the incoming light, the effective light gathering power of HST is 42 times smaller than that of the VLT. One more factor needs to be taken into account: the annual amount of observing time. Even at Paranal, the world’s most favorable site for low cloudiness, some 15% of the time is lost or not very useful. Of the remainder the sun is up half of the time, and the percentage of real dark time is only 37% of the 24 hr day. Thus, finally only 31% of the total time can be used. In the visual part of the spectrum the full moon makes some observations difficult or impossible, but in the near IR the situation is more favorable. Also spectroscopic work at high resolution is not much affected. So we shall neglect the lunar problems in the comparison. We have seen that HST in its low earth orbit has an effective observing time about half of the total or less. With HST being six times more expensive and having an effective light gathering power some 42 times smaller than the VLT, we conclude that the cost of detecting a certain amount of light is some 150 times higher for HST.

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However, this is not the whole story. When we observe very faint objects, we become less efficient because the diffuse background light may exceed the light received from the object under study. This background light may be due to the earth’s atmosphere, to the zodiacal light resulting from the scattering of light from the sun in interplanetary space and to sources further away. Eliminating the terrestrial component of the diffuse background light, we roughly halve its intensity in the visual part of the spectrum. A further important factor is the angular resolution. Without adaptive optics at the best sites a stellar image on the ground is spread out over some 0.6 arcsec by atmospheric turbulence. As a consequence, more background light is sampled than in the case of HST where the image spread is closer to 0.1 arcsec. If the brightness of the background underlying the image of a star is much larger than the brightness of the star, the latter is determined by subtracting the background from the image of star + background. Since these then are nearly equal, a very precise determination is needed so that the difference may be established sufficiently accurately. In practice this means that the amount of time needed to observe a faint star is multiplied by l’/l where l’ is the brightness of the background underlying the image and l that of the star. Thus, if we observe a star 100 times fainter than the background, we have to spend a 100 times longer time than in the absence of a significant background to obtain a (statistically) equally precise result. So the cost advantage would be reduced correspondingly. Furthermore, the background under the stellar image may include sometimes unresolved faint stars which may cause the observation of the target star to be in error. With the better resolution of HST that risk is smaller. Moreover, time variations and inhomogeneities in the atmospheric night glow provide intrinsic limitations to the accuracy with which stellar brightness may be measured from the ground. The conclusion is that for very faint stars the HST has a qualitative superiority. For the moment HST is the telescope of choice to reliably detect the faintest stars in visible light. The situation is modified by adaptive optics, but it is difficult to make quantitative predictions. Since the intrinsic resolution of a diffraction limited 8.2-m unit telescope is 8.2/2.4 times better than that of HST, the effects of the background would be drastically reduced if full compensation for atmospheric turbulence could be obtained. Then we would sample the background under the stellar image over an area of only (2.4/8.2)2 times that with HST. Even for faint objects the advantage would be overwhelmingly in favor of the VLT. However, existing adaptive systems work only in the IR; AO is much more difficult in the visible. Moreover, such systems tend to concentrate part of the light in a sharp central peak, but some remains in a more diffuse image. So the gain is certainly not as large as a simple minded calculation would indicate. The photometric precision obtainable with AO also remains to be explored.

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HST and VLT are complementary. Because of the exquisite angular resolution HST is the most suitable for detecting objects much fainter than the background. But because it is rather small it does not collect enough light to obtain a spectrum that could show the nature of faint objects. For this the VLT with its large light collecting power is much more suitable. So the combination of the two is producing results that could not have been obtained with each telescope alone. In Figure VIII, 1 are shown the time needed to observe stars of a given visual magnitude with HST, a VLT unit telescope, with and without adaptive optics, a 40-m telescope and the 100-m OWL, both with AO. The curves are for a measurement with 10% accuracy, for a total efficiency (throughput) of the optical system of 1/3 and for a 0.1 μm wide segment of the spectrum. If the desired accuracy is a times better, if the throughput is b times smaller and if the spectral segment is c times narrower, the time needed becomes a2 × b × c times longer.

JWST and OWL HST and VLT have been immensely successful and continue to generate a high quality data stream on the widest variety of objects in the Universe. Both have stretched financial resources almost to the breaking point. Should we then consider these two as the endpoint of telescope development in space and on the ground or are they just an intermediate stage to be followed by even more powerful instruments? In 1995 HST was pointed to the same area of the sky for ten days. The result was the “Hubble Deep Field” image in which numerous faint galaxies are visible. Three years later followed the southern counterpart the “HDF-S”, where many spectra have been obtained with the VLT. With the new ACS an even deeper “Hubble Ultra Deep Field” was completed in 2004 (Figure VIII, 2). But even in these deep fields the faintest but intrinsically bright spiral galaxies (similar to our own or the Andromeda Nebula) have redshifts not much larger than z = 1. However, most galaxies must have formed at redshifts of perhaps z = 4–6 or even more. So we still have sampled only a small part of the Universe, and our direct knowledge of the formation and early evolutionary phases of galaxies like our own is very slight. It is, of course, true that already we now see the most luminous galaxies or quasars at redshifts up to z = 6. But these are only rare very bright objects. It is as if in a forest we would only see the tallest trees, while the thousands of others escape our view: we would know very little about the ecology of the forest as a whole. HST has had only a limited capability in the near IR. But when we look at galaxies at a redshift z = 6, all wavelengths have been shifted by a factor 1 + z = 7. Thus, spectral lines which we observe in our Galaxy at 0.6 μm are displaced to 4.2 μm, well into the IR. The first galaxies must have formed

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Observing time in powers of 10 (s)

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Magnitude of a star at intermediate ecliptic lattitude Figure VIII, 1. The sensitivity of HST —, VLT unit telescope with AO — and without AO •••, a 40-m on the ground with AO — , and OWL —. Along the vertical axis is the observing time in powers of ten in seconds and on the horizontal axis the V magnitude of a star at intermediate ecliptic latitude, with 5 mag. representing a factor of 100 in luminous flux. The curves presented are based on the observation, with 10% accuracy, of a 0.1 μm wide spectral band centered at 0.55 μm with a telescope/instrument combination with throughput of 1/3. Note that at present no full adaptive optics system in the visible has been built. However, AO in the near IR is currently being implemented at the VLT. The relative shapes of the curves at 1 μm would not be very different. The curves with AO are drawn on the assumption that only half of the light is in the corrected image.

even earlier, and to obtain cosmological information a telescope optimized more towards the IR seems required. Since the angular resolution becomes poorer in proportion to the wavelength, it is important that the telescope mirror be as large as possible. Such considerations led NASA to the planning for the Next Generation Space Telescope, in which European scientists were also involved. The diameter of the NGST started out at 4-m and then, because

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Figure VIII, 2. Part of the Hubble Ultra Deep Field with a total HST exposure of 1 Msec.

of the enthusiasm of the head of NASA and the optimism about “faster, cheaper, better”, was doubled to 8-m. Equally optimistic industrial studies suggested a cost of some 1000 M$. Following the loss of some Mars missions, the “faster, cheaper, better” philosophy lost some of its glow, while industry became more cautious in its cost estimates when firm contracts were to be signed. So gradually the diameter shrunk and the cost went up to become 1600 M$ for a telescope with a collecting surface of 25 m2, equivalent to that of a 5.6-m diameter telescope with a circular mirror. To this were added contributions by ESA and Canada, bringing the total project cost to around

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Figure VIII, 3. The sensitivity of JWST and OWL. The two lines show the lowest flux that can be detected at 10% accuracy in 100,000 sec for a star at the ecliptic pole in spectroscopy at a resolution of 50; 1 Jy = 10-26 watt m2 Hz-1. In blue is the model spectrum of a primeval dwarf galaxy at a redshift z = 10, with a million solar masses in an active star forming phase which leads to strong hydrogen and helium emission lines at an epoch when heavy elements had not yet been synthesized. Many such galaxies may have been later incorporated into bigger systems. A comparison between JWST and other mid-IR missions is given in Figure XI, 7. The OWL curve is only applicable in the IR windows.

2000 M$. Past space missions had frequently the names of famous scientists (Hubble, Einstein, etc.) or mythological figures (Ulysses), but before many people were aware of it and without consultation, NASA named it after an earlier Administrator, James Webb, and NGST became JWST. JWST4) (Figures VIII, 3, 4) is to be launched with an ESA provided Ariane V rocket and placed at L2, the second Lagrangian point, some 1.5 million km from earth in the antisolar direction. Around L2 quasi stable orbits of spacecraft are possible which may be maintained with a very small expenditure of gas. The great advantage of a telescope placed at L2 is that the view is not restricted by earth occultation, and so almost all time may be used for observation, rather than the 50% in low earth orbit. Moreover, with Sun, Earth and Moon all in more or less the same direction, their IR radiation is far less troublesome than it was, for example, in ISO.

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Figure VIII, 4. Layout of the JWST5). Since the telescope is to operate in the near and mid-IR, a large shield protects it from heat sources. The primary mirror of 25 m2 area is made of light weight beryllium petals that will be deployed in orbit. The light reflected by the petals reaches the secondary mirror which reflects it back to the science instruments. The surfaces above the sun shield are covered by special coatings which allow the telescope to radiate heat efficiently into space and so reach temperatures around 30 K, necessary for the mid-IR observations. Below the shield are solar panels, communication equipment and some electronics.

Since a 6-m telescope cannot be fitted into the launcher, the primary mirror will be composed of 18 segments (made of beryllium for low weight) that will be deployed to form the mirror surface once in orbit. Also the secondary will be placed in position at that time. An active optics system will ensure that the telescope is diffraction limited at 2 μm wavelength. To avoid strong radiation from the telescope itself, it will be cooled to around 30 K. The cooling will be passive, with special coatings favoring heat loss by radiation into space, while minimizing radiative heating by an effective sun shield. JWST should be equipped with three instruments which cover the wavelength range 0.6–28 μm: NIRCam, a wide field camera covering 0.6–5 μm in wavelength, NIRSpec, a multiobject spectrograph for the range 1–5 μm, and MIRI, a camera-spectrograph for the mid IR range 5–28 μm (Table VIII, 1). NIRCam will be a NASA responsibility, while Europe will provide NIRSpec. MIRI will be a joint US – European undertaking.

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Canada will also participate in the project with the “Fine Guidance Sensor” which will ensure the continuous precise pointing of the telescope, and which also has an astrometric capability. JWST should be diffraction limited upwards from 2 μm, HST from 0.6 μm. Below these wavelengths the angular resolution does not change, because it is determined by the imperfection of the fine structure of the mirror surface. With the diameters differing by a factor of 2.5, the two should have the same angular resolution at 0.8 μm, but JWST will collect nearly six times as much light. So a deep JWST field may show even more numerous remote galaxies than the deepest HST fields. Some of the very faintest galaxies or quasars seen by JWST may be at large redshifts, but to be sure it is necessary to take their spectra. Because in a spectrum the light is spread out over many pixels, a larger telescope would be needed. This is one of the numerous motivations for constructing Extremely Large Telescopes (ELTs), the largest of which would be OWL6) (Figure VIII, 5), the OverWhelmingly Large telescope, a 100-m behemoth, currently under study at ESO. The projected cost is some 940 M€.

Figure VIII, 5. Artist impression of sunset over OWL. The 100-m spherical primary mirror is visible low down. The secondary is in the upper left, and the complex central structure contains additional mirrors. The mechanical structure is made from sets of identical components for cost reduction; also the mirror is a composite of identical segments. To the left are the rolloff roof for protection during the day and a smaller structure containing instruments.

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Mechanically there does not seem to be an unsurmountable problem to construct a 100-m telescope. After all, radio telescopes of such a size have been constructed before. However, with the wavelength for an optical telescope being more than a thousand times smaller, the tolerances are proportionally more rigorous requiring highly sophisticated controls. It hardly seems possible to effectively protect such a telescope from the wind by a building, since it would need an opening quite a bit larger than 100 m. So, like the radio telescopes, it would operate in the open air and undergo significant wind stresses which have to be compensated. To protect the telescope from storms and rain, a rollover structure is needed. In principle, the optics also seem to be feasible. However, several issues remain open. One proposal is to have a spherical primary, with a cost advantage in polishing. But the consequence is the need for a more complex image correction, requiring in one design six mirrors in total, causing significant light losses at visible wavelengths. The main unsettled issue pertains to the adaptive optics. The power of a diffraction limited 100-m telescope is largely due to its angular resolution and the consequent reduction in sampling background light. But this requires a very effective suppression of atmospheric image diffusion. It is necessary to deal with more than one atmospheric turbulent layer (multi conjugate AO). In fact, it is estimated that half a million active elements would be needed to achieve this at visible wavelengths. Since at present adaptive optics is beginning to be operational at 8-m telescopes only in the near IR where the tolerances are much more relaxed, it will be some time before such a system can be demonstrated. It is perhaps an interesting question if chaotic behavior may arise if the system becomes too complex. Since much of the science for OWL would be in the infrared, it might perhaps be acceptable to start with an AO system at 1 μm, especially if there were a reasonable prospect of extending it later to shorter wavelengths. The power of OWL would certainly be impressive. Cepheid variables for direct distance determination of galaxies could be measured nearly till a redshift z = 1, and so the global Hubble constant for the Universe could be obtained directly. Every type I supernova that has exploded in the Universe could probably be observed – and probably the same is the case for most type II’s (exploding very massive, young stars) which are intrinsically fainter, but relatively strong in the uv. The type I could possibly give a very clear picture of the geometry of the Universe, while type II would inform us about star formation and element synthesis history from very early time onwards. Quasars could be observed to high redshifts at sufficient spectroscopic resolution to see the absorption of intergalactic gas even at low density and to study its dynamics. The formation of galaxies would come within our reach. More in our immediate neighborhood very faint neutron stars could be observed. The center of our Galaxy could be studied in exquisite detail, and so could star and planet forming processes. Perhaps it could even be possible

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to obtain spectra of earth-like planets. And, of course, anything detectable by JWST in the optical and near IR could be studied spectroscopically by OWL. The principal limitation of OWL is the inaccessibility of much of the mid-IR. It would most effectively function in the range of 0.4–2.4 μm. At a redshift z = 9 this would correspond to the (far) uv for the emitted radiation. Some observations might be possible in the 10 μm and 20 μm windows, but because of the background due to the atmosphere and to the warm telescope the sensitivity would fall far short of that of JWST, at least for the faintest objects. But for higher resolution spectroscopy it would be superior. The cost of OWL is still very uncertain. Three decades ago the rule of thumb was that the cost of a telescope varies as the diameter to the power 2.6. With the 16-m equivalent VLT having a capital (industrial) cost (excluding VLTI and instrumentation) of 300 M€ (2004 value), OWL would come in at 32,000 M€! However, the VLT has shown that the situation is much more favorable than this. The NTT and the VLT have been built in rather similar ways. The industrial cost of the NTT (updated to 2004) was around 18 M€. In comparison with the VLT cost, this shows a variation with d1.8 rather than d2.6. So a larger mirror area has become cheaper on a per m2 basis – at least in this example. Nevertheless, scaling this way the cost of OWL would still be nearly 8000 M€. The cost of the NTT was some three times lower than that of the 3.6-m telescope at the same diameter. This was possible because of improved technology. The challenge for OWL is greater. Whether its cost can be brought down a further factor of 10 per unit area remains to be seen. Initial industrial studies are encouraging. The conclusion of the foregoing is clear. The OWL project is well worth detailed design studies. Before it can be built, three essential questions need be answered: (1) Is it possible to build the active optics system required for its diffraction limited performance, and at what wavelengths can it operate? (2) Can the cost be brought down to an acceptable level? (3) What is an acceptable cost level? More modest proposals for ELTs are under study in several places. At the 2003 meeting of the International Astronomical Union no less than nine proposed projects in the 16–50 m class were reported, though not all of them of equal realism. Sweden (Lund University) and institutes in SF, Ei, ESP and the UK are designing EURO 50, a straightforward 50-m telescope with a mirror composed of 618 segments at an estimated cost of 600 M€7). A USCanada cooperation is designing the TMT, a 30-m segmented mirror telescope, while another US group plans to build the GMT, a 21-m multimirror telescope with seven 8.4-m mirrors, corresponding to a collecting area 1.8 times that of the VLT. So if Europe would rest too long on its VLT laurels, it could soon lose its first place. The siting of these telescopes is still an open question. For Europe there seem to be two plausible options: La Palma or northern Chile. In both good

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seeing conditions prevail; the latter has the advantage of a very dry atmosphere, but the drawback of being more earthquake prone. There remains one problem not addressed by either OWL or JWST, the access to the ultraviolet. Once HST will have been terminated, there will be no uv telescope left. It had been foreseen to install at the next shuttle mission to HST the Cosmic Origins Spectrograph with a powerful uv capability. It has been built at a cost of 90 M$, but if no further refurbishment of HST is made, this very expensive instrument will remain in storage. In the Russian “Spectrum” series there were plans for “Spectrum uv”, a 1.7-m telescope of which some parts have been made. Lack of funds has prevented its completion. Some scientists in the community wish to revive this project (sometimes as a “world space observatory”), but no plausible sources of funding have been identified. Some smaller uv telescopes have been launched by NASA: FUSE8), a spectroscopic satellite for the 0.09–0.12 μm spectral region (with French participation) in 1999 and the Galaxy Evolution Explorer9) in 2003. With its 50 cm telescope it is making a sky survey in the uv. The Indian satellite ASTROSAT, scheduled for launch in 2008, will have two 38-cm uv telescopes for observations in the 120–300 nm domain.

Astrometry Atmospheric effects also limit the precision of the determination of stellar positions. In addition to the image diffusion by seeing, refraction in the atmosphere creates further problems. These may be overcome in case relative positions of not too widely separated stars are measured. If absolute positions over the whole sky are needed, the fitting together of results from observatories with access to different parts of the sky becomes difficult. The only really satisfactory solution is to go into space. In 1989 ESA launched the Hipparcos satellite. The spinning satellite registered the times at which 100,000 stars transitted over its detector. It was a major effort from these data to determine the positions of all of these. The satellite continued to observe for four years. Thus, it could also measure changes in position and so obtain annual parallaxes, due to the motion of the earth around the Sun, from which the stellar distances immediately follow. From the distances the physical properties of the stars, like the luminosities, may be obtained and stellar models thereby refined. Also the proper motions – the real displacements over the sky – could be obtained which is of interest in studies of the dynamics of our Galaxy. Hipparcos obtained positions with a precision of about 1 milliarcsec, yielding stellar distances out to a few thousand light years. The success of the mission led to various proposals for a follow up: at NASA FAME and in Germany DIVA, with the aim of an improvement of an order of magnitude

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in precision. In the meantime, both have been cancelled. ESA is planning GAIA – Galactic Astrophysics by Imaging and Astrometry – which should be launched in the 2010–2012 time frame10). GAIA should obtain results a hundred times more precise for 10,000 times more stars than Hipparcos (Table VIII, 2). Distances should be measurable through most of our Galaxy, allowing a full three-dimensional picture to be obtained of the whole system. Spectral distributions should also be measured for all stars and radial velocities for many. Very accurate motions should be obtained for many millions of stars. This should lead to a determination of the gravity field in the Galaxy and thereby also of the distribution of dark matter. GAIA will undoubtedly be quite important in studies of stars and of the dynamics of our Galaxy. GAIA should also detect half a million quasars, of interest for establishing a cosmological reference frame, 100,000 supernovae, 30,000 exoplanets and numerous asteroids and trans-Neptunian objects. It also should measure the gravitational bending of light by the Sun with high accuracy. It follows a European tradition of the study of large statistical samples in astronomy. Table VIII, 2. Comparison of Hipparcos and GAIA, two ESA astrometric missions.

Faintest magnitude Complete till magnitude Number of stars Precision in μarcsec Orbit

Hipparcos

Gaia

12 7 120 000 1 000

20 20 1 000 million 4 (at mag 10) 10 (at mag 15) 200 (at mag 20) L2

earth

In 2005 new complications surfaced11). The manufacturer of the JWST demanded a substantial extra payment, and with other items this caused a cost overrun of nearly a 1 000 million US$. So now there are proposals to further reduce the size of the mirror, to restrict the wavelength range and to limit the lifetime to 5 years. If these were to be implemented, it would be advisable for Europe to reconsider its participation. Joining the Japanese SPICA mission (Figure XI, 7) might be and attractive alternative.

IX. Radio Astronomy; ALMA and SKA

At length a universal hubbub wild Of stunning sounds and voices all confused Borne through the hollow dark assaults his ear John Milton1)

Visible radiation constitutes only a very small part of the electromagnetic spectrum, while most of the IR and X-rays are unobservable from the ground because of atmospheric absorption. However, radio waves can penetrate the atmosphere at most wavelengths from around 1 mm to 30 m, where the ionosphere provides a barrier. Radio Astronomy2) was born in 1932 when Karl Jansky at Bell Telephone reported his discovery of a mysterious source of radio noise which waxed and waned with sidereal rather than solar time. So the source had to be located outside the solar system. Subsequently, his data at 15-m wavelength showed that the strongest signal came from the area of the sky where the center of our Milky Way Galaxy is located. Since no radiation from the Sun had been observed, this could hardly be due to the accumulation of stars at the center. Actually, the radiation is “synchrotron radiation” due to energetic relativistic electrons gyrating in interstellar magnetic fields. Such radiation nowadays is well known in terrestrial synchrotrons where it is used to generate intense sources of light for the study of materials and biological structures. Since the magnetic fields in the interstellar medium are very much weaker, the Galactic emission emerges largely at radio wavelengths. In the meantime, a whole high energy universe has emerged, complementary to the visible universe of stars. Synchrotron radiation has been observed in stars, galaxies (Figure IX, 1), quasars and prodigious amounts of energy have been involved in the acceleration of these electrons. In our Galaxy the energetic electrons responsible for a large “halo” of radio emission are part of the cosmic-rays (Chapter XIV), and the study of the two has become very much intertwined. At decimeter wavelengths radio emission from

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Figure IX, 1. VLT image of the nearest radio galaxy Centaurus A. On the scale of this image, the radio emission (synchrotron radiation) extends over more than 10 meters, demonstrating the presence of magnetic fields and cosmic-ray electrons more than a million light years from the galaxy.

warm (10 000°) ionized interstellar matter is also observed. In addition, the spin flip line of atomic hydrogen at 21-cm gives very detailed information about the diffuse interstellar gas. Since this line has a fixed intrinsic wavelength, velocities of the gas can be measured from the Doppler effect. Much of the information about the motion in galaxies is obtained in this way from which inferences about the presence of “dark matter” have resulted. However, at large distances the angular diameters of the galaxies become very small

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and a high angular resolution is required. The same is the case for the study of remote quasars and radio galaxies in which the jet-like structures made of relativistic particles give information on the energetic processes taking place there and on the surrounding intergalactic medium. While the 21-cm line is a rather isolated feature in the radio spectrum, at mm wavelengths a plethora of emission lines appears due to molecules in the cool (10–1000 K) interstellar gas. In addition to lines of common molecules like CO at 3 mm and at shorter wavelengths, very complex molecules have been found in dense molecular clouds. As a result, cosmic chemistry has become an active branch of the astronomical sciences. Intricate chemical reactions take place on the surfaces of interstellar dust grains and in the atmospheres of cool supergiant stars. The resulting large molecules may play an important role in the formation of planets. Some scientists also believe that their presence on early earth may have been a factor in the origin of life. At very long wavelengths simple antennas made of some wires have been used, but most radio telescopes at decimeter to millimeter wavelengths follow the same model as optical telescopes – Cassegrain or prime focus. However, there are two important differences. The angular resolution given by θ § 200 000 λ / d arcsec with λ the wavelength and d the diameter of the telescope, is evidently much poorer at radio wavelengths. Thus, at 10 cm even a 100-m telescope has a resolution no better than 200 arcsec, inadequate for most purposes. So except at mm wavelenghts radio astronomy is done mainly with interferometers. The other point is that in order to have a good image quality and sensitivity, the collecting surface of the telescope should reproduce the theoretical form (usually a paraboloid) with an accuracy of the order of λ/20. Thus, at 10 cm deviations from the perfect shape of as much as 5 mm are entirely acceptable. So a radio telescope is very much cheaper than an optical one of the same diameter; fully steerable 100-m telescopes have been built. Of course at (sub)mm wavelengths radio telescopes also become more costly. The only way to obtain subarcsec resolution in the radio domain is to build an interferometer. While in practice the interferometric combination of optical telescopes has been a rather difficult undertaking, the long wavelengths in the radio spectrum greatly simplify this. Various techniques exist to amplify signals and to combine them coherently. Arrays of tens of telescopes have been built, scattered over areas tens of km in diameter. In the expression for the angular resolution d is now the separation of the most distant telescopes. The signals coming from the different telescopes may be transported through wires, radio links or fiber optics cables to a common place where the correlation takes place. In fact, it is not even necessary to connect the telescopes in these ways, one can also register the signals of each telescope on tape and then a posteriori combine the contents of the tapes in a computer. To be able

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to do this, a sufficiently accurate (atomic) clock at each site is needed to synchronize the tapes. This is the principle underlying the VLBI (Very Long Baseline Interferometry) which has made it possible to combine the signals of telescopes on different continents. Thus, in the expression for the angular resolution d is now of the order of the diameter of the earth. With d = 10 000 km at a wavelength of 1 cm a resolution of 0.0002 arcsec (0.2 mas) may be reached. Still larger baselines with d = 20 000 km have been obtained by correlating the signals of the space based 8-m radio telescope HALCA of the Japanese Space Agency with those from ground based arrays.

Large single telescopes Two large fully steerable radio telescopes were built in Europe early in the development of radio astronomy: a 76-m at Jodrell Bank near Manchester in 1957 (Figure I, 2), and a 100-m at Effelsberg in Germany in 1972 (Figure IX, 2). Both have been subsequently upgraded, and at present the 76-m is usable at 3 cm wavelength and the 100-m at 3 mm, albeit with reduced effective area. A 64-m telescope, also functional at 3 mm, is currently under construction in Sardegna. While these national telescopes have their separate scientific programs, they are particularly useful in the context of the EVN, the European VLBI Network. Two other large telescopes exist in the

Figure IX, 2. The 100-m Effelsberg telescope of the MPG; the solid central part is now usable to 3 mm wavelength.

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world: the 64-m Parkes (Australia) telescope built in 1961 and a 100-m completed in 2002 in West Virginia. Several less flexible large telescopes have also been built of which the 305-m Arecibo (Puerto Rico) has been the most successful. It has been constructed in an appropriately shaped mountain valley. So the spherical primary mirror is immobile, but by moving the instrument cabin at the prime focus a rather large area of the sky may be accessed. In Europe, at Medicina near Bologna a cross antenna (Figure IX, 3) was built in 1964 with, in its final form, NS and EW arms about 600 m long, yielding an angular resolution of some 4 arcminutes at a wavelength of 75 cm. The total collecting area is 30 000 m2, some 40% of that of the Arecibo dish. A 200 × 35 m transit instrument at Nançay (near Orléans), also with a fixed mirror, has recently been upgraded. For most purposes interferometric telescope arrays have now taken over if superior angular resolution and shorter wavelengths are desired.

Figure IX, 3. The “Croce del Nord” at Medicina near Bologna. With 600 m long arms it combines good angular resolution and sensitivity at 75 cm wavelength. Installation of fiber optics could allow a greater bandwidth and, thus, a higher sensitivity. To the right is the more recent 32-m telescope which is used for VLBI observations.

Interferometric Arrays Two-telescope interferometers have been constructed in various places to improve angular resolution. At Cambridge (UK) much of the technology was developed and early results on the structure of radio galaxies obtained. In particular the synthesis methods were pioneered, in which the rotation of

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the earth changes the orientation of the line connecting the telescopes with respect to the source, so as to obtain resolution in two dimensions. A large linear array along these lines was constructed in 1970 in Westerbork (NL) which today consists of 14 telescopes of 25-m each. A decade later it was superseded by the Very Large Array in New Mexico. The VLA consists of 27 mobile telescopes of 25-m distributed in Y shape with longest baselines between telescopes of 36 km (Figure IX, 4). The advantage of the Y shape is that one has immediately two-dimensional image information over the whole sky. The earth rotation based synthesis methods are not usable close to the celestial equator. The radio astronomy community is much more apt to share facilities than the optical, where telescope access tends to be more strictly proportional to the investment made. As a consequence, European astronomers have frequently observed with the VLA as US astronomers had done at Westerbork. A major 60 M$ upgrade is planned with the addition of several telescopes, increased sensitivity and angular resolution, and wavelength coverage down to 3 mm3). In the meantime, operations also began in 1980 at the Multi-Element Radio Linked Interferometer in the UK. MERLIN is now composed of six 25 m class telescopes (including one recently added of 32 m) and the 76-m

Figure IX, 4. The VLA in New Mexico. With 27 mobile 25-m telescopes distributed in Y shape 36 km across, it combines high sensitivity and excellent angular resolution. The future SKA could be 30 times larger and with an 80 times larger collecting area. Frequently European scientists have obtained valuable data with the VLA.

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at Jodrell Bank. Baselines range up to 217 km. An upgrade (e-MERLIN) will see the radio links replaced by fiber optics cables. This allows the receiver band width to be augmented and, thus, the sensitivity increased by up to a factor of 30. Expansion of MERLIN with an Irish telescope has been discussed. In the southern hemisphere there is the Australia Telescope, composed of 6 telescopes of 22-m, which was recently upgraded to operate at 3 mm wavelength. As the dominant radio astronomical facility in the southern hemisphere, the AT also plays an important role in collaborative programs with the ESO telescopes in Chile. For longer wavelengths India has built an array of thirty 45-m telescopes usable above 20 cm. It has an unprecedented sensitivity and angular resolution above a wavelength of 50 cm. Japan has constructed an array of a 45 m and six 10-m telescopes for observations at wavelengths of several millimeters. It may be usable down to 1 mm, though the humidity of the Nobeyama site is an obstacle.

VLBI Very Long Baseline Interferometry has frequently been performed on an ad hoc basis between radio telescopes in various parts of the world. By now, however, VLBI has become more organized and an important part takes place in organized networks. In the US a dedicated VLBI network was built, the Very Long Baseline Array (VLBA) composed of ten 25-m telescopes at sites ranging from Puerto Rico to Hawaii – a distance of about 8000 km. Operations down to 3 mm should be possible, corresponding to a resolution of some 0.08 milliarcsec. The first VLBI observations in Europe were made in 1976 with radio telescopes at Onsala (S), Dwingeloo (NL) and Effelsberg (D) participating. A more formal cooperation, the European VLBI Network (EVN) was set up four years later. The need for a more institutional framework to construct a large 16-telescope correlator and to more properly organize the operations led in 1993 to the creation of the Joint Institute for VLBI in Europe (JIVE) in Dwingeloo. An initial investment of some 7 M€ was contributed mainly by the Dutch, while the EU also made a small contribution. Most of the radio telescopes in the EVN (Table IX, 1) had been in existence before the VLBI network was organized and, as a consequence, the location of the telescopes was perhaps somewhat less optimized than in the VLBA. However, with some new telescopes added, this is no longer a problem. In fact, the availability of north–south baselines in addition to those oriented east–west greatly improves the image quality, while several very large telescopes in the EVN lead to a high sensitivity. European baselines being limited, it was important to extend the EVN into Asia. The inclusion of two telescopes in China now yields baselines of up to 9000 km. In the meantime, the telescopes at Arecibo and at Hartebeestpoort (South Africa) have also become associated with the

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Table IX, 1. The European VLBI Network (EVN).

Location Jodrell Bank (UK) Five telescopes in UK Cambridge (UK) Westerbork (NL) Effelsberg (D) Wettzel (D) Yebes (ESP) Onsala (S) Metsähovi (SF) Torun (PL) Medicina (I) Noto (I) Sardegna (I) Seshan (PRC) Nanshan (PRC)

Diameter (m)

min. λ (mm)

76* ~ 25* 32* 94+ 100 20 14 40 20 25 14 32 32 32 64++ 25 25

30 13 7 30 3 30 3 3 3 60 3 7 7 7 3 13 13

* These telescopes form the MERLIN (Multi Element Radio Linked Interferometer) array. An upgrade to fiber optics links is in progress. + Actually a 14 × 25 m tied array. ++ Completion in 2007.

EVN (Figure IX, 5) further increasing the baselines. The the EVN is that most telescopes are also used for other total time available has been no more than 1000 hours this time was used for joint operation with the VLBA or satellite HALCA3) with its 8-m telescope.

main drawback in programs and the per year. Some of with the Japanese

Space VLBI The size of the earth limits the resolution that may be obtained with ground based VLBI arrays. So it was only natural that suggestions were made to incorporate in the global arrays some space based element. Several proposals were made to ESA from 1979 onwards, but these have not been selected in the competition with other missions. This may have been due to a feeling that this was niche science which would allow improved resolution on a relatively small number of sources and also to the relatively weak radio community in the overall space research setup. However, the case for the

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Figure IX, 5. The sites of the EVN, the European VLBI network.

science remains compelling. We still have only limited understanding of the radiation mechanisms that allow extreme brightness temperatures to be reached in quasars and other sources. In Russia the 10-m RADIOASTRON project seemed promising, but funding difficulties have delayed its realization (till 2007?). The only successful mission to-date has been the HALCA satellite within the Japanese VLBI Space Observatory Program (VSOP). The satellite carries an 8-m radio telescope, operating at 1.6 and 5 GHz (20 and 6 cm). The orbit has an apogee of 21000 km, yielding a maximum resolution of 0.3 milliarcsec. The cooperation with the ground based arrays has been very successful and demonstrated the validity of the concept. An improved version is being planned. VSOP-2 will have a 12-m telescope. In the US there is a project for a 25-m orbital telescope, usable till 86 GHz, which could be realized later in the decade.

(Sub)Millimeter telescopes As noted before, telescopes should have a collecting surface with shape errors less than 1/20 of the wavelength or at 1 mm errors of less than 50 μm. Considerable care is needed to achieve such a precision for telescopes operating in the open air. The Sun, wind and temperature variations in addition to deformations due to gravity may create problems. Moreover, the atmosphere becomes less transparent at short wavelengths with water vapor being the main culprit. So it is important to place mm/submm telescopes on high dry sites. This is even more critical for interferometers where variations

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in the water vapor above different telescopes may be fatal. In Table IX, 2 are listed the large telescopes that can function effectively at or below 1 mm. It is seen that Europe has been doing rather well in this domain. In the early seventies both French and German astronomers were considering possible ventures in (sub)mm astronomy. While the latter wanted to build the largest possible reflector for maximum sensitivity, the former felt that the angular resolution would be inadequate and opted for an interferometer. Both projects suffered from difficulties in obtaining sufficient technical personnel within their organizations, while at the time funding was less of a problem. The solution was found by founding a new entity, l’Institut Radio Astronomie Millimétrique, on a fifty-fifty basis between the MPG and INSU which would operate a single dish of 30-m diameter at the Pico Veleta (2900 m) near Granada in Andalusia and an interferometer of 15-m telescopes on the Plateau de Bure near Grenoble in the French Alps. Headquarters would be in Grenoble. In the meantime, the number of 15-m telescopes has grown to six and Spain has joined IRAM. The Pico Veleta location was financially favorable, because a nearby skiing area provided relatively easy access. The Plateau de Bure at 2500 m was more difficult, and a special cable cart had to be constructed to transport people and equipment. In 2001 a terrible tragedy happened when a cable broke. Soon afterwards, when transport was assured by helicopter, a crash caused further disaster. Table IX, 2. Radio Telescopes with min λ ” 1 mm.

location/Name

Diameter

Organization/ Countries

2900 m 2500 m 4000 m 2400 m 5000 m 3200 m

Pico Veleta (ESP) Plateau de Bure Hawaii/JCMT La Silla/SEST* Chajnantor/APEX Mt. Graham, Arizona/H. Hertz

30-m 6 × 15-m 15-m 15-m 12-m 10-m

IRAM IRAM UK/NL/Can S/ESO D (MPG)/S/ESO D (MPG)†/Arizona

4600 m 2100 m 4000 m 2600 m++ 2600 m++ 4000 m

Sierra La Negra, Mex/LMT+ Kitt Peak, Arizona Hawaii/Caltech California/Caltech California/BIMA Hawaii/SAO

50-m 12-m 10-m 6 × 10-m 9 × 6-m 8 × 6-m

Mex/US US US US US US/Taiwan

Altitude

* Operations discontinued in 2003. † Participation terminated. + Not yet completed. ++ In 2004, was lower before being moved. The two arrays are now combined into the CARMA array.

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A total of 24 people perished in the two accidents. Following a difficult period, the interferometrer has resumed full operations. Important results have been obtained with the two facilities. The 30-m, completed in 1985, has remained the world’s largest submm telescope for nearly two decades. It has mapped molecular clouds, detected new lines from molecules and found very faint sources associated with quasars. More recently with the MAMBO2 117 element detector surveys for sources have been made at 1.2 mm. The interferometer with baselines of up to 300 m (Figure IX, 6) has yielded angular resolutions of better than an arcsec at 1 mm. As a result, it was able to begin to resolve stellar envelopes, star and planet forming regions and some gas rich galaxies at large redshifts. Importantly it found that substantially higher resolutions would be needed to analyze such objects properly and so pointed the way towards ALMA. Both at IRAM and at the other European mm telescopes much engineering work was done on improving submm and mm receivers for increased sensitivity. While IRAM has been a great success, climate at the European sites has limited submm observations and especially the access to the important 0.3 mm window. The same has been the case for the 10-m Heinrich Hertz

Figure IX, 6. The IRAM interferometer on the Plateau de Bure near Grenoble. With the six 15-m telescopes angular resolutions better than 1 arcsec have been attained at 1 mm wavelength.

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telescope at 3200 m altitude on Mt. Graham in Arizona. It was built by the Max-Planck-Institut für Radioastronomie and operated conjointly with the University of Arizona. During summer conditions are very poor. In the meantime, the MPIfR has abandoned the telescope in favor of APEX. Undoubtedly the best location so far is the area near the top of Mauna Kea, Hawaii, at 4100 m, where the UK in cooperation with the Dutch and the Canadians has placed the 15-m JCMT (James Clark Maxwell Telescope). With the SCUBA detector array at 0.85 mm highly interesting observations have been made of sources associated with obscured galaxies with stunningly high rates of star formation4). These have again shown the promise of larger telescope arrays at still better sites.

SEST and APEX In the early eighties large submm telescopes were still lacking in the southern hemisphere. But it is here that the most interesting objects for investigations at mm wavelengths are situated: the center of our Galaxy and the areas around it with dense molecular clouds, the Magellanic Clouds with interesting areas of star formation, and Centaurus A (Figure IX, 1) the nearest radio galaxy which also contains much molecular gas. Occasionally the ESO 3.6 m telescope was used to study CO at 3 mm wavelength. However, the telescope was far from optimal for this and also lacked the necessary angular resolution. Moreover, it was a bit of a waste to use its excellent optical surface for observations at long wavelengths where a rougher surface would suffice. Nevertheless, these early observations indicated what a more suitable telescope would be able to do. At Onsala, near Göteborg (S), much expertise in radio receivers for mm wavelengths had been built up in conjunction with two 20-m class telescopes there. So it was natural for its newly appointed director, Roy Booth, in 1984 to initiate steps to build a southern submm telescope. Since IRAM had started the construction of its six 15-m telescopes, it seemed most effective to construct an extra one appropriately modified for a fixed pedestal, an idea enthusiastically embraced by its director, Peter de Jonge, who previously had headed the telescope operations and technical services at La Silla. At La Silla there was ample space to place the telescope. Since the Swedes had only half the necessary funds and since others in the ESO member countries were interested, the project finally became the Swedish ESO Submillimeter Telescope (SEST). Initially there was some concern in the Council about ESO going into radio astronomy. But after I had pointed out that radio waves below 1 mm could be considered part of the IR, there were no further problems. The SEST project came at a favorable moment. Italy and Switzerland had just joined, and so some new funds were available. While the VLT was looming in the future, it was too early to use these funds for it, and Council

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was unwilling to take any action that might imply a commitment. On the other hand, it is dangerous to have too much uncommitted money lying around, and so SEST fitted in very well. With the unique scientific opportunity of the first large submm telescope in the southern hemisphere being recognized, approval came easily and SEST was installed at La Silla late in 1987 at a total cost of 9 M€ (in 2004 €). Prior to the installation it seemed desirable to measure the wind speed during the winter months at the selected site, so as to be sure that the specifications for survival were sufficient. A high mast with an anemometer was placed there. During one of the storms it was destroyed after having registered 186 km/hour, and we shall never know the maximum wind speed. Since the nominal limit of 200 km/hour for the telescope contained some extra safety factors, and since insufficient time was left for further measurements, we decided to take the risk that higher speeds would occur. A more serious disaster occurred during the assembly of the telescope. The reflector was pointing to the zenith; it had high reflectivity also in the visible. Since at midsummer the Sun passes at only 6° from the zenith, enough energy was concentrated on the secondary to start a fire. The La Silla fire brigade energetically extinguished the fire, which caused burning pieces to fall on the primary. A fair amount of damage resulted as well as some delays in the completion. Following this, however, no further mishaps occurred, and during the next 16 years the telescope functioned well. Among the noteworthy results of SEST were the following5): the discovery of the coldest gas in the Universe in the Boomerang Nebula where CO is seen in absorption against the 3 K microwave background. Such gas can only be cooled to such a low temperature because it is expanding rapidly; the discovery of some 600 mainly molecular lines, many of which remain unidentified in the absence of adequate laboratory data; the discovery of dense gas in a so-called Bok globule, opaque to visible radiation, in which curiously no stars are being formed as might have been expected because of the high density; studies of detached circumstellar envelopes, very thin structures of short lifetime (< 10,000 years) which are expelled by evolved low mass stars during periods of explosive helium burning; observations of molecules in comets, including among others CO, OH, H2S and HCN. In addition, large scale maps of CO in the Magellanic Clouds and in the Galaxy were obtained. Some of these maps should be very valuable to find interesting regions for further study by ALMA. CO is important because it provides a tracer for molecular hydrogen, which itself is much harder to observe because of its unfavorable molecular properties, but which accounts for most of the mass of dense interstellar matter. SEST also has been used for experimental VLBI in the mm domain. La Silla is a good site for mm observations but still has too much atmospheric water vapor to be an optimal submm site. With the development of the 5000 m high Chajnantor site for ALMA a far better opportunity arose (Figure IX, 7). Since the surface of SEST is not very suitable for the shorter

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frequency 400

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Figure IX, 7. The transparency of the atmosphere at submm wavelengths. The blue areas represent wavelengths at which the transparency is better than 50% or in the lowest strip 10%. The amount of precipitable water corresponds to 1 mm equivalent in the upper strip and 0.5 mm in the other two. At La Silla 1 mm H2O would be highly exceptional. At Chajnantor values in the 0.5–1.0 mm range prevail some 50% of the time.

submm wavelengths and since the cost of moving it would be quite high, a new 12-m submm telescope has been erected at Chajnantor, where in some years’ time the 64 telescopes of ALMA will be placed. This Atacama Pathfinder EXperiment, APEX (Figure IX, 8)6), will also serve as a test of the conditions and operational problems at this rather difficult site. APEX is a collaboration of the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn (50%) with the two SEST partners, ESO (27%) and Onsala (23%). Because it was difficult to finance both telescopes, normal operations at SEST have been terminated mid-2003. APEX should become operational in 2005, initially with the 1.3 mm receiver from SEST and soon thereafter with others. It is planned to equip APEX with receivers covering the atmospheric windows from 1.5 mm to 0.3 mm and to test the possibility for observation at even shorter wavelength. Of course, the angular resolution is far inferior to that of ALMA, but at 0.3 mm it is still 5 arcseconds. With its relatively large field of view it is well suited for mapping projects to search for early star forming galaxies and protostars in our Galaxy in addition to spectroscopy of many molecular lines important in astrochemistry. APEX will be operated by a staff of 18, largely by remote control from a base constructed by ESO at about 2500 m altitude in the village of San Pedro de Atacama.

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Figure IX, 8. APEX, the 12-m Atacama Pathfinder Experiment, a cooperative venture of the MPIfR, Sweden and ESO. In the very dry atmosphere of Chajnantor it should be fully functional down to 0.3 mm and perhaps obtain useful results at even lower wavelengths.

ALMA The IRAM interferometer data have shown that many structures observable at submm wavelengths are quite small in angular measure. Examples include the disks around stars where planets are forming or dense regions in the interstellar or circumstellar gas where conditions for chemical reactions are favorable, as well as the structures in galaxies far out in the Universe. To adequately study these a resolution better than 0.1 arcsec is needed which requires interferometers with baselines of several kilometers. But the radiation is feeble, and in objects resolved by such an interferometer the amount of flux in one beam area is small. Hence, a large collecting area is needed to be able to profit from the high angular resolution. In fact, in many cases an angular resolution of 0.1 arcsec is only useful if the total collecting area is of the order of 10,000 m2. The first ideas about a European Large Southern millimeter Array (LSA) arose in discussions among radio astronomers around 1991. The IRAM interferometer on the Plateau de Bure had shown the power of mm interferometry, and it was time to reflect on the next step. Early on it appeared that a southern site was preferred because of the greater richness of the southern

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Galaxy and because particularly suitable dry sites exist in the Chilean Andes. Moreover, a southern site would be optimal if the results of observations at radio and optical wavelengths were to be combined, the latter to be obtained with the VLT. ESO had already become involved in the SEST project, so it became an early partner in the LSA discussions. Some initial studies were made by IRAM, ESO, the Onsala Space Observatory in Sweden and the Netherlands Foundation for Research in Astronomy, and a document outlining the project7) was presented in late 1995 to a workshop held at ESO8). The LSA was to be a mm array optimized for maximum sensitivity at 3 mm and 1.3 mm wavelengths, but ultimately covering the atmospheric windows from 7–0.8 mm. The total collecting area was to be 10,000 m2 to ensure the required sensitivity at a resolution of 0.1 arcsec. A dry site above 3000 m was being looked for. This still left the diameter of the individual telescopes to be decided. If the telescopes are very small, their number becomes very large. But each telescope has fixed costs independent of its diameter: receivers, links to the central area and infrastructure. Also the problems associated with the correlation of the outputs of the telescopes rapidly increase with their number. On the other hand, if the telescopes are large, their field of view becomes small, and so does the area that may be mapped by the interferometer. Moreover, problems with wind forces and other environmental problems are aggravated. The conclusion was that the optimal array would consist of 50 × 16-m telescopes or possibly 100 × 11-m. The cost of the LSA was estimated at some 270 M€ . Also in the US a project was being developed, the MMA (MilliMeter Array). It would have a smaller collecting area of 2000 m2 and be composed of 40 × 8-m telescopes operating down to 0.3 mm. The emphasis on (sub)mm science led to the relatively small unit telescopes. With larger telescopes the field of view was thought to be too small at the very low wavelengths. It also required a very high, dry site. The Llano de Chajnantor at 5100 m was being investigated as a possibility. Even though the MMA and the LSA had somewhat different objectives, the idea of having two large arrays in northern Chile with substantial costs for infrastructure seemed wasteful. So it was finally decided to merge the two projects into ALMA – the Atacama Large Millimeter Array. ALMA9) would be a joint project on a fifty-fifty basis between the US+Canada on the one hand and Europe on the other. After some clumsy initial arrangements in Europe, the situation was simplified when the UK joined ESO. Thus, ESO now represents Europe in the ALMA cooperation, with Spain having concluded a separate agreement with ESO of which it is not yet a member, though negotiations about a possible membership have taken place from time to time. ALMA should consist of 64 telescopes of 12-m diameter for a total collecting area of 7240 m2 (Figure IX, 9). It will cover the atmospheric windows from 0.3–10 mm wavelength. The initial set of receivers should cover the wavelength ranges 3.6–2.5, 1.4–0.81 and 0.50–0.42 mm. Additional

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Figure IX, 9. ALMA. With 64 telescopes of 12-m diameter an excellent sensitivity is achievable. The longest baselines of 14 km will provide an angular resolution better than 0.02 arcsec at 1 mm wavelength.

receivers could be implemented later, but of course every time 64 copies are needed which makes this rather costly. It is one of the advantages of APEX that receivers can be installed singly so that the returns can be evaluated before a major commitment has to be made. Placed on the Llano de Chajnantor (Figure VI, 8), ALMA will have maximum baselines of up to 14 km, corresponding to angular resolutions of 0.004–0.15 arcsec according to wavelength. The telescopes of the array can be moved on big trucks, so as to have either a compact array with very high sensitivity to resolved objects or an extended array for maximum resolution. Also in Japan there were plans for a large mm array of 50 × 10-m telescopes. A site close to the Llano de Chajnantor was under study. Unfortunately, financial problems initially prevented Japan from joining the ALMA cooperation, but these have now been solved. Additional telescopes will be integrated into the array, making it even more powerful. Construction of ALMA has now been started. The full array should be completed by the end of 2011, but some observations with part of the

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array could perhaps begin as early as 2007. The agreed cost envelope for Europe and N. America is 552 MUS$ (year 2000). So the cost to Europe is some 250 M€ (2004) of which ESO will pay 92.5% and Spain 7.5%. The project has one director serving under a board composed of equal numbers of N. American and European representatives. Of course, Chile as the host country is also very much involved in the project, providing the site and other facilities. In projects of this magnitude, issues of industrial return play an important role. The construction of the individual telescopes is a substantial item in the overall budget. As a first step, industrial companies from both sides of the Atlantic have been invited to manufacture a prototype. The resulting two prototypes have been shipped to the VLA site in New Mexico for comparative tests. Depending upon the results, one will have to proceed cautiously to equilibrate the total contributions from both sides. Perhaps more worrisome, the financial envelope was set on the basis of estimates of the telescope costs before prototypes were constructed. If the final unit costs were to exceed these estimates, there would be little choice but to reduce the number of telescopes. The alternative of increasing the financial envelope seems very difficult on both sides of the partnership. So it is fortunate that Japan is bringing in additional telescopes. Undoubtedly, with this first 50-50 trans-Atlantic large scientific project disagreements will occur. Success in dealing with these will very much influence future cooperations of this kind. However, the presently foreseen administrative arrangements are not entirely promising. Possibly the full Japanese integration in ALMA, making it a truly tripartite venture, could in some ways simplify matters. As mentioned before, MPIfR, ESO and Onsala are placing a first, somewhat modified, ALMA type 12-m telescope at Chajnantor, so as to gain a number of years of submm observing before ALMA comes on line. The Atacama Pathfinder EXperiment, APEX, will also serve as a valuable test of operating a telescope at such high altitude. With APEX and ALMA the European community will have access to the most advanced submm facilities in the world. Also Japan is placing a 10-m submm telescope, ASTE, nearby at 4800 m on the Pampa La Bola10). ALMA should have a broad impact on many domains of astrophysics. Its exquisite angular resolution will allow the study of star and planet formation in detail. In its wavelength range numerous lines of sometimes quite complex molecules are found and the astrochemistry of their formation can be studied. The circumstellar envelopes where dust and molecules form are also a prime target. Interesting data on molecules in comets and planetary atmospheres may be expected. The dust emission from very early galaxies should be measurable with ALMA as will be molecular gas in galaxies and quasars at a wide range of redshifts. Many other topics could be enumerated.

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SKA – The Square Kilometer Array ALMA will have subarcsec angular resolution at mm wavelengths. To have the same resolution at decimeter wavelengths, an array would have to be spread out over an area 1000 km across. It is, of course, true that the VLBI networks achieve even better resolutions, but because their telescopes are so sparsely distributed, the image quality is rather limited and the sensitivity frequently inadequate. The collecting areas of the VLBI networks and their prospective enhancements amount to less than 50,000 m2. Taking into account a dose of financial realism, radio astronomers around the world have set an aim to have a million m2 – hence the Square Kilometer Array. At the IAU meeting in Sydney in July 2003 a memorandum of understanding was signed by scientists from Australia, Canada, China, D, India, I, NL, PL, S, UK and the US to collaborate on the design, search for funding and construction of SKA. It would have been very simple if the results of the decimeter observations could also be obtained at mm wavelength, where ALMA has the necessary resolution. However, in the mm range one observes the cool gas in the galaxies, while at decimeter wavelengths hot gas and synchrotron radiation from cosmic-ray electrons predominate. Moreover, at large redshifts important lines, like the CO line at 2.6 μm, are beyond the range of ALMA, which in any case at longer wavelengths would have inadequate angular resolution. In addition, at 21-cm the ubiquitous spin flip line of hydrogen is observed which usually comes from regions so tenuous that few molecules are present. So ALMA and SKA address entirely different areas of science. The specifications of SKA11) are simple: 1 km2 collecting area, baselines up to 3000 km or more, a flat, quiet site with low artificial radio noise and as large a field of view as possible. A Y-shaped layout, like the VLA, or perhaps a spiral-like arrangement is envisaged, but the telescopes will not be mobile. Observations should be feasible at wavelengths from at least 3 m to around 1 cm, with an imaging field of view of a square degree at 21-cm. With these specifications the wavelength coverage of SKA + ALMA extends continuously from 3 m to the atmospheric limit around 0.3 mm, with an angular resolution everywhere better than 0.2 arcsec and with a field of view that gradually narrows from square degrees to 30 arcsec2 at the shortest wavelengths. Suitable locations for SKA exist in Western Australia; other sites may be found in China, South Africa and Argentina. With ALMA in the southern hermisphere, it would be important to have SKA also there so that the complementarity of the two may be fully utilized. A typical 100-m telescope usable to 1 cm should cost at least 25 M€. If the SKA were to be made up out of 127 such telescopes, the total cost would amount to some 3000 M€ for the telescopes alone. The replication savings of manufacturing many telescopes at the same time would substantially

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reduce this sum, but when all the other items are added it probably would be difficult to bring the total cost far below the 1000 M€ mark. However, entirely different technologies involving phased arrays may be used. Here very cheap detector elements view a large area of the sky at once. Extensive computer processing then picks out from all the signals, those coming from a particular area in the sky. While this would be a very attractive option, the computer requirements are enormous. So for now it is difficult to estimate what the total cost will be. Other proposals for SKA involve an array of Arecibo-like fixed dishes for which a certain area of China would be promising. But in whatever way SKA is finally constructed, it is likely to have a cost in the 500–1000 M€ range. The scientific potential of SKA11) is enormous. As an example, consider the “epoch of reionization” when the neutral gas in the Universe began to be ionized by the uv radiation from the first stars and quasars in the newly forming galaxies. The 21-cm line of hydrogen observed at redshifts of 7–15 (i.e. at wavelengths of 1.7–3.4 m) would give much information about conditions in the Universe at that crucial time during which the outline of the present day world became visible for the first time. Also the 2.6 mm line of CO molecules could be observed with SKA at redshifts above 3–4. So it should be possible to detect the very beginning of the formation of elements like C and O. We also note here the complementarity of ALMA and SKA. With ALMA higher order lines of warm CO and other lines at smaller wavelengths may be observed at high redshifts as well as the dust continuum emitted by typical star forming galaxies. Again, SKA can study the 21-cm emission in galaxies at lower redshifts and ALMA their CO emission. A complete view of the evolution of the gaseous component of galaxies at modest redshifts could be obtained. Magnetic fields have been detected (from the Faraday effect, the rotation of the plane of polarization in an ionized magnetic medium) in many galaxies and also in clusters of galaxies. Nothing is known about their evolution, their first origin or the cosmological effects they may have produced. A very complete inventory of pulsars, radio sources pulsing with periods of 0.001–10 seconds, in our Galaxy could be obtained. Typical pulsars are rotating magnetic neutron stars that emit narrow beams of electromagnetic radiation. Several pulsars are known in binaries, orbiting another neutron star. Rare cases are expected to be discovered of pulsars orbiting black holes which would give much information on the properties of spacetime around these. Of course, there is much more to SKA than these items: quasars and galaxies with bursts of star formation at high redshifts, stellar atmospheres and circumstellar flows, supernovae and gamma-ray bursts, exoplanets and many others. The Dutch project LOFAR12) (LOw Frequency ARray) will make use of the phased array technology. LOFAR would observe the long wavelength part

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of the radio spectrum in the range 30–1.4 m, that is at frequencies of 10–220 MHz. While the technology is simpler at longer wavelengths, the ionosphere creates serious problems. LOFAR could be constructed on a five year time scale at an estimated cost of the order of 150 M€. Extensive technology development is needed which also has commercial implications. With the antenna elements distributed over a 300 km diameter area, the angular resolution at 30 m would be some 20 arcsec, and around 1 arcsec at 1.5 m. Because of the long wavelengths and of the ionospheric problems, progress in this wavelength domain has been slow until now. LOFAR should open up the field. LOFAR would be completed long before SKA. Some of the scientific aims are not very different from those SKA has set and may later achieve with superior resolution and sensitivity. However, most of the 3–30 m wavelength domain will not be accessible to SKA. Unique results could be obtained on sources of coherent radio emission, pulsars, quasars with very steep spectra, exoplanets with Jupiter-like radio emission, as well as in ionospheric studies, observations of coronal mass ejections from the Sun with the resulting “space weather” and the detection of radio waves from the air showers of extreme cosmic ray events. The history13) of LOFAR shows some of the pitfalls of international collaborations in which the siting plays an essential role. In the early nineties it was discussed as a relatively cheap NL–US project with possibly also Australian participation. With costs escalating and disagreements about the site and about the scientific optimization, the collaboration fell apart. Now there are four projects: The LOFAR of the Dutch, with German participation, is still by far the largest. A US project, the Long Wavelength Array, will be placed in the SW US, a US–Australia project – the Mileura Telescope in W. Australia, and a Canada–China–US project, the Primeval Structure Telescope in China. Different US groups participate in the different projects. Part of the problem has been that funding available on one site was not transferable to another. Similar problems could be faced by SKA. Note added in proof: Because of the increased prices of steel and carbon fiber, the cost of the ALMA telescopes came in higher than expected. As a consequence, the number of 12-m telescopes has been reduced from 64 to 50.

X. Europe in Space: ESA’s Horizons 2000

Le risque de surdépendance vis-à-vis des États-Unis ne doit cependant pas être ignoré, et il convient de faire en sorte que la part de notre activité scientifique qui dépend de décisions américaines, prises à partir de considérations qui ne sont pas nécessairement les nôtres, ne devienne pas prépondérante… Dépendance. Indépendance. Interdépendance et surdépendance. Voilà un beau sujet de dissertation et pas seulement dans l’espace. H. Curien1)

Following a schedule very similar to that of ESO, European space science came into being in Paris on 14 June 1962 with the signing of the convention for the European Space Research Organization (ESRO). It took effect on 20 March 1964 upon ratification by nine countries (A, B, DK, F, D, NL, S, CH and UK), soon joined by Italy. A month earlier the European Launcher Development Organization (ELDO) had been founded, which turned out to be a preprogrammed failure: different countries were responsible for different parts of a rocket, and not surprisingly the interface problems could not be properly handled. As a minister remarked after one of the launches of its “Europa” rocket, it seemed that the organization was involved in deep sea research! ESRO was more successful; by 1980 a dozen relatively small satellites had been placed in orbit, albeit with American rockets. Most of ESRO’s satellites were for studies of the earth’s magnetosphere, aurorae, the ionosphere and the nearby interplanetary medium, but three were concerned with science outside the solar system: TD-1 (1972–74) obtained data on stars in the ultraviolet, COS B (1975–82) very successfully mapped the sky in gamma-rays, and IUE (1978–96) – the International

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Ultraviolet Explorer – carried a small (45 cm) telescope equipped with a spectrograph; IUE was a cooperation of ESA, the UK and the US. More than any other mission it succeeded in integrating space data into mainstream astronomy. In total, some 3000 articles in refereed journals have been based on the 110,000 spectra obtained by IUE. Till the end it remained in heavy demand by a broad astronomical community. The aging spacecraft was deliberately turned off in 1996 because its cost-to-benefit ratio diminished, while the participating agencies had financial problems. After these successful beginnings ESRO began planning for larger missions which soon exceeded its financial and technological means. With ELDO a failure and ESRO’s future uncertain, a fundamental reorganization was needed. In 1975 the convention creating the European Space Agency (ESA) was signed by the ESRO member states, minus Austria, but including Spain. In 1987 Austria, Ireland and Norway became full members, followed by Finland in 1995, Portugal in 2001, and Greece and Luxembourg in 2004. ESA would be responsible for research, launchers, space technology and its applications. Its headquarters were placed in Paris, the European Space Technology Centre (ESTEC) in Noordwijk (NL), the European Space Operations Centre (ESOC) in Darmstadt (D) and the European Space Research Institute (ESRIN) in Frascati near Rome. The function of the latter was variable and not always clear, except that politically it had to be continued in Italy. In the meantime also a center for managing astronomical missions has come about in Villafranca near Madrid. This was started for dealing with the European part of the International Ultraviolet Explorer and continued with ISO and XMM-Newton. When the gamma-ray mission INTEGRAL came along, ESA very rationally put the data center as an “instrument” and, in fact, the Swiss were successful in obtaining this, with a greatly reduced cost to ESA. This sent alarm bells going off in Madrid, with the result that ESA decided to place the data centers for all future astronomy missions in Villafranca. An outside observer might wonder why pay for something one could have got partly for free, but this is not the way Europe functions. The development of an independent European launcher capability was an essential part of the agreements, with Kourou in French Guyana as the launch site. Space Science was a relatively small part of ESA, representing of the order of 10% of the total budget. While there is no argument that Europe needs an independent launcher capability, the unfortunate effect was that the science program had to use the Arianes and could not freely negotiate a favorable price. This changed only after the first Ariane 5 disaster when in the case of the Cluster reflight a Russian launcher could be used. After a commercial arrangement was concluded between Ariane Espace and the Russian Space Agency for the former to market the Soyuz rockets, it became possible for the science program to obtain these launchers, which for smaller missions were much more cost effective. For large missions, like Rosetta, XMM-Newton or Herschel-Planck, the Ariane 5 is an excellent launcher.

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An important aspect of the ESA Convention is that it specifies the science program as a separate mandatory program. All countries who are members of ESA have to participate and contribute generally in proportion to their GNP. From time to time the Council of Ministers establishes the overall financial envelope. While that envelope is far from satisfactory, the separate nature of the program has had a protective effect. It made it impossible to transfer science funding into other branches of the organization when shortfalls occurred there. By 1980 the ESA Convention had been appropriately ratified by the parliaments of the member countries, and it became time to start defining a coherent long range plan for space research. Serious work on this began when Roger Bonnet became director of the ESA Science Program. It was his decision that this would not be a plan devised by some wise men, but it would be created by the community. So in 1983 a sollicitation went out to the wider scientific community for mission “concepts” which resulted in 67 responses, of which 37 were for solar system research. A survey committee was set up, chaired by Johan Bleeker, composed of 15 scientists supported by 21 scientists in “topical teams” with the task of constructing the outline of a program for the period 1985-2004. The program would be based on the input from the community, and its elaboration would take into account, apart from scientific quality – the sine qua non, flexibility, continuity, balance between disciplines, technological content and financial realism. Some missions – Giotto to Halley’s comet, Ulysses to study the solar wind, Hipparcos to measure accurate stellar distances, ISO, the Infrared Space Observatory and participation in the Hubble Space Telescope – which had previously been approved were included in the overall program “Horizon 2000”. It was clear from the beginning that a budget increase was needed to realize Horizon 2000. In fact, an annual increase of 5% above inflation was agreed to by the ESA member countries from 1985 onward till 1994 – leading to a cumulative increase of around 60%. Unfortunately, the diminishing willingness of some of the ESA countries, in particular first the UK and subsequently Germany, to invest in space and in science led to a decline of 3% per year immediately thereafter. As in the English nursery rhyme: “The Duke of York with all his thousand men he marched them up the hill and marched them down again.” By 2004 the science program had lost 21% in real income compared to 1995 to arrive at a budget of 371 M€, only a quarter more than the totally inadequate budget of 1983. The contrast with the US situation is pathetic. The NASA budget for space science in 2004 is 3971 MUS$ corresponding to 3300 M€, with the proposed 2005 budget 4.2% higher again, well above inflation. The sum of the NASA items “Astronomical search for origins” and “Structure and evolution of the universe” are twice as large as the total European spending on space science (see Note 2).

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The Horizon 2000 program3) (Figure X, 1) was based on four “cornerstones”, large missions with long lead times of much importance in their respective disciplines, as follows: – XMM, a large MultiMirror X-ray telescope optimized for X-ray spectroscopy, now “XMM-Newton” – FIRST, a Far InfraRed Space Telescope, now “Herschel”; – Rosetta, a mission to the nucleus of a comet, including a lander; – STSP, the Solar Terrestrial Science Program, composed of two parts: Cluster, an array of four magnetospheric satellites, and SOHO, the Solar and Heliospheric Observatory. The STSP was an artifact which allowed the concept of four cornerstones to be maintained without forcing a choice between the solar and the magnetospheric communities. In reality it consisted of two medium sized missions. In addition, the program included medium sized missions – in part those already previously approved and in part missions to be selected later so as to retain flexibility. The cornerstones were to be fully autonomous European missions, though SOHO became a joint ESA-NASA enterprise. A typical cornerstone would be cost capped at twice the plateau of 200 MAU (1983 value) foreseen for the annual budget of the Science Program†. The M (medium sized) missions were to cost one such annual budget, the program to end with as yet unspecified four (or perhaps five) missions M1 – M4. By the end of the 1985–2004 nominal period of the Horizon 2000 program most missions foreseen had been executed, though the FIRST/Herschel cornerstone and the Planck M3 mission had been delayed to 2007. Also M4 had not been implemented, but in a way became Cluster II, following the destruction of Cluster I on the maiden flight of Ariane 5. The high cost ISO had effectively become a cornerstone. Several missions were extended beyond their nominal two year duration (Figure X, 2), which had a negative impact on the financial situation, though it greatly increased the scientific returns. There are not many 20-year programs in science that have been executed so faultlessly through a variety of misfortunes. An update of Horizon 2000 for the next ten years was requested by the 1992 Council of ESA at ministerial level. This led to Horizon 2000-Plus4) – a roll-forward of the earlier program. This time 101 mission ideas were generated by the scientific community, 39 in solar systems science, 32 in astrophysics and 30 in physics in space. The survey committee, which I chaired, and its associated working groups totalled 75 scientists from outside ESA. This time three new cornerstones were selected: – A mission to Mercury, now named Bepi Colombo; – LISA, a Large Interferometric Space Antenna to study gravitational waves; † The AU (Accounting Unit) was an ESA financial construction which via the ECU was replaced by the Euro.

Figure X, 1. The Horizons 2000 Program as adopted in 1995. The Mercury cornerstone is now envisaged as a cooperation with ISAS (Japan), and the gravitational wave observatory LISA with NASA. The Interferometry Observatory will be the astrometry mission GAIA, but could also include a share in an infrared interferometer (DARWIN) aimed at the direct detection of earth-like planets. The M-missions – now in part “flexi-missions” at reduced cost – include “Planck” (Cosmic Microwave Background), Mars express, Venus express, ESA share in JWST (next space telescope), and Solar Orbiter. The small missions include now SMART-1 (technology demonstration + lunar science), a share in the French COROT (exoplanets) and Microscope (test of equivalence principle), and Double Star, a magnetospheric mission with China. The IR and X-ray observatories were “green dreams” for an undefined future. Recently, Horizons 2000 has been rebaptized “Cosmic Vision”.

Year 1 9 9 0 CLUSTER DOUBLE STAR ULYSSES SOHO SOLAR ORB

2 0 0 0

2 0 1 0 MAGNETOSPHERE HELIOSPHERE SUN

GIOTTO ROSETTA

COMETS

HUYGENS MARS EXP

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VENUS EXP BEPI COLOMBO SMART-1 PLANCK HERSCHEL ISO

IR

ODIN JWST HIPPARCOS COROT GAIA

VISIBLE

HST IUE

UV

ROSAT XMM-NEWTON

X-RAYS

BEPPO SAX INTEGRAL

γ-RAYS

AGILE LISA MICROSCOPE

GRAVITY

Figure X, 2. European Astronomy in Space. Missions in various scientific areas are indicated as follows: — ESA satellites; — ESA missions in cooperation with U.S., Russian (INTEGRAL), Japanese (B. Colombo) or Chinese (Double Star) space agencies; — major non ESA European satellites; — ESA cooperation with national European missions. Duration of current and future missions have not necessarily been formally decided. Qualitative indications of the main subjects are on the right hand side. The present program still appears to exceed current resources and so some delays in future missions are possible.

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– An interferometry mission, either astrometric (GAIA) or infrared for high angular resolution studies of astronomical objects, including the search for earth-like planets, the latter now named Darwin. While GAIA was given a slight edge, a priority decision would be taken some years later after further studies. M3 and M4 the two still undefined M-missions of Horizon 2000 would be supplemented by another four of the same class. In the Horizon 2000-Plus survey committee much discussion took place on possible planetary missions. At the time of the development of Horizon 2000 the situation had been very different. Both the US and the USSR had been engaged in a substantial and costly program of planetary exploration: The US had launched sixteen and the USSR an even larger number of planetary missions, though with a higher failure rate. The main targets had been Mars and Venus. A few missions had aimed at Jupiter and beyond, while also Mercury had once been visited. A very large number of missions had been sent to the moon. So it had been concluded that for Europe there were only limited opportunities in the planetary area except perhaps in certain niches. One such niche concerned comets and a flyby of comet Halley in 1986 had already been decided. Thus, in Horizon 2000 another cometary mission, Rosetta, had been included. In the meantime, consultations with the US had resulted in the M-1 mission Huygens to Titan, the major satellite of Saturn, as an adjoint to the large NASA mission Cassini to the planet. Apart from the difficulty in seeing where a European planetary mission could fit in, undoubtedly also scientific attitudes played a role. As a report of the European Science Foundation and the US National Research Council5) states: “A mission on the scale of Marsnet or Intermarsnet might not have attracted sufficient support in Europe as a cornerstone because of the inbred commitment of a majority of European space scientists to experiments on small bodies, particles and fields, and dust.” Moreover, “Averaged over all of Europe, the European astrophysics community is considerably stronger and more cohesively organized than its planetary science community”. In the meantime the planetary programs of both Russia and the US had developed much more slowly than foreseen. In Russia the political transformation reduced the importance of the space program. In the US the very high costs of the Galileo (to Jupiter) and Cassini missions, the shuttle disaster in 1986 and the cost of the Space Station very much diminished funding for other planetary ventures. So new opportunities opened up for European scientists who wanted to be part of the planetary exploration programs. When the Horizon 2000-Plus committee discussed the future plans for ESA, the issue of planetary research came again to the fore. It was clear that missions to Jupiter and beyond could hardly be considered. The solar energy flux at 5 AU would be too feeble for effective electricity generation by photocells, while suitable RTGs (Radioisotope Thermoelectric Generators) had not

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been developed in Europe. Moreover, their utilization would risk much ecolopolitical fallout. So the issue became which of the terrestrial planets to choose. The most attractive choice seemed to be Mars. As the committee stated6) “There is worldwide consensus that gives Mars the highest scientific priority among the inner planets, due to its outstanding interest for comparative planetology. The planet is smaller than the Earth, but nevertheless shows enough similarity for many geological and atmospheric processes to provide interesting comparisons and tests for theories regarding terrestrial processes.” Nevertheless, the majority of the committee selected a mission to Mercury as the next planetary cornerstone! The ostensible reason was that7) “the loss of NASA’s Mars Observer in 1993 and the programmatic uncertainties both at NASA and in the Russian program cast much doubt on the realization of the plans made some years ago” and that “In such a fluid situation, it is impossible to specify a well defined ESA Mars mission; in any case international cooperation will be required. All that can be done at this time is to specify a priority for a meaningful substantial participation when the opportunity arises. This priority should be such that other items in the ESA planetary-science program may have to be rearranged.” Is Europe unable to specify a major Mars mission on its own, especially when the misfortunes of the others had left the field wide open? Following a brief discussion of the fact that relatively little was known about Mercury, the committee went on to propose a cornerstone mission to that planet. It was the only issue about which it had been necessary to have a vote; on all other items a consensus could be reached. Apart from concerns about where an ESA mission to Mars could fit in, the advantage of Mercury was that it was a planet with a magnetosphere. So there was something in it for two communities. Moreover, no new missions in the terrestrial magnetosphere were foreseen, so for that still powerful community it was Mercury or nothing. There is no doubt that a mission to Mercury had a high scientific interest*. But it does not have the much broader appeal of the Mars missions: climatologists, geologists and biologists all would benefit from the study of Mars. Moreover, one has seen several times the incredible enthusiasm of the general public for Mars missions. While one cannot base a science program on this, it is, nevertheless, a significant fringe benefit. Support for science requires funding and public support is helpful in obtaining this. The unfortunate consequences became evident very quickly. Both the French and the Italians decided to seek participation in the NASA program. So, instead of having a vigorous European program of Mars exploration, Europe would again be dependent on priorities set elsewhere. In 2000 the French CNES, * In the meantime NASA has launched in 2004 the Messenger mission to Mercury which should from 2011 onwards map the uncharted part of the surface and measure its magnetic field. Is the ESA mission with arrival in 2016 still equally interesting?

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prodded by research minister C. Allègre, announced the plan to place in 2007 (in cooperation with eight other countries) four small landers on Mars for seismological, mineralogical and climatological observations. However, in April 2003 (coincidence?) NASA suddenly pulled out of the venture8). A month later, France cancelled the whole project and also withdrew its support for the unrelated US gamma-ray mission GLAST9). The French also announced that future Mars exploration would take place only in the ESA context. In part the French decisions resulted from a long overdue analysis of the CNES finances. The uncertain prospects for space funding in Italy have also made its participation in NASA’s 2009 Mars missions quite uncertain. In the meantime, other factors led to the renaissance of a European Mars program. Many laboratories had been building instruments for the Russian Mars-96 mission, which unfortunately ended in the Pacific Ocean. Spares of several instruments were available, and so a relatively cheap and fast mission was in ESA’s reach. This became Mars Express, successfully launched in 2003. Moreover, with spending on the Space Station tapering off, ESA began to also consider what to do next in manned space flight. The result was “Aurora”, to investigate the possibility of placing a European on Mars. While the question may be asked what that European would do there, this could lead to more vigorous preparatory missions to Mars. “Aurora” was formulated some two years before the corresponding widely publicized US proposal in 2004. It is presently outside the Science Program of ESA and thus depends on non mandatory financial contributions from the ESA member states. So it seems that the recent political tensions and more accidental factors may finally lead to a more unified, coherent European Mars program. However, much will depend on the funding decisions for “Aurora” during the coming years. Of course, cooperation with Japan, Russia and the US in the Mars program is also a good thing, but only if there is first a clearly formulated program in Europe. In the meantime the US program on the Moon and Mars is beginning to take on gigantic proportions, with the expectation that this will necessitate the end of the Space Station. If so, what have the Europeans gotten out of their participation in the latter? Several thousand million euros down the drain without any return? It never looked a cost effective venture from any point of view, neither scientifically nor industrially. But a unilateral decision to terminate it would also show that Europe should not enter again in such a large project with the same partner. Why not learn one’s lesson and develop a sophisticated, technologically challenging robotic program? The spin off to industry could be very large. And when finally the first American stands on Mars in 2030 waving a flag, while worrying about his return, Europe could have a considerable remotely controlled presence there at a fraction of the cost. The astronaut could even be welcomed by a robot waving a flag with a circle of 12 stars. Following the adoption of Mars Express, a mission to Venus also found its way into the program. Since much of the spacecraft would be the same

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as for Mars Express, such a mission would be relatively cheap. Nevertheless, Venus Express went through a cycle of approval, cancellation and resurrection all within a year. Launch is now foreseen at the end of 2005. The Space Station also figures in the Horizons 2000 program. Proposals have been made to place there EUSO, an instrument to observe radiation from very energetic cosmic rays hitting the earth atmosphere, and Lobster, an all sky X-ray monitor. However, the future of the Space Station for scientific research is now so uncertain that serious planning is difficult. It had also been envisaged to assemble a large X-ray facility, XEUS, at the Space Station and subsequently to place it in an independent orbit. In the meantime XEUS is envisaged as an independent mission to be placed at L2. The result of the two exercises, referred to as “Horizons 2000”, was to cover the period till 2017 (Figure X, 1). The Horizon 2000-Plus program was based on a constant budget (corrected for inflation) through 2000, 5% annual increases in the years 2001–2005, followed by constant budgets at the 2005 level. The ministerial Council of ESA in 1995 approved the Horizon 2000-Plus program, but deleted the increases for the 2001–2005 period. Instead it imposed the budget reduction of 3% per year mentioned before, followed by a flatter budget a few years later. As a result, the approved program was seriously out of balance. As the financial circumstances deteriorated, this led to a number of reshuffles of the program. The final result, however, preserved all the elements of the program: The six unallocated M-missions became Planck – to study the cosmic microwave background – Mars express, Venus express, the JWST participation, Solar Orbiter and the reflight of Cluster. The interferometric cornerstone was transformed into GAIA (no longer interferometric). The small missions became the technology demonstration mission dubbed SMART-1, and ESA contributions to two French missions, now internationalized, COROT for asteroseismology and to look for planets and Microscope to test the Einsteinian principle of equivalence, and Double Star, an ESA cooperation with China in magnetospheric research. In a wave of optimism the reserve medium mission Eddington, which was to study asteroseismology and occultations of stars by exoplanets, was added to the program but removed again less than two years later much to the chagrin of the community that had just been built up around the project. Perhaps it will be revived in the future. It may seem surprising that with diminished resources the full program could still be executed. However, a number of factors have allowed significant cost reductions in both cornerstones and M-missions. Grouping of missions to have commonality of the space platforms and other resources, new technologies and international cooperation all contribute to this. The Mercury mission now will have a Japanese component and LISA will be a joint ESA-NASA mission. New technology reduced the projected weight of GAIA, allowing a launch with a Soyuz-Fregat, which is also the launcher of choice for several other missions at substantial savings. While it has been possible

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to squeeze the various missions into the Horizons 2000 program with a reduced budget, this has increased the dependence on international partners, taken all flexibility out of the program and left little room for adjustments for contingencies. The time lines of the major elements of the program are shown in Figure X, 2. A few large national missions are also included in this figure. More detailed descriptions of individual missions are provided in chapters VIII and XI - XV. A new director of the ESA Science Program having arrived, Horizons 2000 had to get a new name: “Cosmic Vision”. It may be asked if the budget driven cost reductions are realistic. At NASA the “faster, cheaper, better” was pushed very far, and the results have been mixed. Some cheap missions were very successful, but others ended in failure. New technology is helpful, but, nevertheless, there are limits as shown by the Next Generation Space Telescope. As it went from early design to hardware contract, the diameter was reduced and the cost increased substantially. Until now the ESA scientific satellites have had a nearly perfect record, and a valid case may be made that a significant cost reduction with the increased risk of an occasional failure gives the best cost-to-benefit ratio. The success of the Mars Express orbiter and SMART-1 contributes to confidence in the realism of the overall program. An indication of the updated costs of the ESA missions is given in Figure X, 3. The precise meaning of the inflation corrections is open to argument, especially over periods of more than a decade. ESA’s science budget is in reality smaller than it seems because of various constraints built into the system. The most serious of these is the principle of “juste retour”. Each member country obtains industrial orders in proportion to its contribution. It is understandable that in the very beginning, when space industry was not yet developed in some countries, one would have given favorable treatment to the “have nots”. But by now it is a rather inefficient system. At every ministerial meeting the situation is further aggravated by a further increase in the minimum cumulative return percentage. The result is that one has to place industrial orders that one knows to be uncompetitive, and that the offers from the major enterprises include inefficient subcontracts for the sole purpose of having the right industrial return percentage. In view of the continuing effort of the European Union to combat anticompetitive practices within the Union, the whole arrangement seems anachronistic. It is generally thought that “juste retour” adds some 20% to costs, but I believe this may be an underestimate. It also may affect the effective rate of inflation. An important difference between the nature of ESO and CERN on the one hand and the ESA science program on the other should be noted. The former are built around one dominant project. For ESO during the last decade the VLT was the absolute priority, scientifically and financially. Similarly at CERN everything else has to make way for the Large Hadron Collider. Budgets for these projects have been set at the beginning and determine future overall spending by these organizations. At ESA it is different.

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Figure X. 3. Major ESA Science Missions launched or planned after 1980. Costs in M€ have been updated to 2004. They include capital costs and operational costs during the mission. Completed missions are indicated in red, current missions in green and planned missions in blue; in cooperative missions, only ESA costs are included. Instrumentation costs borne by the member countries are not included.

It executes a program of missions within a certain financial envelope. So there is competition between the solar, planetary, infrared, optical, X- and gammaray communities which each obtain a spacecraft from time to time with long intervals inbetween. Balance is the key word in the ESA Horizons program, while ESO and CERN are concentrated around one aim at a time. As a result, they have a much stronger scientific identity. One other aspect of the ESA Horizons program is important. While ESA provides the spacecraft, interfaces and mission operations, almost all scientific instruments are made in institutes in the member countries and paid for by those countries out of national space budgets. In the nineties, this payload support typically has amounted to 50–70 M€ annually, corresponding to some 20% of the budget of the ESA science program, with part of the personnel expenses still to be added. However, more recently it has become lower, with some of the member countries even asking ESA to choose between an inadequate payload and a partial ESA financing for its realization! Most instruments are constructed by multi-institute cooperations headed by a Principal Investigator (PI) (Table X, 1), whose country usually pays a

Mars

+

+ +

+

+ ++

++ ++ ++

Venus

+

++ ++ ++ +

Huygens

++

+

+ ++

Smart-11)

+

+

+ +

+

Giotto +

+

++

+++ ++

Rosetta ++

++ + ++

+

+++ +++ ++ ++ +

Ulysses +++

+

+

++

Cluster +

+

++ +

+ ++

SOHO ++

++

+

+

++ +++

EXOSAT +

+

XMM +

++2)

2)

INTEGRAL +3)

+3)

+

+

+ +

+

+

+ +

+

+

+

Herschel

Only science instruments. 2) One originally I, later changed to UK because PI assumed other function. 3) CH: Science Data Centre, Rus: proton launch, Russian data center. Note: European institutes have also made instrumental contributions to non ESA missions. Among the larger ones we mention the French SIGMA and FREGATE to Russian – respectively NASA γ-ray missions, the German COMPTEL and the Dutch-German LETG (spectroscopy) to NASA γ-ray respectively X-ray missions, the UK Bragg Crystal Spectrometer and the Large Area Proportional Counter to the Japanese Yohkoh (solar) respectively Ginga X-ray missions. The Swiss contribution to RHESSI (solar X-rays) and the French one to FUSE (uv spectroscopy) also were important. In addition, a variety of European institutes contributed to magnetospheric and heliospheric missions by other agencies. Instruments for national missions in Europe have included the UK EUV camera and the NASA high resolution imager for ROSAT (D), and the Dutch wide field X-ray cameras for BeppoSAX (I).

1)

D F I UK A B Dk SF Ei NL ESP S CH Hun Rus US

ISO

Table X, 1. PI countries on ESA missions. One PI is indicated by +, two or three by ++, and more by +++.

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substantial part of the cost, but the co-investigators’ countries also contribute. From the table the broad participation and the differing interests of some of the ESA countries are apparent. On average, the instruments on the solar system missions have been more numerous and less expensive than those of the astronomical observatories. In solar system missions the tradition has been that the scientists who have constructed an instrument are the “owners” of the data it produces. In the astronomical observatory missions the instrument providers obtain a certain fraction of the observing time – typically 30% initially, and somewhat less later on. The remainder is distributed to scientists who propose observing programs which are evaluated competitively. This is entirely appropriate since the cost of the instruments is generally substantially less than the cost of the mission as a whole, which is borne by the whole ESA community. Sometimes different procedures are followed; for example in Hipparcos the complete satellite was provided by ESA, since a meaningful separation of instrument and spacecraft was not possible. However, two large consortia of scientists performed the complex analysis of the data and thus also had a first look at the data.

Conclusion The Horizons 2000 program has been an undisputed success. It has given a relatively stable frame to European space research with the scientists in the various subdisciplines knowing what to look forward to on a decadal time scale and to prepare themselves adequately for maximizing the returns of the missions. Of course, the long term planning also has a negative aspect: reduced flexibility. It was thought that some of the flexibility could be provided by the national programs, and in the nineties this was, in fact, the case. However, the reductions in national spending have largely put an end to this complementarity. It is not only the flexibility that risks being lost, but also the intervals between the missions have become so long that it is difficult to have enough continuity, especially for students and postdocs wishing to work in these fields. X-ray astronomy is an example. After the end of EXOSAT in 1986, it took 14 years before XMM-Newton started taking data. That European X-ray astronomy was not more seriously affected is the result of the national missions of ROSAT and BeppoSAX which bridged the gap. When the national missions become less frequent, such gaps in the ESA program will become still more damaging.

XI. European Space Missions: IR, X- and Gamma Rays

But time is short and science is infinite – how infinite only those who study astronomy fully realize - and perhaps I shall be worn out before I make my mark. Thomas Hardy1)

The visible–near infrared radiation observable from the earth’s surface represents only a very narrow slice of the electromagnetic spectrum (Figure I, 4). The IR above 2.5 μm is largely unobservable from the ground, though there are some limited “windows”. Below 0.3 μm the atmosphere is opaque. Astronomers have been lucky that common stars, like the Sun, emit most radiation in the 0.3–2.4 μm accessible interval. So stars and galaxies could be observed from the ground and a certain picture of the Universe obtained. However, many essential aspects remained hidden. Much of the energy of galaxies is emitted in the far IR, the cosmic microwave background is mainly around 1 mm, and also, for studies of the interstellar medium, star and planet formation only in the IR can the all pervading dust absorption be overcome. X- and γ-rays contain much of the information about the hot, high energy Universe, on the largest mass concentrations – the clusters of galaxies – and on black holes. So just a view of the Universe in visible light would remain terribly incomplete or even erroneous. Most observations of the IR, X- and γ-rays have been obtained with satellite based instruments. Useful observations may also be made with high altitude balloons or with week long shuttle flights. It would lead us into too many details to discuss all of these here. In this chapter we briefly review recent and future European space science missions in the Infrared, X- and Gamma-Rays. Optical and near IR space telescopes are discussed in chapter VIII, missions in the Solar System in chapters XII and XIII, studies of Cosmic-Rays and Gravitational Waves

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in chapter XIV, and searches for Exoplanets in chapter XV. In several chapters related ground based activities are also included.

Infrared / mm From the ground observations are possible from the visible to 2.5 μm and again upwords from 1 mm. While there are some “windows” in between (Figure XI, 2), the atmosphere is nearly completely opaque from 30 to 300 μm. Moreover, telescopes and mirrors at ambient temperatures are powerful radiators over much of the IR, and so is the atmosphere. The resulting background very much reduces sensitivity. While for some purposes it is possible to observe from the 4 km high plateaus at the center of Antarctica or from high flying aircraft and balloons, the only fully satisfactory solution is to go into space and there to cool everything that may radiate into the detectors. The first cryogenic satellite devoted to IR astronomy was IRAS – the InfraRed Astronomical Satellite, a US-NL-UK cooperative venture. In 1983 it made a six month survey of 97% of the sky. IRAS resulted from plans in the Netherlands in 1974 for a successor to the ANS satellite (Astronomical Satellite of the Netherlands) and from an Announcement of Opportunity for an Explorer class mission by NASA. With its 57-cm telescope and some 60 detectors cooled to 3 K it performed photometry in broad bands centered at 12, 25, 60 and 100 μm wavelength. Some 250,000 sources were catalogued, mainly stars but with nearly 10% galaxies. IRAS also had a low resolution spectrometer. Some earlier observations of known optical objects had been made in the mid-IR with balloons and rockets. The importance of IRAS was that it made an unbiased survey which allowed it to discover sources that were strong in the IR, but inconspicuous in the visible. Most notable among these were galaxies that radiate in the IR up to a thousand times as much energy as our Galaxy radiates at all wavelengths. Such galaxies have very high rates of star formation, but dust prevents most of the visible radiation from reaching us. While IRAS detected many sources, its four broad band detectors were insufficient to gain detailed spectroscopic information. So already in 1978 some scientists made a proposal to ESA for a 1-m cooled IR telescope. Ultimately, this led to ISO2) (Figure XI, 1), the Infrared Space Observatory, which was launched on 17 November 1995. With its 60-cm mirror it was no larger than IRAS, but its instrumentation was far more powerful, with imaging cameras and spectrographs of various angular and spectral resolutions (Figure XI, 2). The ISO instruments covered the wavelength range 2.5–240 μm. At the shortest wavelengths the angular resolution was a few arcseconds, but at 200 μm the diffraction at the small mirror limited it to

Figure XI, 1. The ISO satellite. The liquid helium, which slowly evaporates, cools the telescope to 3K above absolute zero temperature (– 270 °C) and some of the detectors to 2 K. Just behind the 60-cm primary mirror of the Cassegrain telescope is a pyramidal reflector which sends the light into one of the four instruments. The star tracker keeps the telescope pointed towards the target. The service module contains units for telemetry and other housekeeping tasks.

R 106

104

100

1

10

100 wavelength

μm

1000

Figure XI, 2. Spectral resolution (R) and wavelength ranges of the instruments of ISO (–), Herschel (–) and the NASA SIRTF (–). The main wavelength ranges inaccessible from the ground are indicated by grey areas in the upper part of the diagram; however, in the three windows between 3 and 12 μm the atmospheric background is too strong for very sensitive observations. The windows beyond 300 μm may be observed with APEX and ALMA (chapter IX). The HIFI instrument on Herschel may be used at resolutions from 106 down to 103. The duplication between ISO and Herschel in the 80–230 μm range is only apparent, since the angular resolution of the latter is six times better.

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about 3 arcminutes. The four instruments of ISO were multifunctional and, as a result, quite complex (Figure XI, 3). However, they functioned almost faultlessly. Contributions to their construction were made by laboratories in most ESA countries. There were two imagers (with also spectroscopic options), ISOCAM (F) and ISOPHOT (D), and two spectrographs, SWS (NL) and LWS (UK), with the principal investigators from the countries indicated; these also paid for the larger part of the costs of the instruments. All instruments were extensively used : ISOCAM 28% of the time, ISOPHOT 30%, SWS 24% and LWS 18%. During the operational phase of ISO, contributions were also made by Japan and the US, which increased the total observing time by making additional ground station facilities available. ISO presented a number of difficult technological problems. All the mechanisms for moving wheels with filters and other items had to function in the extreme cold environment. But probably the most difficult was to obtain the required very sensitive, low noise, detectors. Thanks to its enormous military budgets, industry in the US has generally had a significant advance over Europe in detector technology and production. This was particularly so in the infrared where night vision devices were in much demand. While these detectors were available to US scientists, they usually could not be exported. The game played by the Americans was to see what was made in Europe and then “declassify” something just a bit better. This served to discourage European industry, except when governments (especially in France) took matters in hand to avoid too strong a dependence. As a result,

Figure XI, 3. The layout of ISOCAM. The light beam enters the camera through the entrance wheel, which in some positions has polarizing optics. It is then reflected by mirrors on the selection wheel and subsequently passes through filters and lenses on other wheels. These allow the selection of different wavelength ranges and image scales. Many different combinations are possible.

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the ISOCAM camera, built in France, for the 2.5–17 μm range had two detector arrays of 32 × 32 elements, while substantially larger arrays already existed in the US. Sensitive detectors at the longest wavelengths became available very late during the development of the ISOPHOT cameras built in Germany, so that not much time remained for testing. In orbit it turned out that while the sensitivity to infrared light was excellent, the same was the case to charged particles. Though ways were found to mitigate these effects, it remained an unpleasant problem. ISO may well have been the most expensive mission in the ESA science program. Updating costs to year 2004 euros and including national contributions for instrumentation, I would estimate that the overall cost amounted to nearly 1000 M€, with the instrumentation accounting for 20–30% of the total. The costs were high, but the results impressive. The mission lasted more than two years until the helium was exhausted. During this time some 26,000 observations were made for projects involving 550 scientists as PI’s. Targets ranged from the planet Mars to the most distant galaxies in the Universe. Results included the discovery of water throughout the Universe, from the atmosphere of Saturn’s moon Titan to distant galaxies. The composition of the dust disks around numerous stars was analyzed and similar dust properties were found in comets and around some stars, reinforcing the belief that planets may be forming in these disks. Ices of water, CO2, CO, methane and others have been studied in the cold envelopes of very young stars. Characteristic PAH (polycyclic aromatic hydrocarbon) bands due to small dust particles (a few hundred molecules) were extensively observed and in galaxies seem to be associated with star formation. Molecular hydrogen, a dominant constituent of interstellar matter, was also studied in many places; this is important since usually the H2 abundance was inferred from the intensity of the CO lines in the radio spectrum with an assumed H2/CO ratio. The interstellar gas is heated by stars and cooled by emission lines, the most important being the ionized carbon line at 158 μm, fully within ISO’s reach. In dust rich galaxies the structure becomes much clearer in the midIR (Figure XI, 4). Emission lines of highly ionized elements indicate the presence of quasar-like nuclei hidden in galaxies by dust (Figure XI, 5). Deep surveys in selected regions have taught us much about galaxies in the distant, high redshift, Universe. Both galaxies and quasars of high luminosity were more abundant, presumably because encounters between galaxies were more frequent in the higher density Universe. A number of lessons have been learned from the ISO experience. Initially, the overall software effort needed in the Scientific Operation Center had been grossly underestimated. This had been based partly on the EXOSAT experience. However, that X-ray satellite was far less complex, suffered fewer orbital constraints and had observations of much longer duration. As a result, early in 1994, well before operations began, the projected manpower requirement had to be almost tripled. The SOC had both ESA manpower and staff

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Figure XI, 4. The Whirlpool Nebula M51. At visible wavelengths the spiral arms are very thick and dust absorption occurs almost everywhere, complicating the interpretation of the image. In the ISO image around 15 μm dust absorption is no longer important and the spiral arms are very clearly defined. The emission is mainly due to dust heated by very active star formation. Tidal effects due to the associated galaxy NGC 5095 (to the left of M51) perturb the outer arms of M51.

provided by the participating institutes. This mix of people who had been involved in the construction of instruments and others who interfaced with the users, functioned very well. All instruments were multimode. While each mode had a certain scientific justification, it required a non negligible software effort for its implementation. So even with the increased manpower, the number of modes offered had to be reduced to 24. However, at the end of the mission it appeared that 9 modes in ISOPHOT had been used in total for only 2.5% of the available time. A stronger concentration on the most essential modes could have saved money, increased reliability and allowed a more efficient use of the available manpower. The ISO orbit (1000–70 000 km high) involved many constraints. The sun, the moon and the earth had all to be avoided by a fair angle so as to avoid stray light. This limited the accessible part of the sky at any particular moment, which complicated the scheduling process. The observing time proposals had received quality ratings of 1, 2, or 3 in the evaluation process.

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Figure XI, 5. ISO spectrum of the nearby Circinus Galaxy. Spectral lines due to singly ionized silicon, neon and others are emitted by gas ionized by a recent burst of star formation. But lines of eightfold ionized silicon (Si IX) demonstrate that a quasarlike nucleus is hidden inside the galaxy. Photons with an energy of 303 electronvolts (0.0041 μm) are required to ionize the Si. Stars hardly emit any such photons.

Frequently, these operational constraints made it necessary to fill the time with priority 3 proposals. Future satellites placed at L2, at 1.5 million km from the earth in the antisolar direction will avoid these troubles. ISO was a great success as the world’s first observatory mission in the IR. However, at longer wavelengths its angular resolution was very poor due to the small diameter of its mirror. The next ESA mission in the far IR should improve on this and also cover the remaining wavelength range beyond 200 μm. The Far Infrared Space Telescope, Herschel3) (earlier baptized FIRST), to be launched in 2007, will have a mirror of 3.5 m (Figure XI, 6). Both the telescope and the mirror will be made of silicon carbide, a material with a favorable strength over weight ratio. At the longer wavelengths radiation from the telescope and mirror is a lesser problem, and it will be sufficient to passively cool these to some 80 K. This can be achieved by the radiative heat loss towards space because Herschel will be placed around L2, where the heat radiated by earth and moon is unimportant, while a shield

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prevents heating by the Sun. Cameras and spectrographs will cover the wavelength domain of 60–670 μm. The detectors again will have to be cooled to below 2 K by superfluid helium. Beyond 300 μm ground based observations become possible at some wavelengths, and here ALMA with its superior sensitivity and angular resolution will begin to take over, though between 300 and 670 μm many gaps remain where only Herschel has access (Figure IX, 6).

Figure XI, 6. Herschel (left) and Planck (right) are to be launched in 2007 with one Ariane-5 rocket. Herschel will be an observatory for the 60–670 μm domain with imagers and spectrographs (Figure XI, 2), while Planck will scan the sky to determine the intensity distribution and polarization of the Cosmic Microwave Background, the relic radiation from the Big Bang. It will observe the sky in 9 channels at wavelengths from 0.35–10 mm. The instruments of Herschel will be cooled to 1.7 K, some of those of Planck to 0.1 K. Both will be placed at L2. So the Sun, earth and moon are close together in the sky and the opposite hemisphere is free from their IR radiation. In the upper part of the left image the 3.5-m Cassegrain telescope is seen, behind it the cryostat filled with liquid helium which envelops the instrument, and below the housekeeping unit. Planck’s 1.5-m mirror is seen on the right in an arrangement which minimizes star light.

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Herschel in space and ALMA on the ground are very much complementary missions. The two main areas of research of both are the same, but at different wavelengths different aspects come to the fore. The cost of the two is comparable: of the order of 600–700 M€. But, of course, after a few years the helium in Herschel will be gone, while ALMA may continue to function for decades. Herschel will have three instruments : PACS (D), SPIRE (UK) and HIFI (NL) with the PI countries as indicated. Again, important contributions are made by laboratories elsewhere. PACS is a broad band imager for the 60–210 μm spectral region and SPIRE for the 200–670 μm domain. Both also have a spectrometer for low to medium resolution spectroscopy. HIFI is a very high resolution instrument based on heterodyne techniques and able to attain spectral resolutions of up to 1,000,000 in some bands in the 100–600 μm region. Through the Doppler effect this corresponds to a velocity resolution of 0.3 km/sec. During its 3–4 year lifetime Herschel is expected to observe a wide variety of celestial objects - in particular young galaxies in the early Universe and regions of star and planet formation in our own Galaxy with the associated chemical processes. Young galaxies and quasars in the early Universe should still be very rich in gas and dust which will obscure and absorb their visible radiation and reradiate it in the far IR. Herschel will be well equipped to find such objects, to determine the energy they radiate and to study the conditions in and the motions of the gas in these galaxies, which may give us an idea of how our own Galaxy must have looked in its early days. The formation of stars and planetary systems from the interstellar gas and dust is still rather poorly understood. In a general way, in denser regions the interstellar medium begins to contract due to its own gravity until it becomes finally hot enough for nuclear reactions to occur and a star is born. Along the way dust particles may stick together into bigger and bigger clumps which by their gravity attract more matter and become planets. During these various phases in the evolution, chemical reactions take place which lead to the formation of complex molecules which are believed to have played an important role in the evolution of planetary atmospheres and perhaps even of life. Both the dust and the molecules provide many diagnostic features in the spectra of the star forming regions which Herschel should be uniquely able to study. At wavelengths of several hundred μm there is a diffuse glow over the whole sky which is believed to be due to numerous massive galaxies in the early Universe. It is one of the tasks of Herschel to track down the origin of this radiation in detail. However, around 1 mm there is a still more energy rich glow left over from the early hot phase of the Universe – the Big Bang. The Cosmic Microwave Background has the spectrum of a perfect (black body) radiator at about 2.7 K. The CMB is extremely uniform with temperature fluctuations of no more than a few parts in 100,000. These variations

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are related to small density fluctuations in the gas out of which much later galaxies began to form. These fluctuations also contain information on much earlier times, close to the origin of the Universe. The first satellite to detect the fluctuations in the CMB was NASA’s COBE. With its angular resolution of 7° only the broadest features could be discerned, but still much progress was made4). Subsequently, much better angular resolution was obtained with BOOMERANG3) (I + US with Canada and UK), a balloon borne instrument flown over Antarctica. Structures down to 0.2 degrees were measured in a limited area of the sky which showed three peaks in the correlations due to sound waves in the early Universe resulting from initial inhomogeneities dating back to very early phases of the Universe. Further results with balloons were obtained with ARCHEOPS3) (F, I) launched from Kiruna (S) and with MAXIMA in the US. Also some ground based instruments operating at the long wavelength end of the CMB (~ 10 mm), including a UK – ESP cooperation at Teneriffe, have provided useful data. An 8-m submm telescope at the South Pole is being planned by the US. The next NASA satellite WMAP3) followed in 2001. It has five wavelength bands between 3 and 14 mm with angular resolutions from 18–54 arcminutes and is also able to obtain polarization information. In a year it reached a sensitivity of 35 μK, corresponding to a fluctuation in brightness temperature of one part in 100,000 per 18 × 18 arcmin2 pixel. ESA’s Planck mission3) aims for still higher sensitivity and angular resolution. With its 1.5-m telescope it will observe the CMB around its spectral maximum at 1 mm with a resolution sufficient to measure the smallest features expected. It will have nine sets of imaging arrays in the wavelength range of 0.35–10 mm, four with HEMT radio receiver arrays and six with bolometer arrays. These have one overlapping channel at 3 mm. The bolometers will have to be cooled to 0.1 K above absolute zero, certainly an ambitious goal in space. The broad wavelength range will allow an excellent separation between the CMB and emission from our own Galaxy by both dust and gas. At 0.8 mm (800 μm) the best angular resolution of 5 arcmin is reached with a sensitivity of 40 μK per pixel. At shorter wavelengths the sensitivity deteriorates rapidly. At 2–3 mm the resolution is still 8–11 arcmin, and the sensitivity reaches 5 μK per pixel corresponding to a temperature fluctuation in the CMB of two parts per million. Planck also has the possibility to measure polarization. This will enable us to determine the “epoch of reionization” when the first stars formed and ionized the intergalactic gas. Scattering by the resulting electrons produced low levels of polarization in the CMB. The Planck spacecraft is spinning to provide all-sky coverage at a uniform rate. With its low angular resolution (compared to Herschel) it is not the ideal instrument to study point sources. However, thousands of clusters of galaxies should be detected, which may be further studied with XMM-Newton and with the VLT. Planck and Herschel are to be launched together with an Ariane-5 rocket in 2007.

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Two other European ventures in the IR should be mentioned. In 2001 the Swedish (with SF, F, Can) satellite Odin3) was launched with 50% of the time available for astronomy and the other 50% for aeronomy. It contains a 1.1 m telescope with instruments which may obtain observations around 0.53, 0.6 and 2.5 mm wavelengths. Spectral lines of H2O, NH3 (ammonia) and O2 could be observed. The latter was not detected and unexpectedly low limits have been placed on its abundance. A smaller 60 cm telescope, SWAS3), for similar observations was launched by NASA two years earlier. Because of its larger telescope Odin has nearly twice the resolution of SWAS; its sensitivity is ten times better for point sources, and its velocity resolution up to 12 times higher. The latter was important in observations of comets where water outflow from the nucleus was mapped with 80 m/sec velocity resolution. Germany participates at a 20% level in a NASA project, SOFIA3), for a Boeing 747 plane with a 2.5-m telescope and a suite of instruments. While even at 13 km altitude the residual atmosphere presents many problems, a wide range of spectroscopic observations may be made. Of course, the great advantage is that instrumentation can be continuously updated and liquid helium to cool the detectors can be added as long as needed. The telescope was provided by Germany, which also contributes two of the nine initial instruments. Instrumentation includes cameras for the 1–240 μm wavelength range and spectrometers with resolutions up to 10 5 or 106 for 5–600 μm. SOFIA is expected to be fully functional at the end of 2005. Some 160 flights with 6 hours at altitude are expected annually. The US and Germany will separately allocate their part (80% respectively 20%) of the observing time. In 2003 NASA launched SIRTF3) – the Space InfraRed Telescope Facility, now named Spitzer. It is similar to ISO, but with newer, better and larger detector arrays. With the usual hype this is advertised across the Atlantic to be infinitely superior! However, its 85-cm telescope gives it an angular resolution not much better than ISO, while it lacks the higher spectral resolutions. But the 256 × 256 pixel camera is some 45 times larger than that of ISOCAM, and its sensitivity is also higher. However, in deep surveys at several wavelengths confusion noise, due to overlapping images, predominates. Since this depends only on the angular resolution, the advantage over ISO is not so very great, but, of course, Spitzer arrives at the confusion limit faster and over its larger area. Its orbit trailing the earth with ever increasing distance avoids some of the operational drawbacks of ISO in earth orbit. It is ironic that when ISO was started, NASA told ESA that there was no point to it, because they would be faster and so ESA better join their project. As it came out, ISO was eight years earlier and obtained several important firsts. Japan is making very rapid progress in the IR. In 1995 it launched IRTS with a 15-cm liquid helium cooled telescope which functioned for about five

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weeks, during which time it surveyed 6% of the sky. The next mission, ASTRO-F3) has been prepared for launch in 2006. With its 67-cm siliconcarbide mirror cooled to 5.8 K it will make an all sky survey in six wavelength bands in the range of 6–200 μm, with a sensitivity some 30 times better than IRAS. After completion of the six months survey, pointed observations should reach much greater depth albeit in more limited areas. A particularly ambitious project is being studied in Japan for launch around 2010. SPICA3) would be a 3.5-m telescope, optimized for the 5–200 μm wavelength range, cooled to 4.5 K by mechanical coolers. Since the telescope would be launched at ambient temperature, the weight of large quantities of liquid helium is avoided. SPICA should have unprecedented sensitivity, outperforming JWST above 15 μm, albeit at 1.6 times lower angular resolution (Figure XI, 7). It should be placed at L2. Beyond 100 μm its performance would be comparable to that of Herschel, because it has the same diameter;

zz

IR sensitivity

-15

z z z z z

z z z z z z z z z

z z

z

z

-20

10

100

μm

1000

wavelength

Figure XI, 7. Schematic view of IR sensitivities. The vertical scale give log(vFv) in w/m2, which is a measure of the energy received in a broad band around wavelength λ indicated on the horizontal scale. For the IRAS and ASTRO-F surveys the actual limiting fluxes (at a signal-to-noise ratio of 5) are indicated, for the observatory type missions those corresponding to a 1 hour observation. Source confusion and backgrounds may be very different depending on the source location and affect the sensitivities. The missions are identified as follows: — IRAS, — and • ASTRO-F, — ISO, — SIRTF, — Herschel, — JWST, ••• SPICA (still undecided) and — the ground based ALMA.

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at the long wavelengths the cooling of the telescope does not give an advantage, while source confusion may be the limiting factor for both. For the moment there is no competition in sight for Herschel. There were proposals to NASA for an 8-m telescope SAFIR3) (Single Aperture Far InfraRed) for the 30–300 μm spectral range. In the meantime it appears to have been enlarged to a 10-m telescope, cooled to 4 K for the 15–600 μm range. If JWST is an example, it may well shrink again when the real cost becomes apparent. The intent would be to launch it around 2015, but nothing appears to have been decided as yet. It could be a valuable complement to JWST, the successor to the Hubble Space Telescope. The only future project with mid-IR capabilities after ISO and Herschel currently under consideration in Europe is the 15% participation in the 6-m JWST (see chapter VIII). It should allow observations from 0.6–28 μm. Surveying the overall European program in the IR, we conclude that it has been quite satisfactory with two important firsts: ISO and Herschel, which have opened up several spectral domains never surveyed before or should do so in the near future. However, the longer term future is less evident. A summary of the world’s astronomical IR space missions is given in Table XI, 1. Table XI, 1. Infrared space missions. From left to right the columns present the (expected) year of launch, the acronym of missions of Europe, joint EU-US, US, Japan, diameter of primary mirror and smallest and largest wavelengths, followed by c for telescopes cooled to liquid helium type temperatures. IRAS lasted 10 months, COBE 4 years, IRTS 5 weeks and ISO 28 months. MSX was a military mission that produced a published Galactic plane survey. The others are in orbit or not yet launched. SPICA and SAFIR are still uncertain. More details can be found in the text.

Launch 1983 1989 1995 1995 1996 1998 2001 2001 2003 2005 2007 2007 2010 2011 2015

EU

US

Japan

IRAS

d (m)

λ (μm)

0.6

12–100 1–9500 3–800 3–200 4–22 530–620 500–2500 3000–14000 3–200 6–200 60–670 350–10000 5–200 0.6–28 30–300

COBE IRTS ISO MSX SWAS Odin (S) WMAP Spitzer ASTRO-F Herschel Planck SPICA JWST SAFIR

0.15 0.6 0.35 0.6 1.1 0.9 0.7 3.5 1.5 3.5 6 10

c c c c

c c c c

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X- and Gamma-rays While the impetus for ISO and FIRST came from the astronomical community, the first push for X- and gamma-ray missions came from cosmicray physicists who were familiar with the necessary instrumentation and intrigued by a possible gamma-ray component in the cosmic rays. During the seventies some small European satellites were launched with X-ray detectors, including two by the UK (Ariel 5 and 6) and one by the Dutch (Astronomical Netherlands Satellite No 1). Also the Japanese Hakucho satellite performed well. Beginning in 1970, NASA launched some six X-ray satellites of ever increasing performance, until 1978 when “Einstein” with its focussing optics revolutionized the field. The fundamental problem of X-ray astronomy was that the types of telescopes that are used for visual light cannot function at very short wavelengths. At nearly vertical incidence the X-rays would be absorbed or scattered rather than reflected. However, at very low angles (~ 1 degree) the situation is different and appropriate metallic surfaces reflect very well. Of course, this means that we cannot employ Cassegrain telescopes. Instead it is possible to obtain images by having the X-rays reflected first by a paraboloidal and subsequently by a hyperboloidal mirror. An unfortunate by-product of the grazing incidence is that the light rays converge only slowly and so the focal length is large, which is not very convenient in a spacecraft. At the present time, gold coated mirrors may be used to about 10 keV of X-ray energy. Much experimental work is currently being done in Japan and elsewhere to try to extend this to higher energies by employing multilayer coatings. It is expected that this may push up the limit to perhaps 50 keV. X- and gamma-ray detectors tend to be sensitive also to energetic particles around the earth or in the solar system. The larger the detector, the greater this problem. In the absence of focussing telescopes, large detectors have to be directly exposed to the sky to detect faint sources. So the source signal increases with the size of the detector, but so does the particle noise, reducing the sensitivity. But with imagers the situation is different: the X-ray collecting surface may be large, but the detector need not be bigger than one resolution element. Hence, the signal-to-noise ratio is much improved. NASA’s “Einstein” was the first satellite which made effective use of such X-ray optics. Also gamma-ray satellites appeared early on with NASA’s SAS-2 (with Italian participation) in 1972, which lasted only 8 months, too short to obtain sufficient statistics. Three years later followed Europe’s COS B5) which for seven years surveyed the sky. It mapped diffuse galactic radiation due to collisions of cosmic rays with interstellar gas and detected several dozens of discrete sources. While for more than a decade the COS B results remained unequalled, it was a small satellite and the angular resolution was no better than 5 degrees making convincing identifications with sources at other wavelengths difficult.

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The first ESA X-ray observatory was EXOSAT, launched in 19836). During its three year lifetime it obtained excellent observations which extended to higher energies than could be reached by “Einstein”. On board were a 1.5–50 keV hard X-ray detector and a telescope for the 0.04–2 kev imager/grating spectrograph. One of the original aims of EXOSAT had been to observe lunar occultations of X-ray sources and thereby to determine angular sizes. For this purpose it was placed in a very elongated orbit with an apogee of 192,000 km. Most of the time then would be spent far from the earth with a low speed with respect to the moon. With the better imaging capabilities of the “Einstein” (and in a more minor way EXOSAT) focussing optics, the occultation mode had become largely redundant. However, the high orbit meant that continuous observations of 72 hours duration were possible. This permitted the discovery of Quasi-Periodic Oscillations in the X-rays emitted by accreting neutron stars. These QPOs provide information on the interaction of the infalling matter with the magnetosphere of the neutron star and on the rotation of the latter. The Transmission Grating Spectrometer took only a few spectra because of a hardware problem, but these provided the data on which models of stellar coronae could be based. The long continuous observations also allowed the first detailed studies of stellar flares. An active visitor program contributed to the expansion of the X-ray community in Europe. Studies of quasars and galaxies took 31% of the observing time and black holes, neutron stars and other stellar sources 54%. While the next ESA mission for X-rays would not be launched before the end of 1999, two national initiatives, ROSAT and BeppoSAX, allowed the European astronomers to continue making substantial progress. First in 1990 came the German satellite ROSAT with focussing optics and high efficiency till about 2.4 keV in energy7). In the ROSAT all-sky survey some 100,000 sources were detected for the first time, more than half of them quasars and the remainder mainly stars, though also normal galaxies and clusters of galaxies were found. Included in the ROSAT payload were also a High Resolution Imager (HRI), provided by the US, and a grazing incidence Extreme UV telescope, contributed by the UK. With the latter an all sky EUV survey was made which detected more than 1000 sources in the range 60–200 Å (200–60 eV), mainly white dwarfs and active stars. Absorption by interstellar gas in our Galaxy is too strong to see much of the extragalactic Universe at those wavelengths. As a result of the ROSAT surveys the numbers of catalogued X-ray and EUV sources were both increased a hundredfold. In the “Lockman hole”, an area of low absorption, the HRI in observations totalling more than a million seconds was able to reach sufficiently low flux levels to show that at least 70–80% of the X-ray background observed in low resolution observations was resolved into individual sources, almost all quasars and Seyfert galaxies. For seven years ROSAT continued to generate data on hot stellar coronae, supernova remnants, neutron stars, clusters of galaxies and every

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variety of quasar or Seyfert galaxy. For many classes of objects inferences previously had been drawn from two or three examples. Thanks to ROSAT for the first time large statistical samples became available which provided a basis for reliable conclusions. As an example, before ROSAT only a few galactic star clusters had been observed. With the ROSAT sample of nearly 30 clusters, it could be clearly demonstrated how the stellar X-ray luminosity declines with age. Several pulsars were found to be pulsing X-ray sources, but also non-pulsing cooling neutron stars were identified. The latter provided constraints on the relation between pressure and density in matter at or above nuclear densities. Through an ample flow of postdocs at the Max-PlanckInstitut für Extraterrestrische Physik near München and through extensive collaborations with scientists elsewhere, ROSAT has much benefitted the whole European astronomical community. As ROSAT aged, the Italian Space Agency in 1996 launched its major X-ray satellite, BeppoSAX, with a set of instruments that could observe the whole range of X-ray energies from 0.1 to 100 keV8). After a difficult path towards realization it has been a brilliant success. The broad energy range has enabled us to obtain clear information on X-ray spectra and absorption in quasars and related objects, on the hard X-ray background and on a variety of problems involving neutron stars and black holes. Originally there had been two proposals in Italy: one to build an X-ray imager like the one on the “Einstein” satellite and one for what is now BeppoSAX. While SAX was chosen in 1982, the losing party both in Italy and in the US still tried to torpedo the project as late as two years before launch. Fortunately, both the Italian Space Agency and the Science Ministry were in the hands of scientists who understood the matter. Following a review by an eminent Italian scientist, the government asked the European Science Foundation to give an opinion. All of us in the advisory committee unanimously agreed that SAX should be continued. I have been amazed about the shortsightedness of the opponents: if they had succeeded to abort the project after much of the money had been spent, the credibility of the whole Italian astronomical community would have been lost. Now in collaboration with their Dutch partners, who provided two excellent wide angle X-ray cameras, they have collected one of the great prizes of the decade – the identification of the sources of the mysterious gamma-ray bursts and the determination of their locations in the furthest reaches of the Universe. Such bursts leave a faint X-ray and optical afterglow that rapidly weakens. With BeppoSAX it was possible to determine the position of the X-ray afterglow sufficiently fast and with adequate accuracy for the optical counterpart to be found, which turned out to be located at the edge of a galaxyy with a redshift of 0.7. Also stellar flares were detected and emission over the full 0.1–50 keV range was found, indicating that the flares were associated with gas at a temperature of 108 K. While BeppoSAX would last till 2002, the large ESA X-ray satellite XMM (first proposed to ESA in 1982 and now baptized XMM-Newton) began

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to provide data in early 20009). With three telescopes of 58 shells each of gold plated focussing optics (Figures XI, 8, 9) providing a high sensitivity and 4.2–6.6 (FWHM) arcsec angular resolution, its instruments (Table XI, 3)

Figure XI, 8. A mirror module for XMM-Newton. The 58 gold plated shells reflect incoming X-rays by double reflection.

Figure XI, 9. Artist impression of XMM-Newton in orbit. The three mirror modules are visible under the sunshade. The detectors are at the right at the foci of the modules. The focal length is about 7 m.

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cover the range of 0.1 to 10 keV at spectroscopic resolutions of up to 700 at some energies. XMM-Newton is particularly effective in the hard 5–10 keV band. BeppoSAX had pioneered the detection of sources in this energy range and resolved some 30% of the X-Ray Background. XMM reaches a factor of more than ten fainter at these energies, and now 60% of the XRB is resolved into individual sources. As yet there is no evidence of a truly diffuse XRB of cosmological origin. Of course, there is more to XMM than the XRB, but the variety of its programs precludes giving an account here (Figures XI, 10, 11). In addition to the X-ray imagers and spectrographs, XMM carries an optical/uv monitor. Also in 1999 NASA launched AXAF (now “Chandra”), an X-ray mission with focussing optics; its principal aim was to obtain the best possible angular

Figure XI, 10. The 30 Doradus region of the Large Magellanic Cloud seen by XMMNewton. Supernova shells and point like sources (mainly X-ray binaries) are seen. Harder X-rays are shown in blue and softer ones in red.

Figure XI, 11. Quasars and other extragalactic X-ray sources in the Lockman Hole where absorption by the interstellar gas in our Galaxy is particularly low. The red sources (with a white core if strong) emit mainly soft X-rays, the blue ones hard X-rays. Some of the spectra obtained by XMM-Newton are also shown. The second spectrum from below on the left is rather soft. Its counterpart on the right is much harder with only photons above 1.5 keV. Even though the latter’s flux is only just above 10–7 photons/(cm2 sec kev) at 8 keV an adequate spectrum could be obtained thanks to the large effective area of XMM. The two spectra at the top are very soft.

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resolution (§ 1 arcsec). For once this was a felicitous combination of competition and collaboration: AXAF would obtain the finest images, while XMM with its large collecting area would obtain the best spectra. In particular in fainter objects, the diagnostically important iron line at 6.4 keV is only accessible by XMM. The cost of XMM including instrumentation is somewhere around 900 M€ , while that of AXAF appears to have been substantially more. XMM is expected to remain operational for a decade. While the overall European program represents a coherent approach to X-ray astronomy, of course others have also launched missions10). At NASA, the Einstein satellite (1978) had been the first with focussing optics. The US also provided the High Resolution Imager for ROSAT. Subsequently RXTE (1995), the Rossi X-ray Timing Explorer, took over where EXOSAT had left off, with high time resolution for hard X-ray observations. Chandra preceded XMM-Newton by some months. In Japan the Institute of Space and Astronautical Science launched a series of highly successful X-ray satellites, Tenma (1983), Ginga (1987) and ASCA (1993), which were to be followed by the powerful Astro-E just after XMM-Newton. Unfortunately, it was destroyed in a launch failure; a follow up is now scheduled for 2005. All these satellites made important contributions to the field, in particular ASCA with its optics usable up to 10 keV which allowed it to observe hard X-rays from many galactic and extragalactic sources in which the softer X-rays are absorbed. All in all the contributions of the EU, the US and Japan have had a rough equivalence. Cooperation between the three has been satisfactory. A summary of the X-ray missions may be found in Table XI, 2. Also India has plans for a substantial X-ray/uv mission ASTROSAT to be launched in 2008. In addition to two 38 cm uv telescopes, it should have 0.6 m2 hard X-ray counters and also a 200 cm2 effective area soft X-ray telescope with UK participation. Various plans are being made for future X-ray missions beyond Newton-XMM, Chandra and ASTRO-E, but nothing appears to be firmly decided. XEUS, for X-rays from the Extreme Universe Spectroscopy, started out in Europe as a Space Station related project. The idea was to gradually build up large focussing optics, which subsequently would be brought to the Space Station for assembly into an X-ray facility of increasing size. Once a large enough area would have been assembled the facility would be set free, since the ISS is not very suitable for very precise pointing. Subsequently, as more optics arrived, it would be captured again, the new elements would be integrated into the facility, and it would again be set free, etc. At the time that the organizations responsible for the ISS were looking rather desperately for a purpose to justify their huge investment, this seemed promising. However, in the meantime the future of the Space Station has become much more uncertain as a subsequent industrial fantasy project happens to take its place. Moreover, the very low earth orbit would be quite inconvenient with earth occultations very much reducing efficiency. Thus, in the meantime XEUS has evolved into an autonomous facility at L2.

†

USA

Russia

Ginga

Tenma

ASTRO-E2

Asca

Japan

50 60 25 37 1000 100 30 GeV 200 400 10 MeV 150 50 GeV 300 GeV 1.3 MeV 30 MeV 400

0.16 0.10 0.17 0.40 0.20 0.25 0.15 0.78 0.01 0.55 0.52† 0.06 0.8 0.08 0.02

12

2 10 10/120 7 12

Emax keV

0.15

0.05 0.08 0.015/.05 0.08 0.40

Eff. Area m2

15 60 –

50 150 180 90 8 6 60 60 60 12 0.3† 30 20

1.5

0.07 1.5 1.6 0.01 0.09

Ang. Resol.

120 3000 10000

0.5 8 9 2 3 4 2000 1 5000 80 – 8000 6000

0.1

3 0.5 0.3 0.01 0.2

FOV

21

7 19 8 20 9

Notes

12 23 25

6 22 22 UK 22 D, NL, UK, ESA 22 F, Dk 22 D 23 24 F 25 Russ/I/F/Dk/ESP 14 I, UK 25 17 I, D, F, S, J 26

UK, D, NL, I

US

US, UK US NL NL, D UK, NL, D

Major contrib.

Effective area for γ-ray burst alert telescope, but angular resolution for 0.01 m2 X-ray tel; also copy of XMM-Newton optical monitor.

With focussing telescope 1990-98 ROSAT (D) 1993-01 1996-02 BeppoSAX (I) 1999Chandra XMM-Newton 1999(ESA) 2005 With collimators or coded masks 1983-86 EXOSAT (ESA) 1983-84 1983-88 Astron 1987-91 1987-01 Röntgen/Kvant 1989-99 Granat 1991-00 COMPTON 1995RXTE 2000HETE INTEGRAL (ESA) 20022004 SWIFT 2006 AGILE (I) 2008 GLAST Major European instruments on non-EU spacecraft 1989-99 SIGMA (F) on Russ GRANAT 1991-00 COMPTEL (D) on US COMPTON 2000FREGATE (F) on US HETE

EU

Table XI, 2. X- and γ-ray missions launched after 1980 by Europe, the US and Japan. The effective collecting areas (in m2), angular resolutions (in arcminutes) and fields of view (in square degrees) generally vary with energy, and therefore are only indicative. Representative values for the highest energy (in keV, unless stated otherwise) are given. More accurate descriptions may be found in the scientific literature. Several spacecraft also have γ-ray monitors on board which have not been taken into account in the table, unless indicated.

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There are four principal motivations for building XEUS11): the study of the hot gas in clusters of galaxies (with their large dark matter content) at moderate redshifts, the origin and evolution of black holes at large redshifts (z = 10?), the nature of space–time around black holes, and the nature of matter under extreme conditions, perhaps beyond those found in neutron stars. To explore those areas, angular resolutions down to a few arcsec, effective collecting areas of at least 10 m2 and time resolutions of μsec are required. Such a telescope will have a large focal length (50 m?). Since it is not feasible to have this in one structure with the mirrors, the detectors would be in a separate satellite. With the same ionic thrusters as used in SMART-1 (chapter XII), the mm accurate relative positioning of the two satellites should pose no insurmountable problems. The example of BeppoSAX has shown the importance of observing hard X-rays up to at least 50 keV. To obtain sufficient angular resolution and sensitivity, it would be desirable to utilize telescopes also at high energies. The hard X-ray reflectivity of the mirrors may be obtained with multilayer reflective coatings. Since the Japanese have also built up some experience with such mirrors and are considering a future hard X-ray telescope (NEXT), an ESA–ISAS partnership might be very fruitful. At NASA the preferred future project has been CONSTELLATION, an array of four X-ray telescopes on independent satellites which would all be pointed in the same direction. Current planning suggests a launch after 2016 at the earliest. In addition to these very large X-ray missions, several survey type instruments are planned which would be attached to the Space Station. These include ROSITA, a German-ESA cooperation for a sensitive hard X-ray survey (> 2 keV). It would in a way replace an earlier German mission ABRIXAS which failed in 1999 because of an error in the power system. ROSITA should detect some 50,000 sources. In addition, Lobster-ISS would be an ESA all sky monitor which would produce an X-ray catalog of 200,000 sources every two months so as to detect variable objects. Japan is in an advanced stage of building such an instrument with lower sensitivity. Finally, in the US EXIST is being planned for surveying the whole sky every 90 minutes in the 6–600 keV range. All these plans depend on the future of the Space Station. For ROSITA a free-flyer option is also being studied. Gamma-ray astronomy has its own particular problems. Of course, the boundary between X- and γ-rays is rather arbitrary with hard X-rays extending up to 50 keV or more. Since no focussing optics exist, γ-ray telescopes have generally made use of mechanical collimators which limit the angle from which rays may reach the detector. Not surprisingly the angular resolution is poor. More recently coded masks have been developed. A coded mask in front of a detector hides selected parts of the field. Pointing the telescope in slightly different directions, different areas of the sky are occulted and a comparison of the results yields the location of the sources. The application of this technology to the French SIGMA instrument on board of the Russian GRANAT mission has been particularly successful12).

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Without focussing optics the detector has to be large and the background due to charged particles hitting it is high, especially in the energy range around an MeV. Hence also the sensitivity is relatively low. The situation improves at much higher energies where the tracks of individual photons can be followed in spark chambers and other detectors familiar to particle physicists. So the direction of the origin of the γ-rays can be determined and background events become less important. In 1972 NASA launched the SAS-2 satellite which during its seven months lifetime detected high energy emission from some pulsars, but which accumulated insufficient statistics on most other sources. With COS B (1975–82) ESA made a first partial sky survey in the 0.03–5 GeV energy range which yielded more than a dozen sources. In addition, it mapped the diffuse γ-ray emission from the galactic plane which results from unresolved sources, from cosmic-rays colliding with nuclei in interstellar matter and from energetic electrons. In the meantime, American satellites which had been launched to verify that the nuclear weapons test ban treaty was obeyed, had discovered Gamma Ray Bursts, short spiky flashes of γ-rays with overall duration of seconds or less. Gamma-ray astronomy got a major boost from the launch of the NASA Compton Gamma Ray Observatory, a decade long mission launched in 1991. It contained instruments for the study of high energy γ-rays, Gamma Ray Bursts, hard X-rays, and also a German instrument COMPTEL (with NL, US and ESA contributions) intended for the difficult 1–30 MeV range. Among the results from COMPTEL is the discovery of emission at 1.16 MeV from radioactive titanium (44Ti) in the supernova remnant Cas A which probably exploded in 166713). With a half life of only 78 years it was clear that it must have been synthesized very recently in the supernova event. Later the result was confirmed by BeppoSAX from other lines. Already in 1985 a proposal had been made for a new ESA γ-ray mission (GRASP), but it had not been selected in the competition. Since usually several missions compete for one slot in the program, and since a balance has to be maintained between the different disciplines, this in no way indicated lack of merit. Subsequently, a new proposal was made for a very similar project, and this led to INTEGRAL, the INTErnational Gamma-Ray Astrophysics Laboratory. INTEGRAL is an ESA mission with a large Russian participation14). It was launched in 2002 with a Russian Proton rocket into a high orbit with apogee at 153,000 km well beyond the earth’s radiation belts (Figure XI, 12). The two principal instruments (Table XI, 3) for the 15 keV–10 MeV range are a coded mask imager with 12 arcmin angular resolution and a spectrometer with a spectral resolution of 500–1000. These are supplemented by a 3–35 keV X-ray instrument and an optical monitor to ensure that the highly variable γ-ray sources can be observed over a wide range of photon energies. The γ-ray spectrometer is expected to detect a number of radioactive elements in the interstellar medium that have been

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Figure XI, 12. The γ-ray observatory INTEGRAL. Four instruments are on board which are identified in Table XI, 3; the IBIS coded mask in the back with its detector below, next to it the two coded masks of JEM-X, and below the detectors just visible behind the round tube of SPI. Right next to the JEM-X masks is the OMC. The solar panels are 16 m across; the mass of the satellite is 4 tons, with the instruments accounting for half of the total.

synthesized during the last 100 to 1,000,000 years in supernova explosions and Wolf-Rayet stars. Early results from INTEGRAL include the resolution of the γ-ray emission around the Galactic center into several dozens of sources (Figure XI, 13) and the discovery of some very heavily absorbed objects. A number of Gamma-Ray Bursts were detected. GRB are brief (msec–sec), extremely energetic events, possibly associated with stellar interiors collapsing into black holes during supernova events. They frequently leave afterglows also at visible wavelengths from which a more precise location may be obtained. Since these afterglows are also very short lived, a small telescope is needed that can quickly point to the area where the γ-ray source was

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Table XI, 3. The instruments on XMM-Newton and INTEGRAL. From left to right the columns give the PI country, the energy range in keV, the energy resolution, the effective area in cm2, the angular resolution in arcminutes and the field of view in square degrees; E/ΔE, Aeff and angular resolution may be energy dependent, in which case a representative average has been taken.

Acronym PI UK1)

E (keV)

E/¨E

Aeff 4000 100 700

EPIC RGS OM

NL UK

0.25–12 0.35–2.4 visible/uv

100 400

IBIS SPI JEM-X OMC

I F Dk Esp

15–10000 20 - 8000 3–35 visible

10 600 8

1) Initially Italy. “instrument”.

2)

6000 500 1000 20

Ang. Res.

FOV

0.09

0.20

0.03

0.06

12 120 3 0.3

80 250 23 20

XMM ↑ ↓ INTEGRAL2)

The Integral Science Data Centre (CH) was also considered an

Figure XI, 13. INTEGRAL resolved the γ-ray sources near the center of our Galaxy. The image covers 30° in longitude.

detected. Two robotic telescopes have been placed at La Silla, the very fast (seconds) 25-cm TAROT15) (F) for observations in the visible and RME16) (I) with a slightly slower 60-cm telescope which also accesses the near IR. As soon as INTEGRAL or the NASA satellite SWIFT, which is more specifically optimized for detecting GRBs, observes an event, the corresponding information is fed into the worldwide network and these telescopes (and others

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elsewhere) automatically move to the right position. Such small telescopes can only track the initial very luminous phase, but thereafter the VLT can take over. A small gamma-ray observatory at higher energies (30 MeV–50 GeV) is being developed by the Italian Space Agency for launch in 2006. This mission “Astro-rivelatore Gamma a Immagine LEggero” (AGILE) should image about 20% of the sky simultaneously at 30 arcminute (at 1 GeV) resolution17). Because of its efficient silicon detectors AGILE will have a mass of only 60 kg–30 times smaller than the corresponding instrument (EGRET) on the NASA Compton Observatory which was based on more classical spark chambers. As a result the cost will also be much lower, with a target cost of 40 M€. Even if this aim could not be quite realized, the cost reduction would remain quite spectacular. Around 2008 AGILE will be followed by the big NASA mission GLAST, with 20 times better sensitivity. However, AGILE remains very useful, because high energy gamma-ray sources tend to be variable and continuity in the observational record is important. Several European laboratories are participating in the GLAST instruments. In Table XI, 2 a semiquantitative comparison is made between the W. European, American, Russian and Japanese X- and γ-ray missions. Of course, the description is very incomplete, since the parameters for different instruments and energies may be very different. Nevertheless, it is clear that a rough equality prevails between the four. It is also clear that for this to remain the case, a major effort will be needed in Europe to secure funding for at least one future mission. The European X-ray community has survived the 13 year gap in ESA X-ray missions thanks to the German and Italian satellites and by participation in non-European missions. However, after 2005 no major project appears to be in the pipeline, either from ESA or nationally, and so the future of an independent European X-ray astronomy is contingent on the early realization of XEUS.

Ultrahigh Energy Gamma-Rays The GLAST mission will detect γ-rays up to about 300 GeV. However, even from the stronger sources few photons will be detected. At such energies the fluxes are so small that affordable detectors have inadequate collecting areas to obtain meaningful statistics. Since the spectra are very steep, at still higher energies no detections can be expected. But the most energetic photons are particularly interesting since they convey information about the extreme events in the Universe. Fortunately, other techniques are available to detect such high energy γ-rays. When such a γ-ray photon hits the earth’s atmosphere, it initiates a shower of electrons and positrons. Since these are highly relativistic, they will emit Cerenkov radiation at visible wavelengths in the form of nanosecond

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duration flashes. These may be observed by large telescopes of very modest optical quality and, therefore, of modest cost. The larger the telescopes, the lower the energy that still can be detected. In practice, such telescopes are made of a large number of glass segments mounted in a rather simple metal frame. Following the first 10-m Whipple telescope in Arizona, a number of experiments have been made to utilize the large collecting areas of solar power plants. These included CELESTE, at a defunct solar plant in the French Pyrenées with 2000 m2 collecting area, GRAAL, a German-Spanish experiment, and STACEE in the US. Because of their large areas, CELESTE and STACEE were able to detect photons with energies as low as 50 GeV. The solar plants have large collecting areas, but they are far from optimized for suppressing the strong background from cosmic-rays and to obtain precise positions. This is best achieved by stereoscopic observations with several dedicated telescopes. A first such array, HEGRA, was built by the MaxPlanck-Institut für Kernphysik in Heidelberg and placed at La Palma. It consisted of six telescopes with the rather small area of 8.5 m2 each. This cooperative venture of D, ESP, Armenia was in operation from 1997–2002. Other relatively small arrays were built by France, the UK and others. The first source of TeV γ-rays to be detected was the Crab Nebula. It is a strong source of visible radiation and of X-rays. Both are synchrotron radiation due to energetic electrons gyrating in the nebular magnetic field. So we gain information on the combination of these, but not on each separately. The magnetic field could be weak and then there would have to be many electrons to produce the observed radiation, or it could be strong and fewer electrons would be needed. Some of the synchrotron radiation may scatter against the energetic electrons, and the resulting Compton radiation would have energies in the GeV and TeV range. The observation of these high energy γ-rays allows the number of electrons to be determined, and we then can also determine the strength of the magnetic field. A few very active galactic nuclei (AGN) have also been detected, with photon energies as high as 20 TeV, probably also due to the Compton effect. At such high energies these photons may be destroyed by scattering against the photons of the Cosmic Microwave Background. Some evidence has been found that this depletes the spectrum at the high energy end. If this were not the case, these events could not originate from photons, but have another unknown origin. Because of the many ramifications of the detection of high energy γ-rays, new larger telescopes and telescope arrays have been built or are being constructed. The four most important ones are listed in Table XI, 418). The stereoscopic observations of HESS have particularly good angular resolution, while MAGIC (Figure VI, 2) is able to observe γ-rays down to perhaps 20 GeV because of its large collecting area. The costs are still very manageable. The 17-m MAGIC telescope is said to have cost about 4.5 M€,

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Table XI, 4. The four principal instruments for detecting TeV γ-rays. Several of these instruments may be further expanded in the future.

Name

Size

Year

Participants

Hemisphere

HESS MAGIC CANGAROO III VERITAS

4 × 107 m2 1 × 234 m2 4 × 57 m2 4 × 100 m2

2004 2003 2003 2006

D, F, UK ... D + 9 others J, Australia US, Ei, UK

S N S N

while the complete future VERITAS project of seven 12-m telescopes has been budgeted at 35 MUS$ (2000). It has been delayed by the usual ecolo-religious site problems in the US, and will first be built with four telescopes. A second MAGIC is also likely to be implemented, and other telescopes may well follow in the various projects. So the first half dozen sources detected with the instruments of the first generation should be joined by many others during the coming few years. At present, there are still important disagreements between observations of some sources by different instruments. While variability plays a role in this, it also shows that it is not a superfluous luxury to have two main instruments in each hemisphere. With positional accuracies of typically ten arcminutes or less, reliable identifications with known visible objects should be obtainable for many sources.

XII. European Space Missions: The Solar System

…that there is at long intervals a variation in the course of the heavenly bodies and a consequent widespread destruction by fire of things on the earth. Plato1)

The solar system consists of the Sun, the planets and their satellites, the asteroids – small rocky bodies and the icy bodies mainly in the cold outer reaches. The Sun and the heliosphere, the gas, magnetic fields and energetic particles flowing outwards through interplanetary space will be discussed in chapter XIII. The terrestrial planets (or inner planets) Mercury, Venus, Earth and Mars are solid bodies, with in the case of Earth and Venus substantial atmospheres. Their masses range from 0.82 earth’s masses for Venus to 0.11 and 0.06 for Mars and Mercury respectively. Surface gravities in the same order amount to 0.88, 0.38, 0.37 times that on earth. The outer planets Jupiter, Saturn, Uranus and Neptune are much more massive (318, 95, 15 and 17 earth’s masses respectively) and are largely gaseous though they should have rocky cores. The Moon has a mass 81 times smaller than Earth. Other satellites with a comparable mass are the four Galilean moons of Jupiter and Saturn’s satellite Titan. Numerous more negligible satellites exist. The four inner planets have distances of 0.39, 0.72, 1.00 and 1.52 AU (astronomical units), while Jupiter and Saturn are at 5.20 respectively 9.54 AU. The asteroids are found mainly between Mars and Jupiter, but some come close to Earth and on rare occasions collide with it. The most massive asteroid is Ceres with a mass some 70 times smaller than the Moon and the next one is already a factor of four less than that. The solar system was formed by the coalescence of many smaller “planetesimals” that had originated in contracting dense clouds of interstellar gas and dust. At the same time the Sun was beginning to radiate.

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At small distances the volatile parts of the planetesimals evaporated and the rocky planets from Mercury to Mars ultimately resulted. Further out the more massive planets Jupiter to Neptune formed, which were able to also retain much of the gaseous matter. Far out the Sun’s radiation was too weak to evaporate the icy aggregates, and after the planets had formed their numbers were too small and their motions too fast to form larger units by sticking together. Thus, many of them have stayed unchanged in the outer reaches of the solar system.

Comets Gravitational effects of the planets or of passing stars occasionally perturb the orbits of the remaining planetesimals and may place them on trajectories that pass closer to the Sun. Rapid evaporation follows. The solar light will be reflected by the escaping dust particles or excite the gas that subsequently reradiates the energy. The solar wind and radiation pressure interact with this matter and stretch it into a long tail in the antisolar direction: a comet is born. Analysis of cometary tails by earth bound telescopes gives some information about the composition of the comet, but only with spacecraft which approach much more closely are we able to see the nucleus in a less processed state. The first European venture into the wider solar system was the Giotto mission to comet Halley, which comes close to the Sun once every 76 years. Launched in 1985, the Giotto spacecraft arrived close to the comet in the following year passing its nucleus at a distance of only 596 km. As a result, for the first time detailed images of a cometary nucleus were obtained (Figure XII, 1)2). The surface turned out to be surprisingly black with some bright spots. Jets of escaping dust and gas emerged from some localized areas facing the Sun, but most of the surface was inactive. Prior to Giotto it was thought that a comet was a “dirty snowball” composed of ices with a relatively small amount of dust. Actually, there was found to be as much dust as ice, and the basic structure of the nucleus may well be determined by fluffy dust aggregates which originally condensed in interstellar space. The evaporating ice drags along some of the dust. Water vapor was found to be the dominant constituent of the gas, but CO, CO2, CH3OH, NH3 (ammonia) and minor amounts of other substances are also observed. These findings are important for studies on the formation of the solar system which may have resulted in part from the aggregation of many planetesimals of which the cometary nuclei are the last survivors. Several other missions passed the comet at much larger distances: two USSR Vega spacecraft at 10,000 km and two Japanese spacecraft at 100,000 and 8,000,000 km respectively. The US International Comet Explorer (formerly ISEE-3) observed the comet from 30 million km after having passed by the Giacobini Zinner comet at 7800 km

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Figure XII, 1. The Giotto image of the nucleus of comet Halley at resolutions ranging from 100 m to 800 m. The scale is 2.2 km/cm. The nucleus is very dark except in places where the Sun creates hot spots from where jets of dust and gas are ejected in the solar direction. Ultimately, radiation pressure and the solar wind will deflect this matter to form a tail in the antisolar direction.

from the nucleus. So only Giotto had the resolution needed to study a cometary nucleus. Following its passage by comet Halley, the spacecraft was directed towards comet Grigg-Skjellerup where it arrived four years later. The imaging camera had been destroyed by the dust particles from Halley, but useful data were obtained on the interaction of Grigg-Skjellerup with the solar wind. While the results of Giotto clarified some aspects of cometary nuclei, much remains unclear because the observations were still obtained at quite a distance. To make further progress in situ study of the nucleus would be needed. In 1984 the Horizon 2000 program already included a major mission to do this and to perhaps return a sample to earth. From 1986 it was studied jointly as a collaborative project with NASA, but by the end of 1991 it became clear that the implementation schedules of the two agencies did not match

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and NASA withdrew. It then appeared that the sample return would be beyond ESA’s financial means. The in situ part of the mission remained and became “Rosetta” consisting of an orbiter and two landers. One of these would be provided by a CNES-NASA collaboration. However, in 1996 NASA also pulled out of the lander for “budgetary and programmatic reasons”3). The two landers then became one all European lander. The orbiter will first map the nucleus from distances of the order of 100 km and subsequently descend to a few km for detailed studies. Because of the low gravity orbital velocities are of the order of only one m/s, which makes the orbital manœuvers quite delicate. After selection of a suitable location the lander will be released and placed on the surface. The orbiter has instruments to make multicolor maps, more detailed spectroscopy of the surface, to study the composition (including some isotope ratios) of the gas and dust escaping from the nucleus and to measure magnetic fields, etc. With the lander detailed imaging and analysis will be made of the surface materials, while also some subsurface measurements and deeper soundings will be performed. Initally Rosetta4) was scheduled for launch in January 2003 with the target being comet Wirtanen. However, the failure of a modified Ariane 5 rocket in December 2002 made it seem imprudent to go ahead before the circumstances of this event had been clarified. Since the spacecraft would need gravity assists from several planets, the original orbit could no longer be implemented. Finally, it was decided to choose comet ChuryumovGerasimenko which, in fact, had earlier been the preferred target, albeit for a mission one orbital period earlier. Rosetta was successfully launched in February 2004. This comet is particularly attractive since it has spent only a small number of orbits close to the Sun (until 1840 perihelion was at 4 AU ; encounters with Jupiter reduced this to 1.3 AU), and so it may be in a relatively pristine state, less changed from the days when the solar system formed than the more typical short period comets. Observations with HST and VLT have been made. The nucleus has a size of 3 × 5 km and a rotation period of 12 hours. So it is three times larger than comet Wirtanen. As a result, the gravity is likely to be stronger which necessitated changes in the landing gear. The rendez-vous of Rosetta with the comet is foreseen for May 2014, when it is still at four astronomical units from the Sun. The orbiter will continue to orbit the nucleus as it becomes more active due to its approach towards the Sun, while the lander should be placed on its surface in November 2014 (Figure XII, 2). The mission will come to an end in December 2015, four months after perihelion passage. From mission conception to conclusion about 30 years will have elapsed. It will have taken some 16 years between the beginning of instrument construction and first data. Such long times cause difficulties: some of the investigators will have retired or developed other interests, while it is not easy in a university environment to engage doctoral students for such a long range project.

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Figure XII, 2. Artist’s impression of the Rosetta lander on comet ChuryumovGerasimenko. The surface is unlikely to be very smooth, and so the actual landing is a delicate, uncertain operation; it takes nearly an hour between the time the lander is observed and the arrival of a follow-up command from earth.

Cometary landers should be prepared for surprises. Comet SchwassmannWachmann 3 had been considered as a back-up in case there were problems with comet Wirtanen. A few years later during perihelion passage it broke up into three pieces. Even more spectacular was the demise of comet LINEAR5). It was discovered in late September 1999. Its orbit showed that it came from the Oort cloud of comets in the outermost reaches of the solar system. On passing perihelion ten months later it broke up completely. An image taken with the VLT 11 days later shows 16 fragments (Figure XII, 3) which a week later had become invisible. The Rosetta comet which has been much longer relatively near to the Sun is very unlikely to undergo such an extreme event. However, the splitting of cometary nuclei is not exceptional. Cometary projects elsewhere include in the US the “Stardust” mission (1999) which is to collect dust from the coma of comet Wild-2 and bring it back to earth in 2005, and in 2001 flybys of two other comets. The CONTOUR

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Figure XII, 3. The breakup of comet LINEAR in 2000 imaged by the ESO VLT with FORS I. The 16 fragements apparently originated some 11 days prior to this image and had vanished from view a week later.

mission aimed at flybys of three comets failed when the spacecraft was destroyed. In 2005 “Deep Impact” will send an impactor to the nucleus of comet Temple 1 and observe the result. The Rosetta spacecraft will pass by two asteroids and observe their surface. Also some US missions are aiming to observe asteroids.

Exploration of Planets and Satellites A major NASA mission (with ESA and Italy participating) to Saturn, “Cassini”, was launched in 19976). Attached to it was the ESA provided “Huygens” lander which late November 2004 arrived at Titan and two months later descended through the atmosphere. Titan is by far the largest satellite of Saturn with a mass twice that of the moon. From what is known the atmosphere of Titan is mainly composed of nitrogen with some methane and hydrogen at a surface pressure at about 1.5 atmospheres. These characteristics are thought to be not very different from those on earth around 4000 millions years ago before life had oxygenized the atmosphere. Nevertheless, the similarity is limited in that the temperature is much lower on Titan. There is some evidence that at the surface there are some lakes or oceans which could be composed of liquid methane. In about 2 hours Huygens traversed the Titan atmosphere from 100 km down to the surface, while being slowed down by

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a parachute. During this time, its six instruments measured temperature, density, composition, winds and aerosols in the atmosphere, studied clouds and imaged the surface. The spacecraft survived the descent and conditions at the landing spot could be determined. Because the light travel time between earth and Titan is more than 70 minutes, the whole Huygens descent had to be preprogrammed. The instruments on Huygens are listed in Table XII, 1. Of the 13 instruments on the Saturn orbiter two were European – a magnetometer (UK) and a dust analyzer (D). Early results from Huygens include the discovery of river-like surface features and some impact craters. The atmosphere contains nitrogen and methane. The lander appears to have penetrated one or two decimeters into the soil and its heat has evaporated some of the liquid methane in the surface layer. The first independent European planetary mission is “Mars Express” launched in 2003. While in the case of Huygens some of the conditions to be encountered were uncertain, much of what “Mars Express” would experience was well known. Numerous spacecraft have been sent to Mars: 18 by the Table XII, 1. Instruments on current ESA planetary missions.

ASPERA HSRC MARS MARSIS OMEGA PFS SPICAM

Mars Express Energetic Neutral Atoms High-Resolution Stereo Colour Imager Radio Science Experiment Subsurface – Sounding Radar IR Mineralogical Mapping Spectrometer Atmospheric High Resolution Spectrometer uv/IR Atmospheric Spectrometer

(S) (D) (D) (I, US) (F) (I) (F)

ASPERA MAG PFS SPICAV VERA VIRTIS VMC

Venus Express Energetic Neutral Atoms Magnetometer Atmospheric High Resolution Spectrometer uv/IR Atmospheric Spectrometer for Occultations Radio Occultation Instrument uv – IR Imaging and Spectrometer Wide Angle Monitoring Camera

(S, F) (A) (I) (F, B, Rus) (D) (F, I) (D)

Huygens ACP DISR DWE GCMS HASI SSP

Aerosol Collector Imager/Spectral Radiometer Wind Profile Measurement Atmospheric Composition Atmospheric Structure Surface Science Package

(F) (US) (D) (US) (F) (UK)

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USSR/Russia with modest success, 16 by the US with four failures, and one each by Europe and Japan, the latter also a failure. While earlier missions have given a general picture of the nature of the Martian surface and atmosphere, many of the essential questions remain unanswered. The main impression is that of an utterly dry planet, variably covered with impact craters. Since impacts were more frequent in the past, the density of such craters allows rough chronologies for different areas to be established. The most notable dichotomy with the northern hemisphere several km lower than the southern is not understood. The highly cratered terrain in the south must be very old. Elsewhere plains alternate with mountains and a few huge volcanoes. Olympus Mons (Figure XII, 4) rises 24 km above its surroundings, making it the highest volcano in the solar system. At its base this shield volcano measures more than 500 km in diameter. The relatively low density of impact craters on its surface suggests that volcanic activity has continued until relatively recently, if not until today. Some of the plains are so smooth that they have been taken to be the floors of ancient oceans or lakes. Elsewhere very eroded mesas are found (Figure XII, 5).

Figure XII, 4. Olympus Mons as imaged by the Mars Express stereoscopic imager. The huge caldera of 60 × 90 km is the result of an eruption in the highest volcano in the Solar System. The volcano rises 24 km above its surroundings – three times as much as Mauna Kea above the floor of the Pacific. Some impact craters from a later date are also visible. There is evidence for more modest volcanism in recent times. The scale is 1 cm/10 km.

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Figure XII, 5. Mesas on Mars. Erosion seems to have removed much of the surroundings of the 3 km high plateau area. The scale is 1 cm/2.5 km.

Fluvial morphologies in hilly terrain have suggested to most investigators that water was once flowing there above or possibly below the surface. At present there is very little water vapor in the tenuous atmosphere, which has a pressure of 6 millibar, only 0.6% of that on earth. Also some water ice is present in the polar caps which sublimates and freezes according to the seasons. The fundamental question about Mars is: where is the water now that appears to have been there in the distant past? Either it has gone underground to form a layer of permafrost or it has escaped into space. The issue is of vital importance if future manned missions are planned or if terraforming, the transformation of Mars into a more hospitable planet, is considered. Without water Mars will be forever dead. The question of water is also directly related to the question of life on the planet. Unfortunately, the issues of water and life are of such passionate interest to scientists, their funding agencies and the general public, that the standards of proof appear to have been relaxed sometimes in the rush to the next press release. Even though the atmosphere of Mars is very tenuous, like Earth it presents a global circulation. Its composition contains clues about the planet’s past, and some trace gases may provide evidence about current volcanism or biological processes. Planet wide sandstorms which may alter surface features and other meteorological phenomena are of much interest to the comparative climatologist. The climate history of Mars has been very complex because of the chaotic character of its orbital characteristics. Even over the last 10 million years its obliquity (the angle between the equatorial and ecliptic planes) has changed over the range 15–45°, while the eccentricity of

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its orbit has varied between 0 and 0.12. The much smaller variations of the orbit of the earth have been responsible for the modulation of the climate with glacial and interglacial periods. So much of the ice in the surface layers of Mars may have moved between different areas7). A first proposal for a European Mars mission, “Kepler”, was made to ESA in 1980. It was to be a relatively simple orbiter. In 1985 it was concluded that it would be advantageous to link it with a NASA mission that later became “Mars Observer”. The two parts of Mars Dual Orbiter would be independent, but coordination would increase the scientific value of both. However, in the meantime Cassini-Huygens had also appeared on the scene, which had been selected as M-1 in the new Horizon 2000 program. Mars Observer was actually launched in 1992, but failed. In 1989 a more ambitious Mars mission was proposed. By 1992 a phase A study had been completed by ESA of “Mars Net”, to be conducted jointly with NASA. It consisted of 3 landers. In parallel NASA had studied the Mars Environmental SURvey mission, MESUR, for 18 small landers. As Fred W. Taylor has written8): “One mission priced itself out of the market, while at the same time making the affordable mission look inadequate.” Subsequently, a somewhat changed version “Intermarsnet” was studied again, with the aim of a joint mission. It lost out in the ESA M-3 selection where Planck won. Intermarsnet would have consisted of three NASA landers and a European orbiter all launched together with an Ariane-5 rocket. At the time it seemed to me that NASA would have had the more interesting part of the deal. In the meantime European Mars enthusiasts participated in building instruments for the Russian Mars 96 mission which failed. After its failure into the Pacific, spares of the instruments were still available. It would be a waste not to use these. Combined with the strong emphasis in Horizon 2000 Plus on the scientific value of Mars exploration, this led to Mars Express. It was inserted into the program without the usual lengthy selection procedures. It was approved at 150 M€, not including the instruments. The UK added a lander to the instrument package. Substantial cost overruns, owing to rosy predictions of money flowing in from the general public, finally forced ESA to put another 16 M€ into the “Beagle-2” lander with subsequent arguments about the status of this “loan”. The story is an interesting appendix to the perpetual complaints of the UK delegation during the nineties about the perceived inefficiency of the ESA science program. Of course, it is also true that they were not the only ones to expect Europe to pay for their own programs. Mars Express consisted of an orbiter and a small lander9). The orbiter has a highly elliptical nearly polar orbit with perimars at 250 km altitude. Aerobraking made the orbit gradually more circular. A stereo imager is mapping the surface with 12-m resolution. Small areas are even imaged with a resolution of 2–3 m. Spectacular Stereoscopie images have already been

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obtained (Figures XII, 4, 5). With such high resolutions even small impact craters may be found which is helpful in dating different areas. The results document volcanic activity in the area of Olympus Mons as recently as a few million years ago10). Exciting evidence has been found for a frozen sea near the equator which would be as large as the North Sea11). However, on the other side of the Atlantic it is believed to be a lava flow12). The mapping IR spectrometer OMEGA for mineralogical studies with resolution of 100 m has made maps of the distribution of water ice and CO2 ice in the south polar cap. Widespread deposits of sedimentary sulfates, like gypsum, have been found. At the time of their formation water must have been present13). Spectrometers have analyzed the distribution of various gases and confirmed the presence of methane. Since methane would be destroyed relatively rapidly in the Martian atmosphere, a continuing production possibly indicates volcanic or biological processes. However, abiogenic pathways for methane production also exist. The interaction of the solar wind with the Martian atmosphere is being studied by an energetic neutral particle analyzer, while the surface roughness is studied by the reflection of radio waves. Of particular interest is the subsurface sounding radar which should determine mantle structure and water content down to the level where permafrost occurs. The unfolding of the radar antenna is a delicate matter and has been postponed to late in the mission, so as not to endanger the functioning of the other instruments. The instruments on Mars Express are listed in Table XII, 1. The lander Beagle-2, provided by the UK, was to study the landing site geologically and chemically, act as a weather station and search for evidence of life – present or past. Of particular importance would have been its ability to sample the subsurface soil which has not been modified by solar radiation and to determine the isotope ratio 12C to 13C which on earth is a sensitive indicator of biological processes. X- and γ-ray spectrometers would have allowed mineralogical studies and the determination of ages of the rocks found. Unfortunately, the lander was never heard of again after it had separated from the orbiter. Its remarkably low cost may have been too extreme. Nevertheless, the technological experience in miniaturization remains valuable for the future. For example, the whole X-ray spectrometer weighed no more than 300 grams. In parallel with Mars Express currently two NASA orbiters and two rovers are active on Mars. The surface is being mapped with resolutions comparable to those of Mars Express. A γ-ray spectrometer studies water ice buried near the polar caps. In 2005 an additional orbiter will be launched to map numerous places at sub-meter resolution and to look for evidence for water or ice; like Mars Express it will also carry a subsurface sounding radar. Other missions are planned by NASA every two years, with a sample return mission during the next decade.

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The future of ESA’s Mars missions is contingent on the funding for the Aurora program (chapter X). The program foresees an Exo Mars mission in 2011 with an orbiter and a rover equipped with a drill which will analyze the Martian soil and look for evidence of life. In addition, various technologies required for future exploration will be tested. A later mission in the Aurora program should include the return of a 500 gram sample for analysis on earth. At the moment the main contributors to Aurora are Italy and the UK. F, B, ESP, NL, A, P, S, CH and Canada also participate. After an initial refusal Germany now also has joined. The total envelope of about 42 M€ allows some industrial studies to be made. A substantially increased envelope will have to be decided at the next Ministerial Council meeting at the end of 2005, if the 2011 mission is not to be delayed. The relatively cheap spacecraft for Mars Express would be even cheaper if a copy were made. This has led ESA to plan a second mission, Venus Express, for launch at the end of 2005. Though some 23 (6 failures) missions to Venus have been launched by the USSR and 6 by NASA, basic questions about the planet remain unanswered. From the absence of old impact craters revealed by radar mapping and the uniform distribution of the younger ones, it has been concluded that the surface of the whole planet has been changed in a relatively short period some 500 million years ago. Perhaps the heat flow from the interior was higher than could be transported outwards through the very dry crust. This may have resulted in a global melting event. Other possibilities have also been considered. The CO2 rich atmosphere with its clouds of sulphuric acid accounts for the enormous greenhouse effect with the temperature at the surface above 300 °C. Trace gases about which not much is known must also contribute. A high altitude haze hides the surface from view, though some IR windows may allow direct observation of the surface. The nature of the haze and the chemical processes in the atmosphere remain to be elucidated, with volcanism undoubtedly playing a major role. Zonal winds at speeds of several hundreds of km/hour have remained mysterious. From the decision to build Venus Express to the launch date late in 2005, only three years will have elapsed. A much longer delay would have reduced the benefits of the commonality with the Mars Express spacecraft. Insufficient time and funding were available to build a complete set of new instruments. So most are derived from flight spares of instruments on Rosetta and on Mars Express. Included are a sounding radar for (sub)surface and ionospheric studies, uv–IR imagers and spectrographs, instruments for studying the atmosphere by observing occultations of the Sun, bright stars and radio sources, and plasma and particle analyzers for in situ observations. Instruments (listed in Table XII, 1) and spacecraft had to be adapted to the rigorous conditions around the planet. It is interesting that Venus Express could be decided and realized so quickly. Dedicated Venus missions had figured in Horizon 2000 with one proposal and in Horizon 2000 Plus with none at all, except for a remark that an international Venus mission could

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be of interest. Perhaps the history of Mars- and Venus Express shows that a more rapid turnover in the planning cycles of ESA would be advantageous. The SMART missions (Small Missions for Advanced Research in Technology) have been introduced into the ESA science program in the midnineties, as technology demonstrators. Very large missions could hardly take the risk to utilize untested technology. A cost cap of some 40 M€ was assumed, but SMART-1 actually cost 86 M€. While technology was the primary driver, some small scientific instruments could also be included, adding to the opportunities for a scientific community that was much concerned about the long waiting times between the larger missions. SMART-1, a lunar mission, was designed to test solar electrical propulsion, in which the energy collected by solar cells is used to create a jet of high speed ions14). So a small mass of a suitable material (in this case Xenon) produces a much larger thrust than would be possible with conventional rocket fuels. In principle, the same technology could be used when the power is derived from nuclear energy, which would make it possible to move into the farther reaches of the solar system where the solar energy flux is too small. However, at least in Europe, this could be expected to raise political problems. SMART-1 was launched in September 2003 into a Geostationary Transfer Orbit as a piggyback passenger on an Ariane 5 launch. Subsequently, its solar engine slowly let it spiral outwards, until it transferred into a lunar orbit. With the engine now thrusting in the opposite direction, it spiraled inwards towards an elliptical orbit with perilune at around 500 km above the surface. Because of the modest power (2 kW) available from 10 m2 of solar cells, the trip took about 15 months. On board of the spacecraft are a camera for imaging in four wavelength bands, a spectrometer for near IR mineralogical studies, and an X-ray spectrometer which will allow the elemental composition of the surface to be mapped by observing fluorescent X-rays. The three instruments have been successfully miniaturized with a total weight of less than 7 kg and a power consumption of only 25 Watt. Other instruments on board serve to monitor the propulsion system. Lunar missions have become quite popular again. Japan is planning a substantial orbiter for 2006, while India, China, and NASA intend to launch orbiters soon thereafter. ESA may participate in the Indian mission. The final element in the ESA planning for planetary research is the Mercury mission “BepiColombo”, which now is a cooperative venture with the Japanese Space Agency, JAXA. It is composed of two independent spacecraft to be launched by Soyuz-Fregat launchers in the 2010–2012 time frame. The direct path to Mercury would not be very long, but demanding on the launcher. So the gravitational assists of two flybys by Venus and two by Mercury will be used, supplemented by a solar electrical propulsion system. This trajectory will take some three years with the spacecraft arriving at Mercury not far from the time that Rosetta reaches its destination.

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The ESA component of the mission, the planetary orbiter, will observe the surface of the planet from the height of 400 km and more. The JAXA Magnetospheric Orbiter will be a spinning satellite in an orbit with an apoMercury of some six planetary radii. The interest of Mercury to the planetary community is twofold. The mean density of the planet is 5.4 g/cm3, which indicates that it must have a large iron-nickel core with a radius 3/4 that of the planet. The planetary or cometary bodies in the solar system range from H2O icy and dusty bodies far from the sun through mainly rocky bodies at Mars distances to the end of the sequence at Mercury, presumably because closer to the sun much of the dust and planetesimals have been vaporized and swept away, leaving only the most refractory elements to form the planet. The other aspect of Mercury is its magnetic field and associated magnetosphere. The origin of the field is mysterious, since it hardly seems probable that the core is still liquid, because such a small planet cools down rather fast. The magnetosphere should be strongly affected by the solar wind, which should be some ten times stronger than on the Earth. Moreover, the magnetospheric structure is different, because in contrast to the earth, Mercury is devoid of an ionosphere and an electrically conducting surface. The instruments for the Mercury mission have not yet been selected. Certainly there will be cameras to image the heavily cratered surface and determine its mineralogical composition, instruments to determine the elemental composition from fluorescent X-rays, magnetometers and analyzers of the plasma and of energetic particles in the magnetosphere. The detailed orbits of the two spacecraft should give information on the internal structure of the planet. Much interest was attached to the mission because 60% of the surface had never been observed and because of the mystery of the magnetic field. However, NASA has launched its “Messenger” mission in 2004 which should arrive at Mercury in 2009. Even though Messenger is perhaps a somewhat more modest spacecraft, the risk is that much of the cream will have been skimmed off by the time BepiColombo will be launched. It is not clear that this has led to a drastic review of ESA’s planning. In the meantime the mission has been placed on hold because of cost overruns. Surveying the overall program of planetary/cometary exploration, there is much that is very positive. The cometary studies are worthwhile scientifically, but the decade between launch and mission completion for Rosetta is very long for enthusiasm to be maintained. Mars Express and Huygens have been highly successful and Venus Express looks quite promising, but all risk to be one-shot-affairs without follow up and continuity. NASA with its much larger budget could afford a very varied program. One may wonder if ESA, with its more modest means, would have been better off by putting all its eggs in one basket in concentrating on one or two planets in a continuing program of studies that also could lead to a more active participation of a

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larger community of geologists, geophysicists, climatologists and even biologists. The total cost of the ESA planetary/cometary program 1990–2010 is of the order of 2300 M€ , including the cost of instruments funded by the member countries. This is equal to ten Mars-Express like missions. So one could have had a sustained autonomous European program of every two years a small mission to Mars or Venus or, more reasonably, every four to six years a larger one. European laboratories then could have used part of their national funding to participate in missions by others to comets and to other planets. The final science mix might not be so different, but Europe would have at least one planetary program, fully autonomous and with good continuity. In fact, Mars might have become for a significant part terra europea!

XIII. European Space Missions: The Sun and the Heliosphere; Ground based Solar Telescopes

Deus Sol Invictus

The heat generated by nuclear reactions in the solar interior is transported outwards by radiative leakage until in the outer layers convective motions are induced. The dynamo action resulting from convection combined with rotation generates magnetic fields. The interaction of the gas flows and the magnetic fields leads to much complexity. In some places the magnetic forces dominate, in others the flow drags the fields along. A variety of hydromagnetic waves are generated, while in places oppositely directed magnetic fields meet and annihilate each other. Such processes heat the gas and/or accelerate charged particles to high energies. The result is that the outer envelope of the Sun, the tenuous corona, is at a temperature of a million degrees, while the photosphere – the level where most of the light is emitted – is much cooler at 6000 K. The precise mechanism of the heating of the corona is still uncertain. It is one of the subjects of active solar research. At the high temperature of the corona the solar gravity is insufficient to contain the gas which begins to stream outwards: the “solar wind”. Thus, the solar system is pervaded by outward moving gas with velocities of hundreds of km/sec and in this stream magnetic fields and energetic particles are dragged along. When major energetic events like solar flares or Coronal Mass Ejections occur, the solar wind may be enhanced. Ultimately the wind will hit the earth’s magnetosphere, and especially during such events the earth’s magnetic field is perturbed allowing energetic particles to reach lower altitudes. At 100 km above the surface they may excite atoms and molecules in the atmosphere, giving rise to the aurorae – the northern (and southern) lights. Less artistically they may also affect telecommunications and electricity lines.

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Early space research was very much involved with the study of the earth’s magnetosphere and the local solar wind. Even with small satellites significant results could be obtained. Certainly ESA’s origins were in magnetospheric science. By 1980 some nine European satellites had been launched to study the magnetosphere and the solar wind near the earth (the US total was closer to 50). In addition, national European space agencies had launched several magnetospheric satellites or placed instruments on US satellites. Germany had gone far into the solar wind to 0.3 AU with the two Helios probes which measured temperatures and particle distributions until the beginning of 1980, while Swiss instruments on several Apollo flights had measured its composition. When the solar wind first interacts with the magnetosphere, a “bowshock” is formed, followed by the “magnetopause”, the boundary of the earth’s magnetic field (Figure XIII, 1). Here we shall only further consider the domain down to the magnetopause, leaving the rest of the magenetosphere

Figure XIII, 1. The geometry of the upper magnetosphere. The solar wind comes from the left and at the bowshock interacts with the magnetic fields in the wind that pile up against the magnetopause where the earth’s field begins. On the other side of the earth in the tail the situation is more complex because oppositely directed fields are separated by only a thin neutral sheet. Sometimes magnetic flux of the solar wind is transferred and reconnected to the field of the earth. Also in the solar wind itself there is a neutral layer separating field lines from the solar poles. The four Cluster spacecraft following the red orbit can study these regions, with additional data coming from the two Double Star satellites an ESA collaboration with China.

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to the geophysicists. It is, of course, true that these separations are not always very precise, with particles and waves traversing the boundaries. The ESA satellite ISEE-2 would continue well into the eighties (1978–1987). NASA launched ISEE-1 at the same time and later ISEE-3. The first two International Sun-Earth Explorers were placed close to each other to study the structures near the solar wind interface. Both the bowshock and the magnetopause were found to be unexpectedly thin and variable, moving and oscillating with speeds up to 100 km/sec. Thereafter followed AMPTE (1984–89), a mission with three independent satellites – a US magnetospheric one, and one each from Germany and the UK. The latter two penetrated into the solar wind. A few clouds of lithium and barium were released and their subsequent evolution followed. During the nineties, the German Equator-S functioned in the high magnetosphere, but only for a few months, while the US launched “WIND” on which also ESA and France had instruments. Its apogee was beyond the lunar orbit, and so it could effectively measure the undisturbed solar wind. If we add it all up, then the number of earth orbiting satellites that reached the magnetopause or beyond during the period 1961–1979 was 16 for the US, 4 for the USSR and 2 for ESA. During 1980–1999 there were only 2 for the US, 3 for the USSR/Russia and 2 D, 1 UK, 1 Japan and a Czech minisatellite, less than half that of the previous two decades. In addition, various deep space probes also obtained data on the solar wind. Much had been learned about particles, waves and magnetic field structures, and on how stormy conditions in the solar wind propagate downward with effects even at the earth’s surface. Two fundamental questions remained to be answered. The solar wind was observed near the earth in the plane of the ecliptic, which is also close to the equatorial plane of the Sun. But the corona looks rather different in the polar direction, and so the first question was how does the solar wind change with solar latitude? The second question related to measurements in the earth’s magnetosphere. Since everything there is variable in time and in space, how can we distinguish the spatial variations from the temporal ones? While with the two satellites ISEE-1, 2 some spatial information had been obtained, the rapidity of the variations with time made unambiguous results not easy to obtain. This was the origin of ESA’s Cluster project – four independent satellites for simultaneous observations of particles, electric and magnetic fields. Launched in 2000, the four Cluster II satellites (Figure XIII, 2) are flying in formation in the neighborhood of the interface of the magnetosphere and the solar wind with mutual distances varying from 200 to 18,000 km. Comparison of their measurements allows a very precise analysis of discontinuities in the magnetic fields, particle and wave distributions. Cluster I was on the maiden flight of Ariane-5 in 1996. While this gave a free launch, unfortunately the rocket exploded and destroyed the four spacecraft. Subsequently, ESA decided to redo the mission, making use in part of instrument spares which had been used for testing or kept as a reserve. Cluster II was launched

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Figure XIII, 2. The four Cluster spacecraft. The various booms (some 50 m in length) measure electric and magnetic fields.

in 2000 on two Soyuz rockets. A further expansion of the Cluster program results from “Double Star”, a collaboration with China. One satellite in an equatorial orbit has been launched with a Long March rocket in December 2003 and the next one in a polar orbit followed in 2004. Half of the instruments on board are European, derived from Cluster, and half are Chinese. Both have been very successful and so a further enhancement of the results from Cluster may be expected. For the moment no future magnetospheric missions are in the ESA program. Perhaps, after the results from Cluster and Double Star will have been obtained, the scientific priority of the field will be somewhat lower. In fact, after the Cluster I disaster, it was said by some that Cluster II should be done very quickly, because otherwise much of the magnetospheric community would have retired. This seems certainly a remarkable motivation for a scientific mission! However, it remains the case that the earth’s magnetosphere is an intermediary between the solar wind and the upper layers of the atmosphere. As such it would seem important to continue monitoring events in the region, which would not necessarily require very large investments. Since the US still deploys several magnetospheric satellites and since minisatellites for auroral and other studies in this area have been within the reach of Sweden and other countries, it is not obvious that there is a need for ESA to develop new activities in this domain.

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To answer the question about the latitude dependence of the solar wind, it was necessary to send a spacecraft to fly over the solar poles. It is not easy to do this by a direct launch from earth, but by sending the spacecraft “Ulysses” first towards Jupiter and then have Jupiter’s gravity change the orbit in a major way, taking it out of the ecliptic, success was achieved. In 1994 for a few months Ulysses flew over the solar south pole and a year later the north polar region was reached. At this time the Sun was in the quiet phase of the 11 year Sun spot cycle, but six years later Ulysses would again reach the polar regions, this time at high solar activity. Instruments on board measure magnetic fields, the speed and composition of the solar wind, particles and waves of various energies, solar X-rays and dust particles. Perhaps the most important discovery of Ulysses was that the solar wind is strongly latitude dependent. While near the equatorial plane speeds of 400 km/sec are typical, at high latitudes values twice as large are found. Also the composition of the gas is different in the two cases. The magnitude of the radial magnetic field in the solar wind was found to be independent of latitude – contrary to what could be expected from the dipole type field at the solar surface. As a result of these findings, much more sophisticated models of the heliosphere have been developed with implications also for cosmic-ray propagation and the Sun’s effect on the earth’s climate. Ulysses had originally been conceived as a two-satellite cooperative mission between ESA and NASA. Each would be responsible for one of the two and the orbits would be such that they would arrive simultaneously above opposite solar poles. A detailed agreement was concluded which unexpectedly and suddenly, without any consultation, was cancelled by NASA because of budgetary problems. So finally only the ESA satellite was launched, albeit by the NASA shuttle and with some US instruments on board. As described by Bonnet and Manno1), this episode had a very negative effect on ESA-NASA cooperation. Further studies of the solar wind are being made by SOHO, the SOlar and Heliospheric Observatory, which is a happier ESA-NASA collaborative venture. The main purpose of SOHO was the direct observation of the Sun in the visible, uv and extreme uv. Most of the instruments take spectra with good angular resolution or obtain images in broad or narrow spectral domains. Others measure the solar irradiance with high precision or study various types of solar oscillations, both in velocity and in irradiance. The solar irradiance, its spectral distribution and its relatively slow global variations are, of course, essential for the modelling of the earth’s climate. The rapid, but miniscule oscillations in irradiance and in velocity over the solar surface are evidence of sound waves in the solar interior. Since the velocity of sound depends on temperature and more weakly on other parameters, the observation of these oscillations gives very detailed information on the structure of the solar interior. The oscillations also give information about the internal rotation in the Sun. A very large number of oscillation modes are superimposed. These waves were first detected by ground based radial velocity observations. Long continuous data sets are needed to disentangle the

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different wave frequencies. Following some five days of continuous observations by the French in Antarctica, a number of consortia, BISON based in the UK, Iris in France and GONG in the US, were set up which placed measuring equipment at sites in countries at different longitudes so that the Sun could be observed 24 hours a day. However, clouds may intervene from time to time and atmospheric transmission variations limit the accuracy. One of the great advantages of SOHO is that it is located at the inner Langrangian point L1 from where it can observe the Sun with the same instrument without interruption 24 hours a day for a long time. L1 is a point some 1.5 million km sunwards from the earth, where spacecraft may be maintained in an orbit without much expenditure of fuel. A list of SOHO instruments is given in Table XIII, 1. In ESA SOHO began as DISCO which was proposed in 1980. It would have included instruments for studying solar oscillations, irradiance variations and the solar wind. It was not selected, but six years later it would be revived as SOHO in an ESA–NASA cooperation. Table XIII, 1. The SOHO instruments.

Twelve instruments constitute the SOHO payload as follows: SUMER (D) CDS (UK) EIT (F)

UVCS (US) LASCO (US) SWAN (F) GOLF (F) MDI (US) VIRGO (CH) CELIAS (CH) COSTEP (D) ERNE (SF)

Chromospheric and Coronal uv spectra 500–1600 Å, spectral resolution ~ 30,000, angular resolution ~ 1”3 Coronal spectra 150–800 Å, spectral resolution ~ 3000, angular resolution 3” Extreme uv Imaging Telescope full disk images in spectral lines originating at different levels in the chromosphere and corona, angular resolution 2”5 (Figure XIII, 3) Extreme uv coronographic spectra till 10 solar radii Coronographs and spectra till 30 solar radii Anisotropies and variability of the solar wind from Lyman-alpha measurements Large scale solar oscillation modes Small scale solar oscillation modes Irradiance oscillations and “solar constant” Charge, element and isotopic composition of particles up to 1 MeV/charge Energy distribution of ions (H, He) and electrons Energy distribution and isotopic composition of ions and electrons.

Only the country of the principal investigator is listed, but most ESA countries participated in one or more instruments.

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SOHO has produced a wealth of data. Analyses of the oscillations have shown that while the slower rotation of the photosphere surface at the higher solar latitudes persists through the convection zone, the interior rotates uniformly as a solid body. Flows from the equator to the pole extend down to at least 0.8 solar radii from the center at speeds of about a solar radius per year. Deeper down the flow must reverse sign if a pile up of matter at the pole is to be avoided. Such a flow pattern is important for understanding the dynamo which generates the solar magnetic field. “Blinkers”, half hour long flashes of extreme uv radiation in the quiet sun, discovered by SOHO, give evidence that magnetic reconnection and dissipation take place continuously in the quiet Sun. Small bipolar magnetic structures have been observed by SOHO to emerge randomly in the photosphere and then to be moving to the boundaries of the large scale supergranules. There field lines of one polarity cancel the existing ones, which are replaced by the field lines of the other polarity. In the process the connections between field lines change. In less than two days the whole field at the boundaries is replaced. The origin of these small bipolar areas is mysterious, but their dissipation is undoubtedly important for the processes which heat the corona. From the spatially resolved spectra of the Sun detailed information on density, temperature, composition and velocity of individual parcels of gas may be obtained. The electron temperature in coronal holes is too low for effective acceleration of the solar wind, which suggests that it is due in part to the direct momentum transfer from magnetohydrodynamic waves. The outflow of different ions has different velocities and is variable, and as a consequence also the composition varies in space and time. So it is no surprise that the composition of cosmic rays accelerated in flares may be very different from the overall composition of the Sun. Of much interest are the coronal mass ejections – huge eruptions in the corona caused by a magnetic instability – which later may cause magnetic storms on earth. As a result of SOHO, the prediction of “space weather” may become more accurate. H. Kreuz long ago identified a small group of Sun grazing comets which passed at only a million km from the Sun, well inside the corona. Among these the comet of 1882 was particularly brilliant and after perihelion had broken up in four parts, undoubtedly with many smaller fragments. SOHO has discovered a thousand comets of the Kreuz class which would seem to represent the fragments of this or a similar comet. Most of these do not survive their perihelion passage. One future solar mission is foreseen in the long term ESA program. Somewhere in the 2010–2015 time frame “Solar Orbiter” should be launched by ESA or possibly be undertaken as a joint project with another agency. The spacecraft would be placed into an elliptical orbit with perihelion (closest approach to the Sun) at some 0.21 AU or 45 solar radii. At that distance the solar surface may be studied with unprecedented resolution (35 km pixels, corresponding to 0.05 arcsec as seen from the earth). In addition near

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Figure XIII, 3. The Sun observed with EIT on SOHO. The four images have been taken in narrow spectral bands around spectral lines emitted by gas at different temperatures by the Extreme-ultraviolet Imaging Telescope on the ESA-NASA SOlar and Heliospheric Observatory. Clockwise from the upper left are lines from: 14 times ionized iron Fe XV (28.4 nm), Fe XII (19.5 nm), Fe IX + Fe X (17.1 nm) and singly ionized helium He II (30.4 nm) corresponding to temperatures of respectively 2, 1.5, 1.0 and 0.05 million K. The first three are typical coronal lines, while He II originates in the complex transition region between the hot corona and the relatively cool chromosphere. At the He II level the chromospheric network is visible which results from convective motions below the solar photosphere interacting with magnetic fields. Also some prominences are seen which represent cool magnetically supported gas in the corona. At the higher temperatures typical coronal structures with magnetic loops dominate the picture, as well as activity related to the dissipation of magnetic energy. The connection to two sunspot groups at photospheric level is clear in all four images.

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perihelion the angular orbital speed of the satellite and that of the solar rotation match, so that the satellite hovers for some time over a fixed area on the solar surface and can study its evolution in exquisite detail. Moreover, the orbit would be tilted so that higher latitude areas may also be observed. Solar Orbiter would be equipped with high resolution imagers in visible and far uv light, spectrometers, and a magnetograph to measure magnetic fields. In addition, the solar wind would be studied in situ closer to the Sun than ever before. Solar maximum is predicted to occur around 2011–2012 and could be optimally observed if a launch early in 2009 were possible, which may be difficult financially. If not, the mission would observe the declining phase of solar activity unless one would wish to wait till the next solar maximum eleven years later. Technologically the mission is challenging since at 0.21 AU the solar radiation is some 23 times more intense than near the earth. So preventing excessive heating of the spacecraft and instruments is a major problem. An even more ambitious mission would be “Solar Probe” which was already proposed in Horizon 2000 as a “green dream” for an indefinite future. It would approach the Sun to within a few solar radii (0.03 AU) and make in situ observations of the corona in the region where the solar wind originates. While Solar Probe has frequently been discussed in various contexts, the technical and financial aspects are so forbidding that no specific plans have yet been made. Both the US and Japan have launched their own solar missions in the post 1980 period. The Hinotori satellite from 1981–1991 and especially Yohkoh from 1991–2001 made major contributions. The X-ray images obtained by the latter were spectacular and informative on flare phenomena. The UK made a major contribution to the Yohkoh instrumentation. A new Japanese mission Solar B (with US, UK) is planned for 2005. Its optical telescope should have a resolution of 0.2 arcsec, corresponding to 150 km on the Sun. Also uv and X-ray instruments are included. Following the Solar Maximum Mission (1980–1989) with contributions from UK, NL, and D, and several spacelab based short missions, NASA launched in 1997 the Advanced Composition Explorer which measures elemental and isotopic abundances from H to Ni in the solar wind and in low energy galactic cosmic rays. It has been placed at L1. It was followed in 1998 by the Transition Region And Coronal Explorer which has taken images of the Sun in the light of spectral lines corresponding to different temperatures. It has a higher angular resolution than the EIT instrument on SOHO, but can image only a small part of the solar disk. In 2001 came Genesis, a spacecraft which collected solar wind material at L1 and returned it to earth for analysis in 2004. A soft X-ray imager on the meteo satellite GOES-12 now takes a whole disk image every minute. The Ramaty High Energy Solar Spectroscopic Imager launched in 2002 is obtaining γ-ray images of the Sun with unprecedented angular resolution to study flare phenomena at the highest energies. A contribution to this mission was made by the Paul Scherrer Institute near Zurich. In late 2005 NASA intends to launch STEREO, a set of two spacecraft one

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ahead of the earth in its orbit and one behind. Contributions to the instrumentation have been made by F, D and the UK. It should obtain stereoscopic images of the Sun as well as threedimensional information on Coronal Mass Ejections. In 2007 it would be followed by the Solar Dynamics Observatory. The US has also launched military satellites for solar observations. Russia returned to the solar scene with KORONAS-I (1994–1995) and KORONAS-II launched in 2001. The latter, with contributions from Georgia, PL, D, F, UK and US, has several X-ray and uv imagers and spectrometers, a coronograph and photometers. For the future, Koronas-Photon is planned to observe γ-rays and neutrons. Also China is considering a solar satellite with a 1-m optical telescope and other uv and X-ray instruments. If we survey these programs (Table XIII, 2) it is clear that, though Europe has made a more than respectable showing with Ulysses and SOHO, it is far from being the leader in the field. With Solar Orbiter long into the future, this is unlikely to change. Table XIII, 2. The solar missions of ESA, Japan, NASA and Russia.

EU

Japan

NASA

Russia

1980–89 1/2 Ulysses; Hinotori; X solar wind

Solar Max; v, uv, X, γ 1/2 Ulysses; solar wind

1990–99 1/2 SOHO; v, uv

Yohkoh; X

1/2 SOHO; v, uv ACE; solar wind, CR Koronas-I; radio-γ TRACE; v, uv

2000–09

Solar B; v, uv, X

Genesis; solar wind RHESSI; γ 2 STEREO; v, uv

Koronas-II; radio-γ Koronas-Photon; γ, neutron

SDO; v, uv

Ground based solar telescopes Ever since Galileo and his contemporaries watched the dark Sun spots on the solar disk, observations of the Sun with relatively small telescopes have continued. Because of the importance of events on the Sun to conditions in the ionosphere, the auroral belt and even lower down, institutes in many

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countries monitor the Sun on a daily basis. While this activity has been useful, progress in solar physics now demands more optimized facilities. Space facilities have many advantages in giving access to the wavelengths that are inaccessible from the ground, as well as in the study of the corona. However, for investigations of the photosphere and its magnetic fields and for studies of the elemental composition of the Sun, the larger ground based telescopes remain essential, especially when provided with adaptive optics (AO). Since the photospheric magnetic fields determine much of the structure of the fields in the corona which are difficult to observe directly, coordinated programs of space and ground based solar observations have been particularly useful. In fact, one third of the SOHO observations were coordinated with observations from the ground. Here we shall only mention the most important of the ground based European facilities. THEMIS started out as a French project in which Italy now participates at the 15% level. Inaugurated in 1996, various problems, partly financial, have slowed down the progress of the 90 cm telescope placed at the Observatorio del Teíde on Tenerife (Figure VI, 1). It has been constructed to be free of instrumental polarization so that solar magnetic fields can be measured with maximum sensitivity. Two German telescopes, also at Teíde, with apertures of 70 cm and 45 cm, have been operating for almost 20 years, obtaining mainly high spectral resolution data. The 70-cm is being equipped with AO, while the 45-cm will be replaced in 2005 by a 150 cm AO telescope “GREGOR”, which will be one of the two largest solar telescopes worldwide, the other being at Kitt Peak in Arizona. Two other solar telescopes have been placed at La Palma. The new Swedish instrument, with a 97 cm fused silica lens and an adaptive optics system, aims for the highest possible angular resolution of about 0.1–0.2 arsec. The Dutch Open Telescope (45 cm) is testing a novel technology in which the wind prevents overheating. Countless other solar telescopes operate in Europe and in the rest of the world, with variable impact on the research field. While long term continuity of solar observations with the same instrument has a great value in providing uniform data sets over long periods, an overdue consolidation appears to have begun. For a number of years JOSO, the Joint Observatory for Solar Observations, conducted site selection campaigns, among others in the Canary Islands. A more formal organization, the LEST Foundation (Large European Solar Telescope), was founded in 1983 at the Royal Swedish Academy of Sciences. When there seemed to be a prospect of non-European participation, the meaning of the “E” was changed to “Earth-based”. A design study of a 2.4-m telescope was made. However, real funding proved elusive. The French were fully engaged with the underfunded THEMIS, while the US was starting to plan its own telescope. So the LEST program has been terminated, while the US now is looking for international partners for its 4-m project! Observations of the radio emission from the sun provide much additional information. At long wavelengths (~ 1 m) the radiation comes from the

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corona, while at a few cm the cooler photosphere is also observed. The Nancay (F) radioheliograph was developed in 1967 and renovated in 1996. It regularly observes the corona at 10 wavelengths between 70 and 180 cm and is particularly suited for the detection of coronal mass ejections which later may perturb the solar wind and the earth’s magnetosphere. At Zurich observations are made in the 7-30 cm range. In the US a powerful facility is being planned, the Frequency Agile Solar Radio Telescope. It would operate over the 1.2-600 cm wavelength range with angular resolutions down to 0.8 arcsecond at 1.2 cm and a field of view of 70° at 600 cm.

XIV. Astroparticles and Gravitational Waves

Die experimentelle Begründung der Einsteinschen Gravitationstheorie ist also noch nicht weit gediehen. Wenn die Theorie aber trotzdem schon heute den Anspruch auf allgemeine Beachtung erheben kann, so hat das in der ungewöhnlichen Einheit und Folgerichtigkeit ihrer Grundlagen seinen berechtigten Grund. Erwin Freundlich1)

While most astronomical information comes to us through visible light and other electromagnetic radiation, there are additional channels through which information about cosmic events may reach us: energetic particles, neutrinos and gravitational waves2). The particles, the cosmic-rays (CR) were discovered by Victor Hess in 1912. During balloon flights he showed that a mysterious source of ionization increased with height in the atmosphere, indicating that its cause was outside. Clarity about the nature of CR was only obtained during the thirties when it was concluded that they are composed primarily of energetic protons. At first they were utilized mainly as a convenient source of energetic particles for particle physicists during the pre-accelerator days. Only in the early fifties was their astrophysical significance fully realized, in particular due to the work of Vitali Ginzburg and his associates in Moscow. Neutrinos were hypothesized by Wolfgang Pauli in the thirties to explain certain aspects of radioactive decays. Experimental confirmation came in laboratory experiments in 1955. Neutrinos have little interaction with matter, which makes their detection very difficult. Gravitational waves were predicted by Einstein on the basis of his 1916 General Relativity Theory. They represent waves in the fabric of space-time. The validity of the theoretical prediction remained somewhat uncertain until the middle of the century. Indirect evidence for their existence has been obtained, but direct observation still has eluded us.

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Cosmic-rays The energies of cosmic-ray particles cover an enormous range from some MeV to values at or above 1020 eV (~ 10 joule = 10 wattseconds). Few particles of the highest energies arrive on earth, perhaps one above 1020 eV per km2 per century! But they are of much interest because nobody has an idea what they are or where they come from. Speculation abounds that they may represent some new type of particle, but this need not be the case. If these particles of the highest energies are protons, they cannot come from more than a few hundred million light years away, since collision with photons of the Cosmic Microwave Background would have destroyed them. At these energies plausible (inter)galactic magnetic fields would not deflect them very much, and so we might be able to trace them back to their places of origin. The rarity of the highest energy particles implies that no direct observation is possible. However, when such a particle strikes the atmosphere it collides with oxygen or nitrogen nuclei. The result is an Extensive Air Shower (EAS) of secondary particles, principally electrons (and positrons), but also muons and some hadrons. The shower extends over an area of some 10 km2 with on average 1000 electrons per m2. To characterize the shower it is sufficient to sample it with detectors distributed here and there over a large area. The most important early arrays included Haverah Park in the UK and Volcano Ranch in the US. They have been superseded by EAS arrays at Yakutsk in Siberia and the very large Japanese AGASA array at Akeno which covers 100 km2. The most interesting result from AGASA are four pairs and two triplets of events above 4 × 1019 eV coming (within the angular resolution) from the same directions. If confirmed, this would suggest that discrete sources are seen. However, the world total of claimed > 1020 eV events still is less than two dozen. The small number of detected events makes everything still quite uncertain, and bigger arrays are needed. A large 13 country collaboration, including several European countries, is constructing the Pierre Auger Observatory (PAO), which will consist of two large arrays, one for each hemisphere. The southern component in Argentina consists of an array of 1600 detectors distributed over a 3000 km2 plateau. It should be fully operational in 2006. It is planned to build thereafter a northern array in Arizona or Utah. With these arrays the number of high energy events detected should increase by an order of magnitude or more. After a few years of operation the PAO may detect a hundred events with energies above 1020 eV, if they really exist. In any case, some several thousand events in the 1019–1020 eV should be observed (Figure XIV, 1) and the directions from where they come measured. The size of the PAO has been set such as to keep the cost below 100 M€. Another way to detect the air showers is to optically observe their tracks through the atmosphere. The energetic electrons and positrons will excite the

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+5 20 Log F (>E)

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Figure XIV, 1. The flux of cosmic-rays. The curve gives the integral, omnidirectional flux (particles per m 2 and sec, vertical scale) of particles with energy larger than E(eV) (horizontal scale). In the insert the steep slope has been eliminated by multiplying the flux with E 1.7 , which makes it easier to see the “knee” around 10 15 eV and the flattening around 1019 eV. Note that the scale for E1.7 F(> E) indicated on the right hand side is different.

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nitrogen molecules in the air. This results in nanosecond (10-9 s) fluorescent light flashes which may be observed by large telescopes, which are relatively cheap because optical quality need not be very high. At the focus a multiple set of fast photomultipliers (fly’s eye) is placed to detect the flashes. With this method one may survey a larger area for showers than with the existing EAS arrays, but, of course, only during clear moonless nights. Fly’s Eye in Utah operates on this basis. The precise intercalibration of the two methods is far from trivial and the results from Fly’s Eye and AGASA are partly contradictory. To resolve these problems the PAO will be a hybrid array with four telescopes to also obtain stereoscopic images of the fluorescent tracks. A smaller 900 km2 hybrid array is being built in

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Utah by a Japan-US cooperation, in order to get an improved capability in the northern hemisphere more quickly. Even larger areas may be surveyed from space by a wide angle camera that looks down imaging a large stretch of the earth’s atmosphere. The Extreme Universe Space Observatory, EUSO, is a project under evaluation at ESA. It could be attached to the European Columbus module on the International Space Station at 400 km altitude. EUSO (Figure XIV, 2) would survey some 170 000 km2 of the atmosphere, 60 times the effective area of the first half of the PAO. However, the gain would be less because of clouds and the need for night time observations. NASA is considering a similar project which would consist of two satellites at 1000 km altitude surveying an area still three times larger than EUSO. Both projects should detect events above several times 1019 eV. The more numerous cosmic-rays at lower energies have been studied with a variety of the standard detectors of nuclear physics carried first by high altitude balloons and later by spacecraft. The UK satellite Ariel 6 (1979–82) determined abundances of heavy elements. Subsequently, NASA’s Long Duration Exposure Facility remained in orbit for 69 months before being recovered. It included solid-state nuclear track detectors, provided by Ei, F and UK, which reliably determined the abundances of elements around uranium. The bulk of the CR are almost certainly accelerated in or around supernova remnants, and it had been thought that such elements might be overabundant, being produced in the supernova process. However, the result of all of this work is that the abundances of most elements in the source regions of the CR are disconcertingly normal. Apparently, the CR are accelerated mainly in

Figure XIV, 2. The proposed EUSO instrument. Attached to the ESA Columbus External Payload Facility at the International Space Station, it would observe the nitrogen fluorescence and the reflected Cerenkov radiation generated by very high energy cosmic-rays passing through the earth’s atmosphere.

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interstellar space by the shock waves generated by the supernovae rather than in the material of the supernova itself. Isotope abundances have also been determined by Ulysses and in particular by NASA’s Advanced Composition Explorer, which was launched in 1997 and placed at the inner Lagrangian point L1. It measures the composition of the solar wind and of relatively low energy CR. The energy distribution of the cosmic-rays is quite steep (Figure XIV, 1). For every decade increase in energy there are globally 50 times fewer cosmicrays above that energy. Around 1015 eV this increases to about 100, creating a “knee” in the steepening distribution. It is believed that at that energy the particles begin to leak out of the Galaxy or that the supernova shocks are becoming less effective accelerators. In either case it could be expected that the composition would begin to shift to heavier nuclei with a larger nuclear charge, since these are more tightly coupled to the magnetic fields. To determine the composition at that energy a precise analysis of all the components of the resulting air showers is needed, but analysis of data from arrays of a few hundred meters diameter suffice. The most convincing results have been obtained by KASCADE (D with PL, Armenia, Romania), which was constructed to study particles around the “knee” and consists of several hundred m2 of detectors spread out over a 200 × 200 m2 area in 252 detector stations. Since all three of electrons, muons and hadrons are detected, relatively reliable inferences on the global composition of the incoming particles can be made. These show that, in fact, the heavier particles with larger charge become more abundant after the “knee”. A similar result was obtained by the EAS-TOP and the MACRO cooperation. The MACRO detector was built under the Gran Sasso mountain in halls that were excavated for the building of the Rome to L’Aquila highway tunnel. A number of other physics and astrophysics experiments are also conducted there, since the km thick layer of rocks overhead shields the detectors against unwanted particles. The MACRO detector was operated from 1989–2000 to look for exotic particles (monopoles, etc.), neutrinos and muons. When a high energy cosmic ray particle strikes the atmosphere, the resulting Extensive Air Shower of electrons and positrons is detected on the ground near the top of the mountain, while the muons may make it to the MACRO detector. Again, comparison of the two components gives some information on the overall composition of the cosmicrays near the “knee”. There is one other area where it is remotely possible that cosmic-rays could make a significant contribution, this is the search for antimatter. In our neighborhood in the Universe there is matter, but no antimatter. If there were antimatter in our Galaxy, it would be rapidly annihilated with copious production of γ-rays. In the cosmic-rays there are some antiprotons which result from collisions between energetic CR and the interstellar gas. Such collisions can make antiprotons, but are too destructive to synthesize complex antinuclei. If there were regions of antimatter in the Universe, they could be

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sources of antimatter CR. This has led to the AMS (Alpha Magnetic Spectrometer) experiment in which antihelium nuclei are looked for. A first shuttle based attempt did not yield evidence for such nuclei, and a second attempt should be made with a massive detector placed on the Space Station. Several European countries participate in this US led project. In conclusion, we have learned much about cosmic-rays during recent decades, though the precise mechanisms and places of acceleration have not yet been fully established. However, above 1016 eV our ignorance is almost total. From this brief survey it is clear that Europe has made an entirely respectable contribution to the field, though it is not quite the world leader.

Neutrinos While the charged cosmic-ray particles are affected by magnetic fields, photons and matter along their path, neutrinos can move along straight lines almost totally unhindered by matter or magnetic fields. As a consequence, the direction from where they come points directly to their place of origin. However, the fact that they interact so little with matter makes their detection very difficult. In the sources of high energy cosmic-rays, collisions with matter may produce energetic neutrinos which could be detected on earth. Enormous detectors are needed to obtain a signal. Neutrinos which pass through the earth interact with the rocks and produce upward moving muons which may be detected from light flashes they produce in transparent media, like water or ice. The detectors need to be placed at a large depth to reduce the flux of particles coming from above. Two European detectors are being prepared: NESTOR (GR with I, F, Rus) at a depth of some 3 km, and ANTARES (F, other EU) at 2 km, both in the Mediterranean near the Greek and French coasts respectively. In these detectors photomultipliers to detect the light flashes hang down from the surface of the sea on strings. Obviously, areas of very calm, transparent water are needed where the light may be seen from distances of several tens of meters. Earlier experiments were done in Lake Baikal, known for its pure waters. The US, with German participation, has built an ice based detector, AMANDA, at the South Pole. Strings of photomultipliers are hung in holes drilled into the ice. Between now and 2010, AMANDA is expected to be gradually upgraded to ICECUBE by a large international cooperation involving D (15%), S, B, NL, J and Venezuela. Upon completion a total of 4800 fast photomultipliers on 80 strings will be mounted deep under the ice surveying events in a km3 of ice. The detector will come on line gradually with every new string added beginning to take data almost immediately. So far no high energy neutrino from beyond the earth has been detected, but interesting data about luminescent organisms in the depths of the sea are being obtained!

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Low energy neutrinos are produced in the nuclear reactions which power the sun, and they can easily escape from the solar interior. Two seminal ideas in the field are due to Bruno Pontecorvo, the Italian physicist, who fled to Moscow in 1950. He proposed in 1946 to detect neutrinos through the reaction neutrino + 37chlorine → 37argon + e–, and about a decade later he suggested that neutrinos could oscillate between various states. Somehow the second idea which resolved the “solar neutrino puzzle” was insufficiently appreciated at the time. The resulting goose chase has led to an avalanche of papers concerning the solar interior, even though the solution was so simple. The chlorine reaction was exploited in a deep gold mine in North Dakota. A huge tank of C Cl4, a very cheap liquid was from time to time searched for the radioactive argon produced by the solar neutrinos. Some was found, but only about a third of the predicted amount. Since the neutrinos in question come from a reaction which is rather sensitive to the temperature distribution in the solar interior, the first thought was that something was wrong with the solar models. Confirmation of the observations by a different technique came from (Super)Kamiokande in Japan. Subsequent experiments involved the low energy neutrinos emitted during the basic energy generating reaction in the Sun. Even without a model one could predict that neutrino flux from the total energy radiated by the Sun. GALLEX, the GALLium EXperiment (I, F), installed in the Gran Sasso laboratories in Italy, involves 30 tons of Gallium to measure the reaction 71Gallium + neutrino → 71Germanium + e–. SAGE, a Russian-US experiment, using 55 tons of Gallium, in the underground laboratory at Baksan in the Caucasus has, after initial disagreement, confirmed the GALLEX result. Again it is found that the observed rate is lower than predicted. Subsequently, KamLAND, the successor to Kamiokande, demonstrated the existence of neutrino oscillations, by observing neutrinos from surrounding nuclear reactors. There are three flavors of neutrinos: νe, νμ and ντ. Apparently the neutrinos can oscillate between the three flavors. So an experiment capable of detecting only one of them is likely to observe fewer than expected. The Sun emits only electron neutrinos. On the way to Earth they transform in part into νμ and ντ. The definitive proof has come from the Sudbury Neutrino Observatory in Canada (Can, US, UK). It involves 1000 tons of heavy water (D2O) which allows all three flavors to be detected. In fact, the total flux of all three is about equal to the flux of νe expected from the solar models. Incidentally these results also imply that neutrinos have mass, although the mass is very small, too small to be of interest as a dark matter candidate. In addition to those from the sun, two dozen neutrinos have been detected by detectors in the US and in Japan from the 1987 supernova explosion in the Large Magellanic Cloud. Thus, so far neutrinos have been detected only from two cosmic sources.

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Dark matter The matter we see in the form of stars and gas is only a small part (~ 10%) of all matter in the Universe. The rest is “dark matter”. In our own Galaxy there is evidence for its existence because the gravity inferred from stellar motions is stronger than what could be expected from the visible matter alone. The nature of the dark matter is still entirely unknown. Among the possibilities are particles beyond the current “standard model” of the particle physicists. A variety of proposals have been made for their direct detection. Some of these have been investigated experimentally in Europe, among others in the underground laboratories under the Gran Sasso. It would take us too far into the domain of particle physics to discuss these here. Alternatively, indirect evidence might be obtained if such particles and their antiparticles annihilate with the emission of neutrinos or γ-rays. For example, WIMPs, Weakly Interacting Massive Particles, could be captured by the sun and there produce high energy neutrinos observable with the detectors already discussed. Since the thermonuclear reactions in the Sun produce only low energy neutrinos, a clear result could be obtained. It has also been suggested that the annihilation of such particles at the galactic center could generate a flux of energetic γ-rays measurable with instruments like HESS. In fact, HESS (chapter XI) has found a source there, but its spectral characteristics did not fit with the expectation for WIMP annihilation.

Gravitational waves According to Einstein’s theory of gravity (the “General Theory of Relativity”) any non axisymmetric motion of matter generates “gravitational waves”, waves in the fabric of space–time. In fact, the existence of such waves has been indirectly confirmed by the orbit of the “binary pulsar”, a close binary of two neutron stars. The orbital energy is gradually lost owing to the emission of gravitational waves in quantitative agreement with theoretical expectations. Gravitational waves may be emitted in various processes. Before a supernova explodes, part of the star implodes. When this process is spherically symmetric no gravitational waves are emitted. But when the star rotates fast enough, the resulting asymmetries lead to gravitational waves, though quantitative predictions depending on the degree of asymmetry are difficult to make with confidence. The collapse process towards a neutron star or black hole is very rapid and the wave frequencies involved should be of the order of 1000 Hz. It should not be too complicated to detect the gravitational waves from a supernova in our Galaxy, but such events occur only about twice a century. So we may have to wait a long time! Under favorable conditions some supernovae might be observable out to the distance of the Virgo cluster

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(~ 50 million light years) and so a higher frequency of events would perhaps be possible. Very compact stellar mass binaries typically may have periods of a few thousand seconds, corresponding to wave frequencies in the 0.001 Hz range. When such binaries are sufficiently close to the Sun these waves might be detectable. The energy loss in the form of gravitational waves will cause the two stars to spiral inwards and ultimately to merge. For solar mass stars with separations like that of the Sun and the earth (1 AU), this process would take much longer than the age of the Universe. However, some binaries are known which are much closer. For the “binary pulsar” composed of two neutron stars with a separation of 0.006 AU, this would take only some 400 Myr. So there should be many such systems in the Universe which achieve coalescence. An even stronger signal would result when two black holes merge. Neutron stars or black holes of stellar mass falling into supermassive black holes at the centers of galaxies also would give strong signals. The waves with frequencies of the order of 1000 Hz have wavelengths of a few hundred km. They may be detected by measuring with high precision the changes in the distance between two test masses as the waves pass by. Extreme precautions have to be taken to ensure that natural seismic or man-made noise does not perturb these test masses. Laser based interferometers measure the infinitesimal displacements of these masses as the waves pass by. Since the relative displacements are proportional to the length of the instruments, typical setups have dimensions of the order of one or more km. However, other factors also play a role in the final sensitivity, in particular the suppression of seismic noise. Construction has just been completed near Pisa of “VIRGO”, a French-Italian detector with arms of about 3 km at a cost of some 70 M€ (Figure XIV, 3). Seismic “super attenuators” ensure extreme protection against noise sources. A smaller German-UK project “GEO 600” has been constructed in Germany. In the US two 4 km long facilities (LIGO) have been completed, and in Japan a smaller experimental facility of 300 m, TAMA, is operational. It seems very uncertain that these detectors have the sensitivity required to see more than a few events per year. So plans for VIRGO II or LIGO II are already being made, with in Germany a tendency to participate in the US project. The LIGO upgrade alone is budgeted at 185 M$. Since false events may easily occur in a single detector, it is important to have a means to confirm the reality of what is observed. To achieve this, VIRGO and the two LIGO detectors exchange data in real time. If all three see the same event, it should be real. There are, however, severe limits to what may be achieved on the ground at lower frequencies. Small movements of the soil or even changes in the density of the air which are dragged along by the wind already limit the accuracy at frequencies around 1 Hz. The only solution for observations at frequencies in the mHz range is to place the equipment in space.

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Figure XIV, 3. VIRGO. The French-Italian gravitational wave detector is located near Pisa. A laser beam is split in two and travels down the two 3 km long arms, to be reflected by mirrors at the ends. The beams are reflected back and forth numerous times before being recombined at the central station. The resulting interference pattern would be modified if gravitational waves pass by the facility.

LISA, the Large Interferometer Space Antenna, was proposed as a cornerstone in the Horizons 2000 program of ESA. It also appears in NASA’s long term planning. LISA (Figure XIV, 4) would be composed of three spacecraft separated by about 5,000,000 km. Again the separations would change when gravitational waves pass by. Though the changes are minuscule, they could be measured with the required precision by exchanging laser beams between the satellites. LISA may be realized a decade from now, perhaps as an ESA–NASA collaboration at a total cost (optimistically?) estimated at perhaps 400 M€. An earlier technology mission “LISA pathfinder” is also planned. Since many sources will affect the orbits of the LISA spacecraft simultaneously, problems of source confusion may be important. In any case, the data analysis problem appears rather formidable. The gravitational wave detectors represent experiments at the limit between physics and astrophysics. Not only will they directly demonstrate the existence of gravitational waves, the studies of black hole mergers will also explore the nature of space-time under conditions of extreme gravity, where Einstein’s theory could never be verified and where fundamental questions of physics remain open. It is also possible that in the future

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Figure XIV, 4. LISA. The three spacecraft of this ESA–NASA project detect low frequency gravitational waves by measuring their relative distances by laser interferometry. Separated by 5 million km, they trail the earth in its orbit by 20°. The plane defined by the three has an inclination of 60° with respect to the ecliptic, so that the triangular formation is preserved by the three orbits.

gravitational waves from the earliest phases of the Big Bang at the origin of the Universe will be observed. If so, they would give evidence about conditions closer to that singular event than any other observations. However, they may also create a background that makes the detection of other sources with LISA more difficult. The present prospects of VIRGO and LIGO are still limited. Perhaps some supernova related events will be seen. Alternatively, some black hole or neutron star coalescences will be observed. Our inability to predict the annual number of such events leaves a large range of possibilities. Current estimates suggest that LISA should be able to detect several close binaries whose properties are known from optical studies. However, their interest in testing General Relativity is limited since the gravitational fields involved are rather weak. They might be particularly useful in the experimental evaluation of the performance of LISA. Mergers of black holes would be more interesting. It has been frequently noted that if a binary of two million solar mass BH coalesces, LISA should detect the event anywhere in the Universe with a very high signal-to-noise ratio. Unfortunately, we do not know how frequent such events are; they may well occur much less than once a year. A more plausible source of gravitational waves might be the infall of BH with masses of some 10 solar masses into the massive BH at the centers of galaxies. Here the stellar density is high. So the frequency could be much higher, while such events could still be detected out to a redshift z = 1. Also infalling neutron stars or even white dwarfs might be detectable. Thus, there are many possibilities, though here also we are incapable to reliably predict to the frequency of occurrence. As a result, we also do not know what

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problems may result from source confusion. For example, if close white dwarf binaries are as common as some people think, a rather strong background of gravitational waves could result, which might make individual source detections more difficult. In any case, with so much uncertainty, all that can be done is to launch LISA and to see what there is to be discovered. Other more pure physics experiments also benefit from the weightlessness in space and from the absence of disturbances. At the heart of the General Theory of Relativity is the “principle of equivalence” which asserts that mass determined from gravity is the same as mass determined from inertia, independent of the nature of the matter. This has been verified on the ground to one part in 1012. The French “MICROSCOPE” mission, with ESA participation, to be launched in 2007 should improve this to one part in 1015, a factor of 1000 improvement. A large NASA mission “Gravity Probe B” launched in 2004 will check on specific predictions of Einsteinian theory around the rotating earth. One may wonder if it is justified to invest so much effort and money in fields like gravitational waves and physics experiments which have rather uncertain returns. However, the potential rewards are very large. The nature of gravity is fundamental to an understanding of physics and the Universe. Gravitational waves provide the only way to experimentally study strong gravitational fields. In combination with the subtle physics experiments they provide the only means to ascertain the adequacy of Einsteinian theory.

XV. Looking for Planets and Life in the Universe

It is in the highest degree unlikely that this earth and sky is the only one to have been created … You are bound therefore to acknowledge that in other regions there are other earths and various tribes of men and breeds of beasts. Lucretius1)

One of the great questions about the Universe – and not only for scientists – is whether earth-like planets orbit other stars and, if so, whether there is life on such planets. In antiquity Lucretius and at the dawn of the present era Giordano Bruno answered the question positively on the basis of general plausibility. Now, however, the issue is moving from the realm of speculation into the domain of scientific investigation and observation. Three methods for detecting exoplanets are available: measuring the reflex motion of the star around which the planet orbits, measuring the loss of light when the planet transits in front of the star, and direct imaging of the planet. The first two methods have produced results, though no earthlike planets have yet been detected. Direct imaging is, of course, the ultimate goal, but it is also the most difficult.

Stellar Reflex Motion When we say that a planet orbits the sun or a star, the statement is not entirely correct. Actually both orbit the common center of gravity. In the case of Jupiter and the sun the ratio of the masses is 1:1047 and so the sun is 1047 times closer to the center of gravity, and therefore its orbital speed is also 1047 times smaller. Jupiter’s average speed is 13 km/sec and so that of the Sun in its orbit is 12.5 m/sec or 45 km/hour. Of course in our solar system there are other planets which also contribute to the reflex motion of

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the Sun, but since the mass of Jupiter dominates over that of the others the result is not changed very much. The orbital motion of a star (Figure XV, 1) due to an exo-Jupiter would be detectable by the Doppler effect – the shift in wavelength of spectral lines when a star has a velocity component in the radial direction – along the line of sight. Most searches for planets were made initially on the assumption that other planetary systems would be like our own. Since Jupiter has an orbital period of around twelve years, no very frequent observations would be needed. Fortunately, Michel Mayor and Didier Queloz looked more frequently with their spectrographic device that allowed a precision of some 10 m/sec to be attained. In 1995 they detected2) the first exoplanet around the star 51 Pegasi, with a period of only four days. According to Kepler’s third law the planet, with a mass of the same order as that of Jupiter, is only some 0.05 Sun-Earth distances (Astronomical Units or AU) away from the star. Since the search for planets does not require observations of faint stars, the 1.9-m telescope at the Observatoire de Haute Provence was sufficient for the purpose. In the meantime, more than a hundred such Jupiters have been discovered, some with even 2-3 times shorter periods. Such planets would be even closer to the star and therefore very hot, more than 1000 °C. At such high temperatures a planet like Jupiter would begin to shed gas from its atmosphere. In fact, in one such system absorption by the escaping gas in front of the star has been detected3). It is now generally assumed that the Jupiter like planets have formed further out. They then would have spiralled inwards owing to the drag of material that was left around the newly formed star after the main period of planet formation had ended. What caused the planets to come so close to the star without falling into it, is still not very clear. In any case, these discoveries indicate that planets around other stars are not at all rare, but that our solar system with the major planets far out is far from typical. Figure XV, 1. A star and a planet revolving around the common center of gravity. In the drawing the relative radius of the planetary orbit is much smaller than in reality. When the star and the planet are as indicated by filled circles and >O when the observer O is more or less in the orbital plane, the planet shadows part of the star and its brightness is diminished. When the star and planet are in the position of the open circles a quarter period later, the approach velocity of the star is largest and the stellar spectrum is shifted bluewards. At the same time O sees the stellar position shifted maximally. Half a period later the position shift is in the opposite direction and the recession velocity shifts the spectrum redwards. •

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A new instrument HARPS (High Accuracy Radial velocity Planet Search), constructed by the Observatoire de Genève in cooperation with ESO, has been installed at the 3.6-m telescope at La Silla4). With its 1 m/sec accuracy it should be able to detect planets with 20 earth masses at 1 AU from a star like the Sun. However, earth-like planets could not be detected with this instrument. The mass of the earth is 314 times smaller than that of Jupiter or 329 000 times less than that of the Sun. With the earth’s orbital speed 30 km/sec, the reflex speed of the Sun is only 0.09 m/sec. Even if we were able to measure such a small speed, turbulent motions in the stellar atmosphere would tend to obscure the signal. A planet with a mass of only 14 earth masses was very recently detected with HARPS though at less than 1 AU from the star (Figure XV, 2). It should be noted that all quoted masses are minimum values because of projection effects, although in most cases they should be rather close to the real value. The motion of the star will also cause a displacement of its image on the sky. If our solar system were observed from a distance of 30 light years, the amplitude of the displacement of the Sun due to Jupiter would be 0.5 milliarcsec and that due to the earth some 0.3 microarcsec. Since the angular displacement would be inversely proportional to the distance of the star, only relatively nearby systems could produce detectable motions. With the VLT Interferometer (chapter VII) a precision of some 10 microarcsec in a stellar position should be attainable. Since the displacement is also proportional to the star-planet distance, the VLTI has excellent prospects of inferring major planets in planetary systems like our own. Also the ESA GAIA mission (Chapter VIII) should be able to discover numerous Jupiters in the general neighborhood of the Sun. Earth-like planets would be out of its reach. NASA is developing SIM – the Space Interferometry Mission5), which should reach

Figure XV, 2. The radial velocity curve of the star μ Arae indicates the presence of a planet in a circular orbit with a minimum mass of 14 earth masses. Based on observations with HARPS at the 3.6-m telescope at La Silla, it constitutes one of the smallest planetary masses detected to-date.2)

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microarcsec precision and so be able to infer earth-like planets around stars very close to the Sun. There are only a few stars near enough and so success depends on earth-like planets being sufficiently frequent.

Occultations When a planet passes in front of a star, it occults part of its light. The radius of Jupiter is about ten times smaller than that of the Sun, and so the fraction of the light intercepted is about 1%, which is rather easy to detect. However, the occultation is seen by us only when the line of sight to the star is more or less in the orbital plane of the planet. The probability of this being the case is rather small, of the order of the ratio of the radius of the star to the star-planet distance, and so only a few instances are known. In three of these the periodic variation in the speed of the star was first found from the radial velocity variations. This allowed the orbit to be determined and if the orbital plane had the right inclination the moment of occultation to be predicted. The prediction exactly fitted the observation, confirming that the velocity variations are really due to a planet and not to some ill understood effect of motions in the atmosphere of the star. Recently radial velocity variations were detected with the VLT in a faint star6) where an occultation had been suspected previously. In fact, the occultation coincided precisely with the moment when the radial velocity showed the planet to be in front of the star. The earth is 11 times smaller than Jupiter, and so an earth-like planet would take away only of the order of 0.01% of the star light. This is too small to be detected from the ground because of small fluctuations in the atmospheric transmission. However, in space this is no problem. A mission by the French Space Agency (CNES), with a major contribution from ESA, named COROT7), should be able to carry out very accurate stellar photometry. Launch is foreseen for 2006. Part of its mission will be to measure stellar oscillations (asteroseismology) in selected stars to gain information on their internal structure. In addition, it will observe 12 000 stars during 150 days in each of five fields of 4 square degrees, for a total of 60 000 stars, to look for occultations by planets. With its 27-cm telescope it should be able to detect earth-like planets around stars somewhat smaller than the Sun. However, its 150 day observing periods are too short to detect such planets at 1 AU from such a star, since at least three idential occultations are needed to be sure that planetary transits are observed rather than some erratic stellar variability. As a result, the orbital periods will have to be less than 75 days, and such planets will be close to the star and therefore quite hot. Since the required orientation of the orbital plane of the planets occurs so seldom, the number of detections will remain rather small. A much more ambitious mission of the same type as COROT has been proposed for the ESA program. “Eddington”8) would be composed of three parallel 70-cm telescopes with a field of view of 7 square degrees. During its

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first two years it would obtain asteroseismological data for some 50 000 stars in a number of fields and subsequently for more than three years continuously observe a rich field of stars. With the three telescopes stellar colors may be obtained. With the three year duration of the planet finding phase, planets like the earth in the “habitable zone” may be detected. Unfortunately, Eddington has been taken out of the ESA program because of financial problems. The habitable zone in the solar system is the domain where liquid water may occur. Inside the orbit of the earth temperatures would become higher and a planet may lose its water into space, as has happened on Venus. Further out water is frozen, as occurred on Mars, except perhaps during early days in the life of the planet. Thus, there is a rather narrow zone that could be hospitable to life as we know it. Of course, there are also other factors affecting the habitability of a planet, like its mass. Also elsewhere space missions have been developed for asteroseismology and the detection of occultations by planets. The first was MOST, a Canadian microsatellite launched in 2003, with a 15-cm telescope essentially restricted to asteroseismology9). The next one will be Kepler10), a NASA mission scheduled for launch in 2007. Kepler will have a 95-cm telescope, a field of view of 100 square degrees and a camera with of the order of 100 million pixels. It will observe some 100 000 stars during a four year mission. This is said to potentially yield a harvest of more than a hundred earth-like planets in or near the habitable zone. In Table XV, 1 are indicated the relative merits of the radial velocity, astrometric and occultation methods for finding planets. It appears that the Table XV, 1. The detectability of planets by different methods around a Sun-like star. The columns from left to right columns give the orbital radius R in AU, orbital period P in years, the reflex velocity of the Sun Vsun in m/sec, the amplitude of the angular displacement θ in microarcseconds if at 30 light years distance, and the relative dip ΔI/I in % of light intensity of the Sun due to the Earth, Jupiter and three imaginary planets placed at various distances. The last column gives the chance in % that the orbital planes are in the right orientation for an occultation to occur. Realistic observational limits during the coming decade are likely to be 1 m/sec, 1 μas and for the photometry well below 0.01 but depending on the stellar brightness.

Earth Jupiter “earth” “jupiter” “earth”

R (AU)

P (yr)

Vsun (m/s)

θ (μas)

ΔI/I (%)

Chance (%)

1.0 5.2 0.1 0.1 5.2

1.00 12.0 0.03 0.03 12.0

0.09 12.50 0.30 90.00 0.04

0.30 540.00 0.03 10.00 1.70

0.009 1.100 0.009 1.100 0.009

0.50 0.09 5.00 5.00 0.09

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radial velocity searches tend to detect massive planets close to the parent star, that the astrometric methods favor massive planets far from the star, and that the photometric measures are most likely to discover larger planets close to the star. Realistic observational limits during the coming decade should be 1 m/sec and 1 μas. The occultation data pose no insurmountable problem of precision, but, of course, the probabilities of a favorable inclination of the orbital plane are low.

Imaging Of course, it would be far preferable to observe the planet directly. Unfortunately, this is difficult owing to the proximity of the faint planet to a star of much greater brightness. In Figure XV, 3 are indicated the brightness of the Sun, Jupiter and the earth as seen from a distance of 15 light years. In visible light the Sun would be 1000 million times brighter than the earth. In the infrared the situation improves, but even at 15 μm the factor remains some 2,000,000. And the angular distance to the luminous source would be only 0.22 arcsec for the earth or 1”14 for Jupiter. In principle, the angular resolution of HST would be sufficient, at least for the latter. With a fully effective adaptive optics system also OWL would be

Figure XV, 3. The brightness of the Sun, Jupiter and Earth at different wavelengths when placed at a distance of 15 light years. Since at visible wavelengths the Sun is 109 times brighter than the earth, it would be difficult to detect the latter. In the infrared at 10 μm the situation is somewhat more favorable.

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able to see such an earth-like planet and even would have the sensitivity to take a visual-near IR spectrum. But light from the star scattered in the optics or in the atmosphere might be a problem. Moreover, the most interesting spectral features are probably in the mid-IR. Interferometry may provide the answer to such problems. In a typical interferometer the light is made to interfere positively so that the object is seen with the best angular resolution. However, in a “nulling interferometer” the optics are arranged differently so that at the center the interference is destructive and, as a result, there is a black spot. In this way the stellar light may be very much reduced. ESO and ESA are collaborating to develop such a nulling interferometer at Paranal to try out the technique and to attempt to detect exo-Jupiters directly. In the second decade of this century “Darwin” (Figure XV, 4) is planned by ESA. It would be an interferometer of maybe six 1.5-m telescopes flying in formation and operating in the IR11). If an earth-like planet was detected, its spectrum would give information about the composition

Figure XV, 4. Artist’s impression of ESA’s Darwin mission. Six 1.5-m telescopes on independent spacecraft send light beams to a central laboratory where they are combined to form a “nulling interferometer” which suppresses the light from the star. The spacecraft fly in formation with their relative positions controlled to a fraction of a wavelength by ion propulsion units.

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of its atmosphere. In particular the molecules CH4 (methane), CO2, H2O and O3 (ozone) could be looked for (Figure XV, 5). Ozone formation requires oxygen, and it is believed that abundant oxygen implies the presence of at least bacterial life. The earth’s oxygen would rapidly disappear by oxydative processes if oxygen production stopped. Methane is more ambiguous, since abiogenic processes may also produce it. The zodiacal light – scattered or emitted by dust particles in our solar system is likely to be a limiting factor in the detection and spectroscopic analysis of planets. It creates a diffuse glow which makes it difficult to see the planets. Calculations show that this would limit the detection of ozone to earth-like planets nearer than about 10 light years. The solution might be to send the telescopes of Darwin to an orbit much further away from the Sun. Current models of the zodiacal dust distribution suggest that Darwin at about the same distance as Jupiter would be able to detect ozone up to 60 light years away, which would yield more than a thousand stars where planet detection would be possible. Of course, such a project would also become much more complex and costly. An additional problem could be the zodiacal light in the exoplanetary system itself. The current interferometric studies from the ground may give an indication of how serious this is. Also some spectroscopic information about the planetary surface may be obtained. If such a planet has continents and oceans with their different reflectivities, photometric variations would result from rotation. NASA is planning a mission similar to Darwin, the “Terrestrial Planet Finder”, and current plans

Figure XV, 5. The spectra of Venus, Earth and Mars. In contrast to the other two, Earth shows strong absorption due to water (H2O) and ozone (O3).

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are to explore the possibility of combining the two missions. For ESA it could then be a “flexi mission”, a mission with a cap of around 200 M€ , although this seems an optimistic figure. Evidently Darwin is only a first step in a long program. If a planet with oxygen and water is found, we would wish to know if there are continents with vegetation, if there are oceans, if there are seasonal changes and many other things. That will take more than Darwin can provide. Larger telescopes and larger separations between them are required to have the sensitivity and the angular resolution to answer such questions. If any space science project could capture the imagination of the citizens in Europe, it would be this.

XVI. Publications

Since verbal science has no final end Since life is short, and obstacles impend Let central facts be picked and firmly fixed The Panchatantra1)

Articles in scientific journals constitute the most direct product of the astronomical research activity. Unless the scientific community is aware of what has been done, it is not possible to take the next step in the construction of our understanding of the physical world. Future research is organized on the basis of what is already known. Once that research has been completed, it will be reported in the journals allowing new programs to be developed, and so on. Of course, all of this is too schematic: many tracks are followed in parallel and many new investigations begin before the data of the previous ones have been published. But to allow progress it is necessary to have a repository of all previously obtained knowledge. If we did not, we would repeat what has been done before rather than use it as a stepping stone for further progress. But certain results are more reliable than others. So it is necessary to not only publish the results, but complete articles that also describe how they are obtained. As a consequence, the more than ten thousand practitioners of the astronomical sciences publish annually some 75,000 pages of printed text in the international journals. Of course, no scientist can read all of these 75,000 pages. So their contents are summarized in reviews or books and discussed in conference proceedings, in the latter case in part before they are published in journals. But if one really needs to know in detail how a particular result was obtained, there is no alternative but to read it in one of the journals. Modern informatics have helped much in this. With the data bases at the Centre de Données Astronomiques de Strasbourg and the NASA Astrophysical Data

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System it has become easy to locate references to articles on a given subject or object. Since the original astronomical literature contains virtually all the results of the research activity, we shall not consider any further the secondary sources of information. If we wish to quantitatively study the astronomical literature and the contributions to it by different countries, it is necessary to define what constitutes astronomy or the astronomical sciences. Some would include the sun, but perhaps not planetary research. However, it hardly seems reasonable to exclude objects that in the past were certainly part of astronomy for the sole reason that space missions allow now a much more detailed study. Others would include the heliosphere and the interplanetary medium, but not the magnetosphere of the earth. However, the interaction between the solar wind and the magnetosphere takes place in a complex region which also contributes much to the understanding of the former. So we shall include in situ observations of the transition region and the upper magnetosphere by spacecraft, but leave aurorae, the ionosphere and adjacent lower magnetosphere, magnetic storms observed on the ground and the quasi-steady part of the earth’s magnetic field to the geophysicists. The boundary between physics and astronomy is equally fluid. Where does particle physics end and the study of the early Universe or of dark matter begin? We shall exclude all particle physics in the laboratory or with cosmicray beams in the astmosphere, but include the study of the origin, acceleration, composition and propagation of cosmic rays in the Galaxy. Observations of neutrinos from the Sun and beyond, as well as searches for dark matter also belong to astronomy. It would hardly be reasonable to include all of General Relativity, but the astrophysics of black holes and the detection of gravitational waves from cosmic sources certainly are part of astronomy. Space experiments in fundamental physics, as for example the test of the “principle of equivalence”, are more ambiguous in character. However, pragmatically we include it since the technology is the same as that for the detection of gravitational waves; in the ESA program it serves as a technology demonstrator for the latter. Of course, this discussion shows the impossibility to have neat boundaries in an interdisciplinary subject. In practice, the matter is less complex because authors select the journals in which they publish, and as a result almost all articles in one particular journal tend to be entirely within or without the subject. The main exceptions occur in some geophysical journals.

The Astronomical Journals Four non profit journals dominate the field: “Astronomy & Astrophysics” (A&A), published by ESO on behalf of a (continental) European board under contract with a semi-commercial publisher, the “Monthly Notices

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of the Royal Astronomical Society” (MNRAS) of the UK, the “Astrophysical Journal” with its supplements (ApJ) and the “Astronomical Journal” (AJ) of the American Astronomical Society. These four account for some 84% of the publication volume in the astronomical sciences in the EU and US. In addition, there are to be considered the “Journal of Geophysical Research” (JGR) and the “Geophysical Research Letters” (GRL), both published by the American Geophysical Society. These contain sections on the planetary systems, the heliosphere and the earth’s magnetosphere in addition to more strictly earth-science related topics. The much smaller “Publications of the Astronomical Society of the Pacific” contain original articles in astronomy, but also some reviews and other matters. The American journals are partly financed by “page charges”, paid by the institutions to which the authors belong, and partly by the income derived from the subscribers. In principle, the page charges cover the costs of refereeing, editing and layout. The “Monthly Notices” derives all its income from subscriptions, “Astronomy and Astrophysics” most of it from subscriptions except that the governments of the participating countries subsidize the editorial offices, and a small amount of page charge income is derived from authors in other countries. Not surprisingly, the cost of a subscription to the European journals is higher (at least for libraries) than that of the American ones, as it covers a larger fraction of the total cost. A&A was created in 1969 by the merger of several national journals in Europe. Around the middle of this century the impact of the national journals had become much more limited in part because some were published in German or French. Initially, some authors continued to publish in A&A in these languages, which remained permitted under the conditions of the merger. However, authors wanted to be read and by now the journal is, in practice, entirely in English. Whether one likes it or not, English has taken over the role of Latin as a universal means of scientific communication. Fears that this will affect the survival of the other languages seem highly exaggerated. The scientific community is only a small subset of society and the dangers to other languages from popular “culture”, television, etc. are infinitely greater than those from scientific papers written in English. The scientific enterprise is by definition international and needs a common language. In middle Europe, the Czech journal has recently also been merged into A&A, while the Polish “Acta Astronomica” still survives. A new journal “Baltic Astronomy” was created some years ago. It remains to be seen whether this was a good idea. After all, the Estonians who publish mainly in the international journals are well known, perhaps more so than their brethren to the south. The Russians continue to publish several journals in Russian, but English editions of these are also available. They also make more and more use of the international journals. Japan and China have national journals, in English and Chinese respectively, but are increasingly publishing in the international ones; the Indian journal “Astrophysics and Astronomy”

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has undergone a steady shrinkage. It is clear that scientists everywhere want their best results published where they will have the greatest impact. But deprived of the best papers, the national journals fight a losing battle for an audience. An increasing number of frequently more specialized journals produced by commercial publishers completes the picture. These include from Kluwer (now Springer) “Solar Physics”, “Experimental Astronomy”, “Celestial Mechanics”, “Earth, Moon and Planets” and “Astrophysics and Space Science”, the last three containing also conference proceedings. From Elsevier there are “Icarus” (planets), “Astroparticle Physics”, “Planetary and Space Science” (including some conference proceedings), and “New Astronomy”. Wiley-VCH has recently revived the venerable “Astronomische Nachrichten” in part also with conference proceedings. In the following we shall only consider the original papers. Finally, there are “Nature” and “Science” which are high profile weeklies covering all the sciences. Also astronomical papers appear occasionally in physics journals. Because quantitatively the number is relatively small, and since the boundary between physics and astronomy is fluid, we shall not consider these further. In compensation, in the astronomical literature there also appear articles reporting results in atomic physics and other areas which, it could be argued, do not belong to astronomy as such. All of the international research journals have a strict refereeing system: every paper is evaluated by one or more anonymous expert referees as to its suitability for publication. Because of the time this process and the subsequent editing take, many scientists used to send out preprints of their papers. These have now been largely superseded by the “Astro-ph”, a web site which allows papers to be posted electronically. There is no refereeing, though really cranky papers are kept out. While this system is very fast, it may create problems in fast moving fields with issues of priority. It is all too easy to quickly send out a first version of a paper to a journal and to Astro-ph and subsequently refine or correct it if needed. The different journals have different page contents which also have varied over time. In the further discussion we shall normalize to pages with a content of 7000 characters per page, including also the empty spaces between words or at the end of a paragraph. While this puts the different journals on the same basis as far as printed text is concerned, there may remain some differences in page content associated with the layout of figures, photographs and tables. During recent years the situation has become more complex, because some of this material is presented only electronically or deposited in centralized archives. How much of this would have been published in print in the past is difficult to evaluate, since there now is less economic pressure to present it in compact form. In Table XVI, 1 we have listed the journals which in 2002 contained more than 1000 normalized pages of original research in astronomy. It is

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Table XVI, 1. The international journals containing more than 1000 normalized pages (7000 ch/p) reporting original research in the astronomical sciences during 2002. Subsequent columns give the name, the number of pages for the countries of the EU, the US and the whole world. The last two lines give the sum of the eight smaller journals and the totals. All figures have been rounded to the nearest multiple ten.

EU Astronomy & Astrophysics Monthly Notices RAS Astrophysical Journal Astronomical Journal Pub. Astron. Soc. Pacific Solar Physics Icarus J. Geoph. Res., Geo. Res. Let. 8 smaller Total

13380 8060 3960 720 100 410 780 870 1590 29870

US 610 1430 17670 5090 840 450 1880 1940 490 30400

Total 17450 12310 26430 7130 1120 1400 3110 3370 3430 75750

curious to see that even though most papers are submitted electronically, there remains a relatively strong tendency for the European and US communities to send their papers to journals edited locally. While this is understandable for the Europeans, who frequently have difficulties in paying the page charges, the phenomenon is actually strongest in the US. Taking into account that “Icarus” is published by Academic Press, now part of Elsevier, but still US based, we see that only 10% of US pages are published outside the country versus 22% of European papers published in the US.

Productivity of the European Countries To investigate the astronomical productivity of the different countries, we could count the number of pages published by researchers based in those countries. Since close to half of the papers published by Europeans involve authors from different countries, the simplest procedure is to allocate the papers to the country of the first author. It is not always clear that this is correct. When authors have made equal contributions, they are frequently listed alphabetically. However, statistically this should average out, unless the alphabetical distribution of names is different in different countries. Actually, such an effect exists. For example, Italian names tend to begin more frequently with a letter in the first half of the alphabet. However, the final effect on our statistics should not be more than a few percent. Based on counts of all the pages published during 2002 in the journals of Table XVI, 1, the results collected in Table XVI, 2 have been obtained.

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Of course, these numbers do not contain much information and they have to be considered with reference to other quantities. Here we shall refer them to the number of inhabitants or to the GDP of the various countries (Figure XVI, 1). The great productivity in astronomy of the UK and the Netherlands is in evidence, while also Finland and Sweden do well – though here the statistical basis of the result is more limited. Austria has low productivity; the same is true for Greece and Spain, though here it seems more associated with a low per capita GDP. The low values of Eire, Norway and Portugal, though of poor statistical accuracy, are also noteworthy. In the case of Norway it may be partly related to a concentration of their efforts on auroral and ionospheric research, while Portugal appears to be in the early stages of a rapid increase following its adhesion to ESO and ESA, and the appointment of a number of young researchers. In Table XVI, 2 the numbers of pages in the international journals for the countries of middle Europe are indicated, where it has to be taken into account that the Polish “Acta Astronomica” and the largely Lithuanian “Baltic Astronomy” are not included. The former would add 207 pages to the number for Poland, the latter 106 for Lithuania. However, these journals include much material that would be published only electronically in the typical international journals. Though the statistics are rather limited, it is encouraging that Czech (24 p./M inhabitants), Estonia (81 p./M inh), Hungary (18 p./M inh) Table XVI, 2. Normalized pages (7000 ch/p) published during 2002 in all the astronomical sciences as defined in the text in the journals listed in Table XVI, 1. Data are given for the EU (2002) countries (including here also Iceland, Norway and Switzerland) and for the countries of middle Europe that have become members of the European Union or may do so in the near future. Page numbers marked with an asterisk are for countries with important local journals (see text). For Eastern Europe and Japan see note 2.

Pages F D I UK A B DK SF GR

Pages

4027 5363 4636 8028 279 612 331 543 448

Ic Ei NL N P ESP S CH EU 29863

Pages

21 110 1836 120 176 1848 848 628

Bul Cro Cz Est Hun Lith PL Ser Slvk Slvn US 30408

68* 51* 247* 114* 178* 16* 655* 52* 71* 8

Publications

F

D

I

UK

A

B

DK

259

SF

GR

NL

ESP

S

CH

1

0,8

0,6

0,4

0,2

0

-0,2

-0,4

-0,6

-0,8

Figure XVI, 1. Astronomy pages per inhabitant ■ and per unit GDP ❑. Plotted are the fractional differences with respect to the EU average of 77 standardized (7000 ch/p) pages per Minh and of 4.4 pages per G€ of GDP. The corresponding values for Eire –0.61/–0.55, Norway –0.62/–0.70 and Portugal –0.77/–0.66 have not been plotted, since their statistical significance is low. On the same scale the US would be at 0.43/–0.23, the latter figure fluctuating with the exchange rate, as it is also the case, but to a lesser degree, for the EU countries outside the euro zone.

and Poland (17 p./M inh) already exceed the 14 p./M inh of the EU some 26 years earlier. This and the evidence of growth augur well for the future. The situation in these countries will be further discussed in the next chapter. Next we turn to the evolution of publication rates with time. Our earlier studies of data for 1976, 1987, 1992 and 1997 were based on more limited samplings of typically 4–6 months worth of the first seven journals in Table XVI, 1 supplemented by “Planetary and Space Science”. In 2002 these journals accounted for 92–93% of the EU and US production, and so their evolution should be representative of the total. In Figure XVI, 2 the resulting growth rates over the 12.5 year period from the average of 1987 and 1992 to 2002 are presented, while for the larger countries, the EU and the US the detailed evolution is shown in Figure XVI, 3. The figures illustrate the enormous increase in astronomical publications over the last 26 years, a factor of 2.7 for the US and 5.6 for the EU. In 1976 the EU published half as much as the US; by 1997 equality was reached.

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F

D

I

UK

A

B

DK

SF

GR

NL

ESP

S

CH

EU

US

2,5

2

1,5

1

0,5

Figure XVI, 2. Growth in pages determined from 2 p (2002)/[p (1987) + p (1992)]. Pages are from the first seven journals in Table XVI, 1, and also include Planetary and Space Science. The open bars are of lower statistical significance. Eire, Norway and Portugal have all increased, but the numbers of pages are too small for a meaningful result.

From data assembled by the US National Science Foundation3) it is seen that the total number of papers in all sciences in peer reviewed journals increased by 3.7%/y for W. Europe and by 0.9%/y for the US during the period 1988 to 2001. The corresponding growth rates in astronomy from Figure XVI, 3 are 5.0%/y and 2.6%/y for the EU and the US respectively. So in both regions astronomy publications were increasing at a faster rate than publications in all sciences. The overall publication volume in the EU in 2001 exceeded that in the US by 14%, while in astronomy equality between the two has prevailed since the mid-nineties. The increased access to state-of-the-art instrumentation played a major role in the European advances. In 1992 Germany launched the ROSAT X-ray satellite. Five years later some 300 ROSAT related papers, corresponding to 2000 pages, were published during the year. Even though not all of these had first authors in Germany, this easily explains the peak in 1997. The same appears to have happened in Italy, where the launch of Beppo SAX in 1996 led to an accelerated publishing activity some five years later. The UK has a particularly vibrant, competitive astronomical community, well integrated with their US counterparts and, as a result, have had access to a wide variety of instrumentation. One only has to look at the effective use they have made of the

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Number of pages published annually

8000

6000

F D I UK NL

4000

ESP EU/3 US/3

2000

0 1977

1982

1987

1992

1997

2002

Year

Figure XVI, 3. Evolution of the number of pages published annually in the journals of the first seven lines of Table XVI, 1 + Planetary and Space Science in some countries, the EU (2002) and the US. The data points are for 1976, 1987, 1992, 1997 and 2002. The lines are linear interpolations.

X-ray satellites Newton-XMM and Chandra launched by ESA respectively NASA in 1999. France did well in the beginning, but has slowed a bit. Employment practices have prevented the effective use of postdocs, while the early hiring waves have had the consequence that by 2002 nearly 40% of the permanent researchers were within 10 years of retirement. Of all EU countries, Spain has had the fastest growth. Once the government began to fund research more amply, a substantial inflow of young, active researchers and increased availability of instrumentation led to enhanced publishing activity. Nevertheless, in comparison with the other large countries it remains low, undoubtedly due to its lower per capita GDP and R&D spending. In 1998 its R&D was still below that of the Netherlands,

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although its population was 2.5 times larger. The Dutch started out very high in the European astronomy publication picture, owing to their early prominence in radio astronomical instrumentation, and as a result have not increased all that much thereafter, though Figure XVI, 1 shows that they still are close to the top in publications per capita. The situation in most other countries is apparent from Figures XVI, 1 and 2, though the statistical fluctuations from year to year are relatively large. We next turn to the subjects of the articles. From the 2002 data it appears that 14% of the astronomical publications in the EU dealt with the solar system (including the Sun), while in the US the corresponding figure was 21%, not surprising because of the large NASA program of in situ missions. The details for the EU countries are exhibited in Figure XVI, 4; of course, for the smaller countries the year to year variations are far from negligible. In 1997 a more detailed analysis of the numbers of pages in different astronomical research areas had been made on the basis of samplings of the pages in the first seven journals of Table XVI, 1, augmented by Planetary and Space Science. In most journals only four months worth of data were sampled. Since the geophysical journals were not included, no reliable data on solar system research could be obtained. In Figure XVI, 5 the relative percentages of five research areas are shown for the EU and the US, and for the four largest EU countries separately. In these figures the similarity of the F

D

I

UK

A

B

DK SF

GR NL

N ESP

S

CH

EU

US

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0

Figure XVI, 4. The fraction of pages devoted to the Solar System in the journals listed in Table XVI, 1 in 2002. Open bars correspond to inadequate statistics.

Publications

Galaxies & Cosmology

Milky Way Galaxy

Intersellar Matter

263

Stars

Sun

0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0

Figure XVI, 5. Relative fractions of pages for five astronomical research areas in 1997. In each area the columns from left to right are the US, the EU, France, Germany, Italy and the UK.

distributions of research interests is almost more striking than the differences. The statistics for the other countries are too limited for accurate results, but Spain and Sweden appeared to concentrate their activities in the area of galaxies and cosmology, while Austria, Belgium and Switzerland were particularly concerned with stars and the Sun, and the Dutch with neutron stars and related high energy phenomena. However, the limited sampling may lead to large year to year variations. The 1997 data also showed that theoretical research accounted for 33% of the activity in the EU versus 25% in the US. Some 45% of EU publications involved international cooperation, versus 24% in the US. Of course, the lower value for the US reflects the size of the country. More than half of the cooperations of the EU countries involved at least two within the EU. So in many ways the “European Research Area” already exists in astronomy. While it is straightforward to determine the quantity of published material, it is far more difficult to make a judgment as to its quality. This has led to a simple minded “citation index” assuming that role. Increasingly it is being used by university administrators and research councils in decisions about appointments, promotions and funding. The “Institute for Scientific Information” in Philadelphia counts the number of times a paper is cited in other papers in a large number of

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journals. From this a citation index or an impact factor is constructed. The connection to quality then follows from the assumption that a larger number of citations indicates a higher quality. Trivial counterexamples may be given: an erroneous paper on a timely subject may have many citations simply to point out that it is wrong! But a more fundamental objection is that there is a strong sociological factor in citations. If one of my friends has written a paper, it gives both of us pleasure if I cite that paper. I shall be equally inclined to cite the friend’s students, since it is good for their career. The extremes that are possible in this respect are the “citation clubs” in the US, whose members agree to cite each other to improve their prospects or standing. In the US there is a tendency to believe that what is done in the Anglosaxon countries in general, and more specifically in the US, is particularly worthy of confidence and, therefore, of citation. Not surprisingly the US journals do well in their “impact factors”. Frequently it is not at all evident that the cited article has been read or made use of. In recent studies it was found that typographical errors in cited references propagate rapidly through the literature, presumably because people copy the citation4). All of this does not mean that the citation indices are totally without value. First of all, even though the number of citations is not very informative, their absence is. In addition, within well defined communities they may have some value. For example, if two scientists in an institute compete for a position in the same subject area and if they have written in the same journals, the relative numbers of citations may contain some information. As a basis for a judgment of the relative quality of the totality of the papers published on the two sides of the Atlantic, the canonical impact factors are totally irrelevant. In addition, there have been more trivial, but serious errors in the citation indices. The journal Astronomy and Astrophysics was normally referred to as Astron. Astrophys. However, gradually the abbreviation A&A has been taken over, which was not recognized by the ISI software. As a result, the “impact factor” of the journal for 2000 was listed as 2.36, but following complaints corrected to 4.355). Similar problems occurred in other years. Some university administrations in Europe count publications of candidates for professorships multiplying the numbers for low impact journals by 0.5. So young European scientists who published in the European journal A&A, to which various governments make a contribution, were set back compared to their colleagues who published in non European journals for which payment was required. In several cases irreparable harm was done to careers. All of this shows again the dangers of both the belief that quality can be quantified in simple ways and in leaving it to commercial enterprises to determine scientific quality.

XVII. European Astronomy: Researchers and Funding

Fundamental science cannot be driven by institutional, industrial, governmental or military pressure. This is the reason why I decided as far as possible not to accept money from Government. C.V. Raman1)

Europe spends less on R&D as a proportion of its GDP (1.9%) than either the US (2.8%) or Japan (3.0%). In parallel with this there are also fewer researchers per capita, 2.2% in the EU versus 3.5% and 4.4% in the US and Japan respectively. These figures of course are totals of all types of research performed by very different actors: pure or applied research and government or private industry. As noted by R. May2), if only science base (universities, government funded laboratories, etc.) spending is compared, the situation is more favorable with EU, US, Japan spending 0.65%, 0.63% and 0.85% of GDP respectively, the difference with the other figures being accounted for by larger Development spending. It is also true, however, that in large pure science projects industrial development plays an important role. The development of mirror materials has much benefitted the VLT, detector development has been essential to photon detection on the ground and in space; in fact, much of industrial development for the military has benefitted the construction of satellites for space research. So the overall R&D deficit in Europe still has a negative effect also on “pure” research. EU governments talk much about the “knowledge economy” and about the need to improve education at all levels, but when it comes to budget time this is all too easily forgotten. Especially during the last decade a generalized pessimism seems to have set in that has had a paralyzing effect on research and education. This has been particularly visible in the budgets for space research. Both ESA and national space science budgets have tended to decline during the last decade in real value, amounting now in

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total to less than 20% of those on the other side of the Atlantic. In ground based astronomy the situation is more favorable, but much effort will be needed to maintain the rough equality that has been achieved. How much does Europe spend on the astronomical sciences and how many astronomers are there? Since essentially all funding comes from governments, one could have thought that such questions would be easy to answer. Nothing is farther from the truth. Some countries have only a very nebulous idea on their astronomical personnel or spending. This is partly due to the fact that at universities funding may not have very clear destinations as far as disciplines go. Moreover, in some countries universities are dealt with at the provincial rather than the national level. Another factor is that funding for organizations like ESA and ESO passes through different ministries in different countries: education, foreign affairs and even economics ministries. Finally there is pure sloppiness: as an example, one country reported to ESA a figure of 500 space scientists working there in 1994 and 300 in 1996. One wonders what disaster befell the 200 missing ones! Even more mysterious is the increase from 400 to 1107 over a two year period in another country. So, even official figures may have to be carefully analyzed or corrected. In this chapter we shall analyze the staffing and funding for astronomy in various countries. As in the previous chapter I define “astronomy” as including all studies of objects outside the magnetopause of the earth. It should be remembered that others frequently use more restrictive definitions. However, I have difficulty in seeing that exoplanets and stellar winds belong to the subject, while the planets in the solar system and the solar wind do not. Moreover, there is a substantial overlap in funding and personnel, especially in ESA and in the national space programs. In addition, there is the question: what is a researcher? Are PhD students working on their thesis to be counted as researchers? We shall do so. Are astronomers building instruments scientists, but engineers doing the same not? We include the former who also frequently use the instruments later on, but not the “pure” engineers, i.e. specialists in mechanical, optical or electronic engineering, though the distinction between the two is not always evident. Of course, engineers and technicians working on astronomical projects are included in the funding figures. Because of outsourcing, the numbers of technical and administrative personnel have become less significant, but the overall cost figure is. In some countries the retirement age is low, but many researchers remain active, though not included in the statistics; in others scientists may be counted to a high age. Some scientists work nominally part time, though in reality they do more. Others have moved permanently or temporarily into administrative positions. In the US some scientists have created small enterprises which perform research sponsored by the government. Some scientists work in industry, while remaining active researchers. Hence, it is clear that statistics of astronomical personnel will always remain of limited accuracy.

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Relatively detailed information is available for the four major countries in European astronomy. France every so often has a “colloque de prospective” and Germany a “Denkschrift”, the most recent ones both in 2003. In Italy rather detailed data are available as a result of governmental plans for restructuring, and in the UK the Particle Physics and Astronomy Research Council regularly provides information on its spending plans. The central funding sources are easier to analyze than the regional or provincial ones, which in some countries assume increasing importance. European Union funding may suffer from fluctuations. A relatively large contribution may also be made by many universities in which there is astronomical personnel without there being a formal astronomy department or institute. It is not always easy to discover such cases. In the smaller countries the situation is even more varied. The Netherlands have regular planning exercises with good documentary material, while Spain also recently made an excellent analysis. Easily accessible and complete data are lacking in several countries. So the estimates have more uncertainty. Upon request several persons have tried to collect the necessary data in their country; these form the basis of the corresponding data in this chapter; nevertheless, they had to be modified in some cases to correct for different definitions of “astronomy”. There also is a recent joint brochure of the European Science Foundation and the European Astronomical Society entitled “European Survey of National Priorities in Astronomy”. Though its intent is laudable, it is unfortunately very short on specifics and quantitative information.

Staffing Few countries in Europe have done much rational planning in hiring astronomers. In some years governmental policies were favorable and relatively numerous researchers could be engaged, while at other times the opposite happened. This has had several negative consequences. If in some years many recent PhD’s are hired, the average quality will be lowered. But in the years of scarcity they cannot wait without employment and so even very good PhD’s will leave the field, frequently forever. Thus, if one wishes to retain the best students, a relatively stable inflow would be preferable. However, from the point of view of a director of an institute, it is impossible not to use the opportunity of hiring some new staff: if the favorable years are not fully utilized, one is likely to get even fewer positions in the bad years. Favorable and unfavorable periods tend to have durations of several years or even decades. In countries where life time employment laws prevail, this has the consequence that the age distribution of researchers may have important hills and valleys. While many researchers remain active to a high age, it is, nevertheless, true that flexibility decreases with age and that for

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the scientific liveliness of an institute an important fraction of young researchers bringing in new ideas is essential. Two different philosophies occur. In countries like France the inflow into PhD programs has been set at such a level that an important fraction of the PhDs can find employment in the astronomical area, while post doctoral jobs of limited duration are only accepted under very specific conditions. The situation in Italy has been rather similar but is beginning to change. In other countries, like the UK, the inflow into PhD programs is much larger, many PhDs obtain positions as “post docs” for a few years at a time, and only a small number can obtain permanent employment in the field. The latter system has definite advantages. A continuous rejuvenation takes place, competition for the permanent jobs stimulates activity, and the selection process is much less open to error, since a judgment on the suitability of candidates for a permanent position is based on a substantial number of years of research production rather than just on the PhD. A negative aspect may be that it may lead to risk aversion. For a post doc to engage in a long term project that may not lead to results is dangerous. From a social point of view the situation is more ambiguous. Having an army of post docs, many beyond forty years of age, looking every few years for new positions in different universities, creates problems in particular for researchers with families. However, if there are enough possibilities to find employment outside the astronomical field, it is a question of personal choice. For example, in the Netherlands more than two thirds of the PhDs in astronomy find jobs in informatics, governmental planning agencies and even in banks and insurance companies. Also quite a few are leaving the country to find positions elsewhere. However, if most PhDs cannot remain in the field, there should be a certain obligation for the universities to ensure that the education is sufficiently broad so that the transition to the outside world is facilitated. In practice, this is rarely considered. Furthermore, prospective PhD students should be informed very clearly about the prospective employment situation. In all of this there is, of course, also an economic aspect. In most countries PhD students work for little money, and so they represent a low cost work force which makes a major contribution to the analysis of the data stream that comes from ever more prolific instruments. To a lesser extent the same is also true for the post docs. It is no accident that the UK is at the top of the publication rate per unit GDP. Also in Germany the number of PhD students and post docs has increased rapidly. Here, however, the educational system has tended to cause the average age for the award of the PhD to be relatively high. At the same time, the employment laws make it difficult to continue giving non permanent jobs to people in their forties. More and more EU countries recruit PhD students and post docs without regard to nationality. This has many positive aspects. The pool of young talent is increased, and it could be anticipated that the more mobile researchers tend to be also the more imaginative. Here also the EU commission makes a contribution

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in funding various internationalization programs. And, of course, this also fosters European integration and the creation of a “European Research Area”, so eloquently fostered by the EU commissioner Ph. Busquin. In Table XVII, 1 we have assembled the available information on researchers in Europe. Subsequent columns give our estimates for the number of researchers with PhD and of PhD students, the percentage this represents of all researchers in the countries and the number of pages published (from Table XVII, 1. Astronomical researchers in various countries. The columns from left to right give our estimates of the number of post PhD scientists and of graduate PhD students, the percentage of both of these of all researchers (R&D), the pages published per researcher, and the number of astronomers per million inhabitants. Thereafter follow the numbers of IAU members in 2004 and their average annual growth rate over the period 1992–2004. While the IAU numbers are subject to certain selection effects (seniority, underrepresentation planetologists) they are exact in contrast to the numbers of scientists which are subject to uncertainties. EU refers to the pre-2004 membership plus Norway and Switzerland. Values for Sci + PhD st for Belgium and Norway have been obtained by multiplying IAU with 1.9, the average EU ratio.

Country

Sci

F D I UK

800 850 950 800

A B Dk SF Gr Ic Ei NL N P ESP S CH EU US

% PhD st all res.

IAU

IAU/M + %/ inh yr

0.65 0.58 1.39 0.91

4.0 4.0 4.4 6.2

17 16 18 22

633* 492* 443* 582*

11 6 8 10

1.0 1.1 1.4 1.6

50

0.78 (0.83) 0.35 0.72 2.0 0.44 0.72 0.65 (0.26) 0.56 0.86 0.50 0.72

2.8 (3.2) 5.7 4.5 2.8 4.2 1.8 9.0 (2.9) 2.7 4.1 5.0 5.2

12 (19) 11 23 15 18 16 13 (9) 7 11 19 14

34* 101* 59* 54* 105* 4* 35* 153* 22* 35* 245* 108* 89*

4 10 11 10 10 14 9 10 5 4 6 12 12

1.3 1.9 1.4 5.3 1.4 2.4 2.5 0.9 0.8 6.7 3.6 2.1 4.1

0.71 0.56

4.9 5.6

16 20

3219* 2457*

8 8

1.6 1.4

(191) 13 46 30 1 28 80

(42) 65 315 133 100 70 100 55 4200 4500

ast/M inh

200 500 100 500

50 45 75 130 4 32 125

p/ast

1900 (900)

* 25 estimated ESA personnel deducted.

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Table XIV, 2) per astronomical researcher. In the table we have not made a distinction between tenured (permanent) scientists and others. For the long term health of the subject a reasonable balance between the two is necessary. In quite a few places the average age of the tenured scientists is excessively high with the risk that only part of these positions will be retained by the universities. Situations differ considerably as a function of national policies in the matter. But some illustrative examples show the problem: in the two main Danish universities 15 out of 20 tenured scientists are above 55 years of age, at the university of Lund all but one. Most professional astronomers are members of the International Astronomical Union (IAU). Such membership is free of charge, the IAU being financed by contributions from national academies and equivalent bodies. Usually, researchers become members shortly after their PhD. The numbers of IAU members as a measure of the astronomical research population, given in the fifth column of Table XVII, 1, have the advantage of being very precise and to refer to people who consider themselves “astronomers”. However, planetary and magnetospheric scientists tend to be underrepresented, while retired members without research activity may retain membership. New members are elected every three years. In the right hand column is the mean annual growth rate of the number of IAU members for the period 1992–2004. It should be noted that the growth is showing signs of leveling off. Annual growth during the six year period 1986–1992 was still 3.6%/yr; in France the number was even 10 less in 2004 than in 2001, the first decline in Europe. Inspecting Table XVII, 1, we see the similarity in the numbers of astronomers per million inhabitants in France, Germany and Italy, with the UK being particularly research and astronomer friendly. Italy has a high fraction of astronomy researchers, but its total researcher population is low. Among the smaller countries, Norway, Portugal and Spain are low in the number of astronomers, as they were in publication rates, though the latter two appear to be improving rapidly.

Funding While it is not easy to determine the number of researchers with precision, it is still harder to determine the number of euros spent by different countries on astronomical activities. One component, however, is known precisely: the contributions to ESA and ESO, which in 2003 amounted to 361 and 100 M€, respectively corresponding on average to 0.048 and 0.015% of GDP, respectively, for their member countries. Alternatively stated, the two account for some 36% of all EU funding for astronomy. If we add to this an estimate of the funds spent by the countries on payloads for ESA and instruments built for the VLT, the total ESA/ESO related annual expenditure becomes of the order of 540 M€ per year. This means that some 42% of the

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total astronomy spending has been “europeanized”, i.e. its content is largely decided by Europe-wide decisions, even though, of course, a national consensus is also needed. Again, the “European Research Area” is seen to exist already in the astronomical sciences. This calculation is based on the fact that during the nineties the sum spent on payloads for ESA amounted to 24% of the annual contributions according to information provided by the member countries. Undoubtedly, this has diminished in the meantime. We have adopted an uncertain 20% for 2003. For the VLT instruments we estimate member country contributions at some 5 M€ /year. To ascertain the national spending in astronomy, a more detailed analysis of sometimes rather fragmentary data is needed. The results are to be found in Table XVII, 2, where the cost per astronomical researcher (from Table XVII, 2. Estimated European funding for astronomical research in 2003. The columns from left to right give the contributions to ESA/ESO and the estimated total spending in M€ , the part of GDP spent on astronomy in %, the costs per astronomical researcher and per page published both in k€. Figures in parentheses are particularly uncertain estimates.

ESA/ESO M€ F D I UK A B Dk SF Gr Ic Ei NL N P ESP S CH EU

77.1 107.9 63.7 83.9 8.3* 13.9 9.1 5.1** 0 0 3.5* 22.4 6.3* 5.4 25.3* 12.7 16.9 461

Total M€ 240 285 225 210 19 (33) 17 16 8 0.3 8 55 (11) (9) 70 29 43 1280

% GDP

per ast (k€)

per page (k€)

0.15 0.13 0.17 0.13

240 211 214 162

60 53 49 26

0.08 (0.12) 0.09 0.11 0.05 0.03 0.06 0.12 (0.06) (0.07) 0.09 0.11 0.15

190 (173) 293 132 50 60 133 268 (262) (138) 156 172 277

68 (54) 51 29 18 14 73 30 (83) (51) 38 34 68

0.13

210

43

* Only ESA. ** From mid-2004 + 1.9 ESO.

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Table XVII, 1) and per page of research results (from Table XV, 2) is also given. The figures have been based on information provided by scientists in the various countries or on more official documents, except where given in parentheses when they are my very crude estimates. In most cases, with regard to both the definition of “astronomy” and the items included, I have made adjustments to bring them as much as possible on a common basis. Thus, the values tend to be somewhat higher than those given by countries with more parochial definitions of astronomy where the subject (except for the Sun) begins only beyond the orbit of Pluto.

Middle and Eastern Europe Ten countries have joined the European Union in 2004. Several others are expected to do so later in this decade. Economic circumstances are harsh, currencies have fluctuated and many researchers spend a significant part of their time abroad to gain access to advanced equipment or to improve their finances. None of these countries are members of ESO or ESA. For several countries realistic statistics are not easy to come by. So here we shall restrict ourselves to two easily available data, the number of IAU members and the publication data from Table XVI, 2 assembled in Table XVII, 3. Data are given for the four countries with more than 100 pages in 2002. The other countries have too large statistical fluctuations and their data has been added together. From the Table it is clear that the numbers of astronomers are still on the low side and that the same is the case for the productivity. However, the Table XVII, 3. IAU members (2004), annual growth rate over last 6 years, IAU per million inhabitants, pages (Table XVI, 2) per IAU and the fraction of all researchers who are IAU members, for four countries, for all other Middle European countries with astronomical activities, compared to data for W. Europe.

Czechia Estonia Hungary Poland Other M. Eu All M. Eu W. Europe

IAU 74 23 45 128 192 462 3219

%/yr 0.7 0.7 1.6 1.5 1.5 1.3 1.5

IAU/M inh 7.2 15 4.5 3.3 3.9 4.0 8.3

p/IAU 3.3 5.0 4.0 5.1* 1.8 3.2 9.3

IAU/all res. 0.00 59 0.00 40 0.00 24 0.00 37

* Poland publishes a national journal “Acta Astronomica”; so productivity may be slightly underestimated.

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fraction of all researchers that are astronomers is on average the same as in the West. So it reflects an overall weakness in the research activity, related to the still low GDP/capita. In 2003 GDP/capita in the most favorable case, Czech, amounted to 7400 €, compared to the W. European average of 25,000 €. Since in the period 1995–2003 the ratio of the GDP of Cz + Hun + PL to that of W. Europe increased by 5% per year, it may be expected that also the research activity will slowly improve. At this rate in 25 years equality would be reached. While this may seem very far into the future, the planning horizon for the large future projects in astronomy we are considering also extends into the third decade of the present century. So it would be reasonable to include the Middle European countries in our planning exercises now. Russia with 377 and the Ukraine with 162 IAU members are still rather low with 2.6 respectively 3.2 IAU/M inh. The 6 yr annual growth rate in IAU is 1.5 respectively 5.3%/yr. Productivity seems low with 3.4 respectively 2.3 pages/IAU. However, here it has to be taken into account that at least one high quality regional journal serves these countries. So the true productivity is well above these figures. With a large population of well educated physical scientists remaining, a rapid growth could be expected, once the economy improves, provided the governments retain their interest in pure science.

Why pay for astronomical research? Why should governments support astronomical studies? When in 1768 the Royal Society wrote a memorandum to King George III requesting funding for the Cook expedition to observe the transit of Venus in front of the Sun and thereby to infer the Sun-Earth distance, they listed three grounds for such support3): it would avance knowledge, it would contribute to the solution of an important practical problem, and it would enhance national prestige. The first item has moved many a king, government or philantropist, frequently in conjuction with the third one. One only has to look at the evidence from Tycho’s observatory on Hven (Dk) or at the well preserved remains of the observatory of Jai Singh at Jaipur (India) to realize that sometimes a non negligible part of GNP was devoted to an enterprise whose sole purpose was to advance knowledge. Today many remain convinced that increasing our understanding of the Universe is a worthy aim. Also national prestige has played a large role: the “race” to the moon and the visits to other planets were very much motivated by this. The solution of an important practical problem in Cook’s time was the determination of the position at sea. The Global Positioning Systems have now solved this problem, but in their development there is an important astronomical heritage. A few more current examples may also be mentioned.

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The study of the Sun has certainly a direct societal importance. Solar flares which cause storms in the solar wind have an impact on radio communications, on satellite performance, and even on electricity grids. A better predictability of such events would be useful. Also, solar variability and perhaps the solar wind have an effect on terrestrial climate. Their detailed study is necessary to ascertain the precise role of human activities in global warming. Asteroids or comets are sometimes in orbits where they may hit the earth. The great extinction at the end of the Cretaceous (extinction of dinosaurs and many others) was caused by such an event. In 1909 the very much smaller Tunguska object destroyed a 40 km diameter forest area in Siberia. Had it struck a few hours later, it could have destroyed an urban area in Europe. Discovery of dangerous objects and consideration of remedial measures, therefore, have some importance. Some scientists believe that valuable minerals may be mined in asteroids or perhaps the moon. While at the present cost of space transport this seems far fetched, it could be a motive for further study. Mars is the planet most like earth, but is currently hostile to life because of its tenuous atmosphere and low temperatures. It has been suggested that the introduction of highly effective greenhouse gases could raise the temperature and evaporate frozen CO2 and water; this could possibly make the planet suitable for plant life and later even for humans. Some people have proposed to colonize Mars so that if disaster befalls earth, humanity could continue. Again, by stretching probabilities a bit, the study of Mars could be considered “useful”. Such practical or semipractical reasons to support astronomy could be and have been advanced. However, the principal reasons are others. We wish to know the nature of the Universe we live in, its origin and its future. We wish to know where we came from, if there are planets like ours, if there is life elsewhere and, if so, its similarities or dissimilarities with life here. And the general progress of science requires progress in all of its domains. Much of progress in physics, for example, has come about by interaction with astronomy, and the tie between the two has become stronger in recent times. Finally, societies that make advances in science make progress in technology and vice versa. This is not only because technological progress depends on an understanding of physics, but also because the mind set that is propitious to progress in science is the same as the one that leads to advances in technology and the construction of a rational society. The same point has been made in purely financial terms in a study carried out by the Bureau d’Economie Théorique et Appliquée (Strasbourg)4) in which the indirect economic effects of ESA’s programs were evaluated. It was found that direct ESA payments of 3901 MAU to industrial firms had generated indirect benefits to these firms of 12677 MAU, or a return coefficient of 3.25, confirming an earlier study which had yielded a coefficient

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of 2.9. The most important contributions to these spin-offs were made by “technological effects” (sale of products designed for ESA and diversification thereof) and “work related effects” – the increased capabilities of design and production teams. While these figures refer to ESA’s overall program, the fact that the science program contributes particularly effectively to innovation within ESA makes these figures important in the science context. While one may be convinced that funding for the sciences, including astronomy, is justified, this does not tell one yet at what level this should be. Four factors have to be considered: past commitments and levels of support, equilibrium with adjoining sciences, interest to an educated public, and international competition. The first point is obvious. If an institute exists or a project has been started, it is difficult to suddenly terminate it. Apart from contractual aspects with regard to personnel or to industry and other suppliers, it would be wasteful. If, for example, ESO funding would have ceased just before completion of the first telescope of the VLT, a large sum of money would have been spent, but nothing useful would have been achieved. A certain continuity is necessary. Also too sudden increases in funding have dangers: neither the intellectual nor the administrative infrastructure may exist to effectively utilize the funds. In some European countries available positions for young scientists have fluctuated wildly with several years of drought being followed by sudden abundance. During the years of drought brilliant students have come from the universities; no positions in the chosen field being available, they have taken other jobs to make a living. During the years of abundance there may not be enough top level students delivered by the universities and positions will be given to those with inadequate abilities for a scientific career. Both factors will lead to a lowering of the average level. However, while continuity is thus important, this does not mean that every scientific discipline should have a fixed fraction of the total funding. The promise of the field for innovation and fundamentally new results should very much influence its support. As an example, it is not at all surprising that the share of the biological sciences has increased in several countries, both in view of their intellectual promise and their potential utility for human welfare. For several decades science funding in Europe has gone up, and to privilege some areas could be done without taking much away from others. At present, overall funding has been stable or even diminishing in some countries, and frequently painful decisions are necessary. An example of an organization that has done this well is the Max-Planck-Gesellschaft in Germany which is responsible for the funding of more than fifty scientific institutes. To make room for new institutes in new fields of science, several existing institutes have been terminated. The alternative would have been an underfunding of all areas of science. An appropriate equilibrium with other adjoining branches of science is an important factor. Information about particle physics may be obtained

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from studies with accelerators on earth or from astrophysical studies. As a consequence, it would not be appropriate to put all funding in one or the other. Since many physicists will have an interest in both and may make proposals for funding in both, an equilibrium between the two may arise from the scientists themselves. Since the financial support for science comes through the political process, an appropriate role for the educated public cannot be denied. As many of the issues cannot be judged by non scientists, this role cannot be dominant, but it cannot be negligible either. For various reasons the public is motivated to support studies of the origin of the Universe, exoplanets, Mars, the origin of life, as well as of various diseases, ecology and global warming, to name just a few. In the US, where private philantropy has a long tradition, donations to such fields have made an important contribution. In Europe, where this is not so much the case, the governments have to take such factors into account. A corollary is that the scientists have a great necessity to explain what they are doing to a broader public than just to their colleagues. Finally, international competition plays an important role. There is no point in basic science in doing things that have been done elsewhere ten years earlier. So in the basic science areas that a country wishes to pursue, the funding has to be comparable to that in other countries. Of course, the different cost and salary levels have to be taken into account. Countries with limited financial possibilities have to be selective in what they are doing. For Europe the reference has been mainly the US. With 40–50% more population it has a smaller R&D work force overall (15% less) than the US, but spends about the same fraction of GNP on government sponsored R&D, however much less in total R&D. In astronomy the European spending is about half that in the US, mainly because of the much lower spending on space research. However, the number of astronomers per inhabitant is about 10% larger. As a consequence, the overall funding per astronomer is substantially lower in Europe.

XVIII. The Future

Then was not non-existent nor existent… Who verily knows and who can declare it, whence it was born and whence comes this creation? Rig Veda1)

During the last decade European astronomy has seen remarkable progress. In the radio domain MERLIN, EVN and IRAM, in the IR ISO, in the optical the VLT, in X-rays ROSAT, BeppoSAX and XMM-Newton, in soft γ-rays INTEGRAL, and in the hardest γ-rays HESS and MAGIC have allowed the coverage of nearly the complete electromagnetic spectrum. They have created opportunities for research equal to and not infrequently superior to the best available elsewhere in the world. In the solar system Cluster, Huygens, Rosetta and Mars Express represent unique facilities. The half shares in the equally unique Ulysses and SOHO and the 15% share in HST have been important assets to European scientists. The near future looks equally bright. ALMA will explore the submm Universe with unprecedented angular resolution and sensitivity. Herschel will study the adjacent wavelength region in the far IR which until now has been largely unexplored, and Planck will observe the Cosmic Microwave Background left over from the Big Bang over the whole sky with unmatched angular resolution. The VLT will be supplemented by two large telescopes in the northern hemisphere, the Spanish 10-m GRANTECAN on La Palma and the Germany/Italy half share of the LBT in Arizona. GAIA will observe distances and motions of a thousand million stars, 1% of all that exist in our Galaxy. Solar Orbiter will size up the Sun from close by. Venus Express will orbit the planet that has not seen a spacecraft for a decade, and B.Colombo Mercury. VIRGO, GEO-600 and LISA will be looking for gravitational waves. For all these facilities and for many others sophisticated auxiliary instruments have been or will be constructed.

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Spectacular discoveries have been made in Europe during the last decade. If I had to choose three, it would be the first ever exoplanet around a solar-type star, the resolution of the more than thirty year old mystery of gamma-ray bursts, and the definitive evidence for a black hole, and the precise measurement of its mass, in the center of our Galaxy. Others might select other items, since there is a long list of discoveries. It might be concluded that all is well and that European astronomy can continue to coast at its present level. This would mean to misunderstand the dynamics of science. What today is at the forefront of science, will be history tomorrow. The scientific results obtained with the current equipment will lead to the formulation of new problems which can only be solved by new, more powerful instruments. Moreover, the competition never sleeps. If Europe would stand still, its recently acquired high status would soon vanish. What at the moment is an instrument that is the envy of the world, may be ready for the museum when we or others will have built still more powerful instruments. If no up to date equipment can be constructed, the best scientists and engineers, who give the field its dynamics, will move elsewhere or to other fields of science. The major instruments with which today’s discoveries are being made have been conceived up to 2–3 decades ago and developed and funded during the decade preceding their completion. So now is the time to begin to think of the instruments for the 2015–2030 period. Of course, new scientific and technological developments will occur in the meantime. So we should not set plans for future instruments and missions in stone. If circumstances change drastically, we should be willing to scrap the plans we have made when these are no longer relevant. Nevertheless, long term planning is necessary to determine in which directions we should orientate our current efforts in both science and technology. So let us see what could be the projects in different areas that are just over the present European horizon. I would select the following four as particularly unique, timely, realistic and important: SKA, the Square Kilometer Array, in radio astronomy (Chapter IX); OWL, the 100-m Overwhelmingly Large Telescope, in the optical (Chapter VIII); XEUS, the large X-ray facility (Chapter XI); and Aurora, the Mars exploration program (Chapter XII). Two other projects would have equal importance but less evident realizability in the time frame considered: Darwin, the IR space interferometer in space (Chapter XV) with a broad range of aims, but in particular the discovery and study of earthlike planets, and Solar probe to in situ study the region where the solar wind has its origin. Since the money streams for ground and space based projects are still largely separate, we shall consider the two separately. But before this, we should see what are the principal science themes that we wish to study.

Science themes Notwithstanding the successes that have been achieved, the list of unsolved problems remains long. I see eight science themes to be at the center

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of current interest. Some of these may perhaps be solved during the coming two decades. The first five themes are of a fundamental nature in the sense that we are ignorant or uncertain about the basic physics involved. The last three are of great complexity – a bit akin to the study of the climate of the earth. Even if the basic physics were fully understood, the number of processes that need be studied is so large that progress is slow. In Table XVIII, 1 are summarized the themes and the instruments which may contribute to their elucidation. A brief description follows: 1. Dark Energy. Observations of the brightness of supernovae seem to indicate that the expansion of the Universe is accelerating with cosmic time, contrary to expectation. It had been assumed that gravity would lead to a deceleration. It is then said that this is due to some kind of repulsive “dark energy”. So far, the evidence depends on supernovae of type Ia with a redshift less than z = 2. To further investigate this it is necessary to observe supernovae (also of other types) at large redshifts. These would be so faint that telescopes like OWL are needed. 2. Dark Matter. In galaxies and clusters of galaxies there is much matter that generates gravity, but is otherwise unobservable. Its nature is unknown. At first it was thought that it could consist of low mass stars or gas at temperatures where little radiation is emitted. Observations with current optical and X-ray facilities indicate that this is not the case. More likely it is composed of neutralinos, axions or other particles beyond the “standard model” of particle physics. If so, the next accelerator at CERN, the LHC, may contribute evidence. Direct detection of dark matter has been attempted with particle detectors, but so far without result. It is also possible that dark matter particles and antiparticles annihilate. The resulting γ-rays might be detectable with instruments like HESS and MAGIC. 3. The Earliest Universe. Various lines of evidence suggest that there has been an early period of inflation, a very rapid expansion of the Table XVIII, 1. Principal Themes of Astronomical Research.

Theme

European Instruments most directly involved

Dark Matter Dark Energy Earliest Universe Black Holes Extreme Energy Cosmic-rays Galaxy / Star Formation Sun Life in Universe

HESS / MAGIC, particle detectors, LHC OWL Planck, Virgo? Virgo / LISA, XEUS, SKA… Auger, EUSO, neutrino detectors JWST, Herschel, OWL, ALMA, SKA… Solar Orbiter, Solar Probe Darwin, SKA

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Universe. The cause is unknown. Quantum fluctuations from still earlier epochs would have been the seeds from which much later galaxies and other structures in the Universe have formed. The imprint of such fluctuations has been detected by observations of the Cosmic Microwave Background. Planck and possibly observations of gravitational waves will give information on the very early epochs. 4. Black Holes and their immediate environment have been studied at radio, optical and X- and γ-ray wavelengths. The VLT has obtained particularly compelling data on the black hole at the center of our Galaxy. Much remains to be done with more powerful X-ray and radio instruments like XEUS, SKA and (space) VLBI. The most conclusive information might result from gravitational wave detectors like Virgo and LISA. 5. Extreme Energy Cosmic-rays. While we know that they exist, little is known about their characteristics. But their high energies show that they contain a message about extreme situations in the Universe, though because of their rarity we are still unable to decipher the message. Auger, EUSO and various neutrino detectors should contribute to our understanding of these remarkable events. 6. Galaxy and Star Formation. Much has been learned from observations with the VLT, ISO and IRAM and other radio telescopes. But sensitivity and angular resolution are inadequate to study the early stages of galaxy formation on more than the grossest features of star and planet formation. Also only a beginning has been made with the analysis of the evolution of the elemental composition and the chemistry of matter in galaxies and star forming regions. JWST, Herschel, OWL, ALMA, GAIA and SKA will open up this field which in the near future should benefit much from the VLTI. 7. The Sun remains an object of much interest because of its effect on the earth’s climate and environment. Only a start has been made with the study of the heating of the corona and the solar wind. The complexity of the processes involved in solar activity makes continuing observation at high spatial, spectral and time resolution a necessity. Following SOHO, Solar Orbiter and also ground based solar observations should contribute significantly to the field. 8. Life in the Universe. The discovery of exoplanets indicates that abodes for life may be widespread beyond the earth and possibly Mars. Evidently, the search for biological markers in the Universe is becoming a major activity. The Aurora program, project Darwin and SKA could make major contributions. These eight topics may be considered central themes in the exploration of the Universe. However, the large instruments that are most likely to address these themes will also make many other discoveries that will further complete our picture of the Universe – or perhaps change it radically. We now turn to some aspects of the instrumental projects beyond 2005.

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Ground based projects OWL is currently being studied at ESO as a 100-m optical, near IR telescope. According to present plans, first science operations with part of the primary mirror could begin in 2017 with full completion in 2021. The capital cost is estimated at 940 M€. A smaller 60-m version would cost perhaps half as much. Some industrial studies are at the basis of these estimates. More modest versions (20–40 m) have been studied in Sweden in cooperation with other countries. In the US plans are being made for a 30-m telescope at a capital cost of 400 MUS$. If we exclude the cost of interferometry, Paranal development and instrumentation, the cost of the VLT would have been around 260 M€ (2004 value). Thus, the extraordinary claim is that improved technology allows a 30-m to be built at the same cost as the 16-m equivalent VLT and the 100-m version of OWL for less than four times that! Even if these estimates were correct, the question is from where the financing is to come. Till 2011 ESO will invest some 30 M€/yr in ALMA. At the same rate some 300 M€ would be available by 2021. New member countries might add to the ESO budget some 10 M€/yr in investment money. In addition, European countries have invested some 200 M€ in telescope projects like LBT, GRANTECAN, VST, VISTA and others. So if funds of the same order of magnitude would be directed towards OWL, the total available on a decadal basis could be some 600 M€. The requirement for “new” funding would be brought down to 30–40 M€/yr for ten years. While in the present pessimistic economic mood any new money would be hard to come by, such a sum does not seem unattainable especially if the European Union would begin to distribute significant research funding as is under consideration. The main danger to OWL may be a lack of commitment in Europe. Here and there one hears that one should buy into a US project to obtain access to a large telescope more quickly. Obviously, if one or two countries would follow such a route, there might not be enough money left to participate in the European project. It is worth remembering that whatever harm may have been done to European astronomy by having to wait some eight years for the full VLT after the completion of the first Californian Keck telescope, has been more than compensated by the possession now of the world’s top telescope, with an enviable set of instruments. Certainly after this Europeans should not be content to become again the poor relation with limited access to someone else’s big telescope. Better to wait a while longer and then to leapfrog to the forefront. SKA is a very different story. With a large number of partners, who have a long tradition of cooperation, it is an ideal project for a worldwide collaboration. SKA is currently envisaged as an array of radio telescopes with a total collecting area of 1 km2, scattered over an area of perhaps 3000 km in diameter. The total cost has been capped at a thousand MUS$. By its very nature an array is particularly suitable as a cooperative project. Issues of industrial return are more easily solved, since there is no need to build all

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elements in the same industry. In a monolithic telescope it is more difficult to divide the roles, and if a partner cannot meet its commitments a catastrophic situation may arise. In an array one would redistribute the roles or make the project somewhat smaller. Radio astronomy in Europe has generally been financed on a rather fragmented basis. The only major international project has been IRAM with a French-German investment of some 60 M€. Actually it started out as a simple superposition of two national projects which were combined, since on a national basis money was available but no staff positions. Since the staff were then on the IRAM payroll, it did not count for the national personnel limits. Of much smaller financial size is the EVN center which coordinates the observations of the national telescopes of the European VLBI network. Current investments in European radio astronomy include a 64-m radio telescope in Italy, LOFAR in the Netherlands and a 40-m telescope in Spain, at a combined cost of more than 200 M€. In addition, several other countries have made significant investment in the radio domain. Hence, a total European investment in SKA of some 250–300 M€ over a 10–15 year period would not need to be prohibitive. However, the projects mentioned were all on the national territory. With SKA undoubtedly outside Europe, the funding might be more difficult to obtain. And, of course, with SKA and OWL occuring over the same time period does not help.

Space Projects XEUS has been proposed by a broad coalition of European high energy astrophysicists as their next project. A strong X-ray community in Europe has been built up in the past around the four projects in this area: EXOSAT, ROSAT, BeppoSAX and XMM-Newton. In addition, European scientists have been active participants in Japanese, Russian and US projects by contributing instruments. But XMM-Newton is expected to end its useful life not long after 2010, and it becomes important to consider its successor. XEUS should have an effective area of some 10 m2 and a sensitivity two orders of magnitude better than XMM. In addition, it should allow observations of hard X-rays up to around 50 keV and a much better spectral resolution. Cost would probably be in the 500–1000 M€ range. In the US there are plans for Constellation-X, an X-ray facility of four telescopes on four separate spacecraft, at a projected cost of 800 MUS$. Also in Japan an X-ray facility with emphasis on hard X-ray optics is under consideration. Perhaps a joint European-Japanese project would be an attractive option. For the moment, there would be no room in the ESA budget for XEUS before the later half of the second decade, but, of course, economic circumstances and ESA’s fortunes are hard to predict so long in advance. In any case too long a wait would be most damaging to what may well be the strongest space science community in Europe which has been built up with much effort and money. Aurora is the Mars exploration program that has been started within ESA as an optional program; every country decides how much it will

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contribute and receives a proportional amount of industrial return. Current funding is modest (2005–2006: 31 M€), with Italy and the UK contributing the most. The stated aim of Aurora is manned exploration by 2033. Obviously, precursor missions are needed. The present planning includes a rover on Mars by the end of the decade and a sample return mission later. Two years after the start of Aurora, the US announced a major initiative for exploration of the moon and Mars. Undoubtedly, as with the Space Station, there will be pressure on Europe to participate as a junior partner; as in that case, it is not clear that this would serve European interests.

Possible Space Projects Darwin is an ambitious project to detect earth-like planets and to analyze their spectra for evidence of life. It would be a large IR interferometer with perhaps six telescopes on independent spacecraft and two more spacecraft for a variety of necessary functions. In the US a similar project, the Terrestrial Planet Finder, is being studied. TPF is presented as a project for the next decade at a cost of 1700 MUS$. Discussions have taken place between ESA and NASA about a joint mission. However, even half of Darwin would be a major budgetary problem for ESA; if participation were much less than half, would it really be in Europe’s interest to participate? Solar Probe was one of the “green dreams” of Horizon 2000, 20 years ago, and reappeared with the same status in Horizon 2000 Plus. It would involve a spacecraft in a Ulysses-like orbit, but approaching the Sun within four solar radii to study the origin of the solar wind. Obviously, thermal problems are very severe at that distance. Also the probe would move so fast that it would pass through the critical region in less than a day. NASA considered such a project with two passes separated by five years but because of budgetary problems as yet nothing definite has happened. Evidently, these problems would be still more prohibitive in the ESA context. Of course, many other proposals have been made. How about travelling to Jupiter’s moon Europa to see whether there is an ocean under the frozen surface? Or even further afield, what about Neptune or a super Cluster-type mission or a super LISA? In judging such proposals one has to be aware that there is a fundamental difference between what is reasonable in the context of an ESA budget and that of a NASA budget. If one is rich, one can afford occasionally missions addressing issues of rather specialized interest. If not, one better concentrate on missions of interest to a broad community and at the center of current scientific activity.

International Collaborations International cooperation could play an important role in future large and small European projects. Until now, NASA has taken a prime place

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among ESA’s collaborations – in some cases like Huygens, HST and SOHO with very positive outcomes. A stronger diversification of partners would be very much in the European interest. It would better ensure the autonomy of the European program. Relations with Russia have developed in a very positive way. INTEGRAL is the prime example which followed the earlier French SIGMA collaboration in gamma-rays. Cluster II and Mars Express have been placed into orbit with Russian launchers, and a more general cooperation in the launcher area has been established. Also in Mars-96 an extensive participation of European scientists went very well, though unfortunately the mission failed at launch. It would seem particularly attractive to continue that collaboration in the framework of Aurora. Also Japan offers many possibilities for cooperation. It is a partner in the ESA Mercury mission and it made an effective contribution to ISO. In X-ray astronomy, both solar and beyond, Japan has established an enviable record. It could be a very suitable partner in XEUS. The UK has participated very successfully in several Japanese X-ray missions. ESA is participating in the X-ray mission ASTRO E2 by providing a ground station and is also gaining some access to ASTRO F in the IR. The possible future SPICA mission in the IR is also of much interest. China is making rapid progress in the space field as in other areas of science. China and ESA are already collaborating in the magnetospheric mission “Double Star”. Future collaboration could be particularly fruitful in the solar area where China has been considering a space telescope. Also India is developing a substantial X-ray/uv satellite for launch in 2007, while a lunar orbiter is planned for 2008. Discussions are taking place about a possible European instrumental contribution to the latter. The beginnings of an interest in space activities are also in evidence in Latin America. So it is clear that there are many possibilities for cooperative missions worldwide. Europe has much to offer in this respect. In space technology it has reached maturity and politically it imposes few constraints on its collaborations. The advantage has been illustrated by the case of “Double Star”. Because of US export regulations with their extraterritorial reach, some existing instruments had to be rebuilt in order to eliminate parts of US origin. With so much trouble created by the US side, Europe began to look like a more attractive partner. So, why not profit from that? A final point concerns the Space Station. At the time that European participation was decided, it was the usual scenario. The Germans wanted to join a US project, the French to advance the European launcher capacity. In practice, the German participation in Ariane was traded for a French participation in the Space Station. The apparent motive on the US side was even more interesting2): “part of Begg’s [the NASA Administrator] rationale for inviting European cooperation had been to forestall competition with NASA’s capability”. Many voices were raised at the time contesting the utility of the Space Station for research3).

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There were also warnings that the funding for the Space Station would squeeze funding for space research. In fact, Germany stated that it could not participate in Aurora because of the heavy expenses it still incurs for the Space Station4)! Fortunatly this decision has been reserved in 2005. Because of the large amount of money going into the Space Station, scientists have tried to think how to put it to some use at least. Examples are the ROSITA, Lobster-ISS (Chapter XI) and EUSO (Chapter XIV). So what does one hear now from the other side of the Atlantic? That the US Administration is eager to finish and close down by the next decade the Space Station and the shuttle. The new head of NASA could not have been more explicit: “It is beyond reason to believe that [the ISS] can help to fulfill any objectives, or set of objectives, for space exploration that would be worth the $ 60 billion remaining to be invested in the program”5). While one may agree with the statement, why did Europe let itself be dragged along at a cost of thousands of millions of euros in a profitless enterprise? The high cost and modest returns of Spacelab in the preceding decade should also have been a warning6). Hence, the conclusion is clear. International cooperation is a valuable asset, but Europe has to have clear aims and ensure that such cooperation fosters European interests. Moreover, partners should have unambiguous agreements and feel bound to their execution. As Bonnet and Manno7) wrote “For European scientists, the best partners are those for whom international cooperation represents a moral commitment, a way of behaving, and an irreplaceable asset.”

Organizational Issues Who will determine the future choices of large projets in Europe? A number of organizations could have a larger or smaller role: The International Astronomical Union, the Organization for Economic Cooperation and Development, the European Science Foundation, the European Astronomical Society, EU networks, ESA, ESO and a variety of national governmental bodies. Of course, the financial envelope within which the projects are realized is ultimately set by the national governments – individually and collectively. The IAU constitutes a global forum for the discussion of issues and possible cooperations. For example, the agreement of scientists in a number of countries to work together towards the financing and construction of SKA was concluded at the last triennial meeting of the IAU. But the IAU is barely able to scrape together a minimal budget for its administrative services, and it has neither the mission nor the structures needed to set priorities. The OECD through its Megascience Forum from time to time has held meetings with the aim to discuss possibilities of cooperation in or coordination of large science projects. While the aim is laudable, the impact has been limited. The major science agencies already have their channels through

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which they interact; an example is the Inter Agency Consultative Group of the four principal space agencies. Of course, in practice the direct contacts between these agencies may be even more important. As a consequence, they felt that there was little to be gained from the OECD initiatives. In fact, both ESA and NASA declined to participate in the 2003 Megascience Forum held in München. There are, however, some areas where the OECD may have a unique role to play. For example, major investments have been made by the OECD countries in radio astronomical facilities. With SKA on the horizon, these will be further increased. However, radio interference from telecommunications and other sources might very much reduce the value of these investments. It is entirely within the purview of the OECD to intervene with governments to see what can be done. In fact, it has already begun to do so. The ESF is an association of European research councils which has been effective in coordinating activities in areas of science where strong European organizations are lacking. Its role in organizing a cooperation to obtain a geological cross section of the continent or in ocean floor drilling projects has won high praise. However, there is little it can add to what ESA and ESO are doing. In the US every decade a report is made, under the auspices of the National Academy of Sciences, in which priorities are set for the next decade. Several European scientists have thought that such a report should also be framed in Europe, and that the ESF might be the organization to do this. However, some care is needed in simply taking over the procedure. In the very large projects, ESA and ESO between them cover some 90% of the subjects in the astronomical sciences in Europe. They have extensive and well functioning advisory structures, and their planning horizon extends for 10–20 years. Some of the countries have also their national plans which extend over a decade or more. Could an ESF planning exercise for the coming ten years be more than a superposition of the existing plans? Certainly it would be difficult for the ESF or another such body to contest the priorities of the national plans or those of ESA and ESO. A recent glossy brochure produced by ESF and EAS conjointly is hardly encouraging. The European Astronomical Society was founded in 1990 during a regional meeting of the IAU in Davos. From the beginning it was organized as a panEuropean entity, including West, Middle and Eastern European scientists. At the time there was some controversy as to whether it was to be a society of national societies or a society of members. In the former case, the governing council would have been composed of representatives of the national societies of which the Royal Astronomical Society in the UK and the Astronomische Gesellschaft in Germany are particularly strong. While initially these societies contested the need for a society of members – with the members fully controlling the society – during the subsequent decade positive relations have been developed. In particular the annual meeting of the EAS is organized conjointly with a national society, as a JENAM (Joint European National Astronomy Meeting), a format which has generally been rather

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successful. Nevertheless, it still has not quite found its role on the European scene. The comparison with the American Astronomical Society is quite striking. With an annual budget of some 8,000,000 $, it publishes two major journals, has an office with influence in Washington, engages in extensive educational activities and organizes meetings that few young PhDs looking for a job will fail to attend. The main problem is that the EAS came late in the day when other arrangements for publications had been made and national societies had their spheres of influence and patronage. ESA and ESO have been very successful in combining the scientific quality, technical feasibility and financial viability of their projects within the limits set by governmental financial limits. They have largely avoided having committees that discuss all the great science one could think of, without considering the technical and financial aspects. With the ST/ECF they have created a structure that contributes to the effective interaction between the two, although perhaps more could be done in this respect. Both have an organizational setup with a top layer of governmental representatives (including scientists), and below this an ample scientific advisory structure which also ensures a sufficient level of communication with the scientific community at large. Whatever other initiatives may be taken, it is important that the system be preserved which has served European astronomers so well. As the Americans would say: “If it ain’t broke, don’t fix it”. It is sometimes said that ESA and ESO serve only part of the astronomical sciences. This book shows that this is only very partly true. The effective roles of ESO in ALMA and of ESA in the area of fundamental physics in space show that most subjects are covered. For the few that are not, effective solutions have been found. RadioNet with some modest support of the European Commission is a case in point. In fact, there are now several EU related and partly EC funded networks. RadioNet will conduct joint activities on interferometric software, phased arrays and mm-wave technology. In addition, it organizes the transnational access program for European radio facilities and provides some funds for trips to such facilities. RadioNet currently receives 2.5 M€ annually from the EU. OPTICON is another EC funded network. It deals in particular with ELTs, the extremely large telescopes. OPTICON started out at a time when the UK was not a member of ESO. Now that the UK has joined and that it also seems likely that Spain will do so in the coming years, one should wonder if there really is an advantage in having such a structure outside ESO, which could easily lead to more division. In addition, OPTICON organizes its transnational access program for medium sized optical telescopes and a number of Joint Research Activities, including uv astronomy, interferometry and astronomical technology. Current EC funding appears to be of the order of 4 M€ per year. A new network ILIAS, involving some 70 laboratories, focusses on astroparticle physics and gravitational waves.

XIX. Epilogue

…entre européens depuis l’Atlantique jusqu’à l’Oural. Charles de Gaulle1)

In this book I have tried to show that European astronomy is in excellent shape and that it has the full potential to remain so during the coming decade. With a slightly increased financial envelope for ground based facilities and a more substantial increase for space research this should also continue thereafter, provided careful choices are made between the desirable and the feasible. A largely autonomous European program appears to be possible, but suitably selected international cooperation can very much enrich it. Of course, individual scientists will continue to collaborate worldwide, as they have done in the past. I have described only superficially what others are doing to provide the backdrop for European developments. Others have amply described the world from their point of view. One last point should still be made. The European Union has recently acquired ten new member states, and some others are likely to join by the end of the decade. As a corollary it follows that we have to see how to integrate these countries in the European scientific organizations, both for their benefit and for ours. Sometimes one hears that these countries will dilute the observing time or the mission opportunities without contributing much to enlarging the financial envelope for European astronomy. Interestingly, one is also told that the data flow of the new instruments is so high that there are not enough scientists to deal with it. Since several of the countries in question have well educated scientists, one problem may solve the other. Furthermore, while several W. European economies are stagnating, in middle Europe quite a few have high rates of growth. So even if one did not have a sense of collegiality for one’s fellow European scientists, one should welcome these countries because in the future their contributions will become more significant.

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With increasing membership, adjustments will have to be made to the way in which scientific organizations function. It is impossible to give the same powers of decision to countries who pay 0.1% of the budget as to those with 10%. Since already some steps have been taken in the direction of increased voting weight for the larger countries in the W. European scientific organizations, this should not lead to too much trouble. After all, the European Union is facing the same problem in a more acute way and is considering solutions. Ultimately, it would be natural to also include Eastern Europe in the overall European framework. Russia and the Ukraine have many excellent physicists and astronomers and much experience in space matters. Their space industry continues to function well. In fact, some discussions are taking place between Russia and ESA about a closer association. Obviously, there are many problems to be resolved. But is it too much to dream of the day when pan-European scientific organizations foster research on the continent, create a scientific center for peaceful research second to none and collaborate on a basis of equality with others who have the same aim?

Notes

Introduction 1)

ESO, Garching, 1991. Harvard University Press, 1994. 3) Kluwer Academic Publishers, 2001. 2)

Chapter I 1)

Pliny the Elder, Natural History, Book II, 55. A few foundations in Europe are the exception: For example, the VolkswagenStiftung has made some important contributions to the cost of radio telescopes, while also the Carlsberg Foundation in Denmark and the Wallenberg Foundation in Sweden made contributions. While important, the total of these and other such contributions represents a very small part of astronomical investments in Europe. 3) G.E. Hale, The Possibilities of Large Telescopes, Harper’s Magazine 15, 639, 1928. 2)

Chapter II 1)

C. Darwin, The Voyage of the Beagle. F. Hoyle, Home is where the wind blows, Univ. Science Books, Mill Valley, California, 1994. 3) H. Siedentopf (ESO Bulletin 1, 11, 1966) found on 3 sites in South Africa 1285–1750 clear hours, to be compared with in Chile 2300 at Tololo and 2760 near Copiapo. 4) Derived from data in A. Blaauw, ESO’s Early History, ESO, 1991. 5) A. Blaauw, l.c., p. 157 states without further comment that it was used only in radio telescopes and in the design of the 6-m of the USSR, while C. Fehrenbach (Des hommes, des télescopes, des étoiles, éd. du CNRS, 1990, p. 435) writes that such a design presents many difficulties and is only interesting for telescopes larger than 5 m. Another reason that more revolutionary designs were not considered may be related to the fact that decisions were in the hands of the “Instrumentation Committee” (IC), composed of senior astronomers well versed in optics, but less conversant with developments in mechanical engineering and control concepts. A similar conservatism may be noted in the rejection by the IC of Strewinski’s more daring design of the Schmidt telescope (Blaauw, l.c., p. 192). 2)

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6)

A. Blaauw, l.c., p. 166. A. Blaauw, l.c., p. 240. 8) Just as an example, at the last moment in 1974, the cooks had been moved up a notch because an incompetent cook could poison people, and the night assistants because an incompetent one might destroy a telescope. After having had three “Heads of Personnel” at ESO, I left the post vacant, since that took the smallest amount of my own time. Evidently after the VLT project led to a major expansion, this was no longer possible. 9) The building was designed by the architects Fehling and Gogel who made a remarkably imaginative design. While staying within the unit costs of German university type buildings, they managed to have a huge entrance hall that gave the building its identity. During the construction the building company went bankrupt, but through the rapid intervention of the German government delays were minimized. In September 1980 the Geneva establishment of ESO was transferred to the new headquarters, which were inaugurated by the President of Germany on 5 May 1981. The proceedings of the accompanying symposium “Evolution in the Universe” were published by ESO in 1982, edited by P.O. Lindblad and L. Woltjer. 7)

Chapter III 1)

Ovidius, Ars Amatoria, 26. R.J. Weyman, N.P. Carlton, The Multiple Mirror Telescope Project, Sky and Telescope 44, 159, 1972. 3) A. Labeyrie, Stellar Interferometry Methods, Annual Reviews of Astronomy and Astrophysics 16, 77, 1978. 4) M.J. Disney, Optical Arrays, Monthly Notices Royal Astronomical Society 160, 213, 1972. 5) L. Woltjer, The Case for Large Optical Telescopes, in ESO Conference “Optical Telescopes of the Future”, ed. F. Pacini, W. Richter, R.N. Wilson, p. 5, 1978. 6) R.N. Wilson, The Messenger (ESO), 29, 24, 1982. 7) R.N. Wilson, Reflecting Telescope Optics II, chapter 3.5, Springer Verlag Berlin, 1999; The History and Development of the ESO Active Optics System, The Messenger (ESO), 113, 2, 2003. 2)

Chapter IV 1)

A till then unknown common spirit which could almost be considered political, has developed an organisation which aims to reach a scientifically entirely new level. O. Heckmann, Sterne, Kosmos, Weltmodelle, R. Piper & Co. Verlag, München 1976. 2) Proceedings of the Workshop on ESO’s Very Large Telescope, ed. J.P. Swings and K. Kjär, ESO 1983. 3) P. Léna, Aperture Synthesis in the Infrared: Prospects for a VLT, ibidem p. 129. 4) F. Roddier, Future Possibilities of Ground-based Interferometry in the Visible, ibidem p. 135. 5) R.N. Wilson, Reflecting Optical Telescopes II, ch. 3.3.5, Springer-Verlag, 1999. 6) D.E. Enard, ESO 16 Metre Very Large Telescope: The Linear Array Concept, in IAU Colloquium 79, Very Large Telescopes, their Instrumentation and Programs, ed. M.-H. Ulrich, K. Kjär, ESO 1984, p. 767.

Notes

293

Chapter V; Most notes refer to documents of ESO Council and Finance Committee. Many other facts can be found in the ESO Annual Reports 1)

J. Conrad, Heart of Darkness. Cou-403, 1988. 3) Cou-457, 1991. 4) FC-833, 1989. 5) Cou-448, 1991. 6) Cou-443, 1990. 7) Cou-413, 1988. 8) Cou-433, 1990. 9) Cou-434, 1990. 10) Cou-528, 1994. 11) Cou-578, 1995. 12) Cou-453, 1991. 13) Cou-403, 1988. 14) Cou-429, 1989; see also Cou-458, 1992. 15) For a general description of Chilean astronomy, see L. Bronfman, ESO Messenger, 107, 14-18, 2002. 16) O. Heckmann, Sterne, Kosmos, Weltmodelle, pp. 300-301, Deutscher Taschenbuch Verlag, München, 1980. 17) Cou-521, 1994. 18) Cou-613, 1996. 19) Cou-570, 1994. 2)

Chapter VI 1) 2)

3)

4)

5)

I. Newton, Optiks. C. Piazzi Smyth. The Friday evening discourses in Physical Sciences at the Royal Institution 1851–1939, Astronomy volume 1, 16; edited by B. Lovell, Elsevier publ. 1970. Surveys had been made in the Peleponesos and in Spain. Much importance was attached by the Director, Prof. W. Elsässer, to a European continental site, to avoid possibly increasing air fares. Ironically touristic developments have had the consequence that air fares to the Canaries are particularly low. Also the French had studied a site closer to the Spanish coast, some 50 km SW of Calar Alto, and found it to be unsatisfactory, though better than sites in France (R. Cayrel in ESO Conference Proc. 18, 45, 1983). C.G. Abbot, Annals Smithsonian Institution 6, 6, 1942. In Smithsonian Miscellaneous Collections 101, No 12, Abbot presents data for a number of sites, including Mt. Brukkaros in Namibia, which show that even in the most favorable month 6 mm of H2O was present at 1600 m altitude. In the northern hemisphere a 2600 m high summit near the St. Katherine monastery in the Sinai was found to be the best site; it was operated from 1934–37 when fear of war led to its abandonment. The annual mean precipitable water vapor was 2.5 mm, corresponding to a median value as low as Paranal. It might be interesting to investigate the area more closely. A. von Humboldt; see L.A. McIntyre “Die Amerikanische Reise”, p. 258, GEO Verlag 1982.

294

6)

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P.C. Keenan, S. Pinto, H. Alvarez. The Chilean National Observatory (1852-1965), Universidad de Chile 1985. 7) Information Bulletin for the Southern Hemisphere, 12, 29, 1968; H.W. Duerbeck et al., ESO Messenger 95, 34, 1999 8) J. Stock, Science 148, 1054, 1965. 9) H. Siedentopf (ESO Bulletin, 1, 11, 1966) found sites in S. Africa with 1285–1750 clear night hours to be compared with for Tololo and Copiapo 2300 respectively 2760 hours. Image quality at Tololo was “distinctly better” than for the S. African sites. 10) A. Blaauw, ESO’s Early History, ESO, 1992, p. 44, even though later the opposite was stated, pp. 47/48. While after the coup d’état in 1973 political relations between Chile and Europe became rather cool, it would have been politically more difficult to operate an observatory in S. Africa. 11) Ibidem, pp. 56-62. 12) Major coups occurred in 1891, 1924, 1931/32 and 1973; see S. Villalobos et al., Historia de Chile, Editorial Universitaria, Santiago 1974. 13) J. Stock. Astronomical Observing Conditions in Northern Chile, ESO Bulletin 5, 38-40, 1968. 14) Information Bulletin for the Southern Hemisphere 18, 19, 1971. 15) Ibidem, 10, 20, 1967. 16) According to J.W. Warner (Pub. Ast. Soc. Pacific 89, 724, 1977) 6% of time at Chacaltaya had less than 1 mm H2O against 16% at Mauna Kea, the latter being 1200 m lower. Less than 3 mm occurred 50% of time against 83% at Mauna Kea. At Chacaltaya median cloud cover was about 50%. According to the data for the station of the Smithsonian Institution near Arequipa, Peru, presented by G.P. Kuiper (Lunar and Planetary Laboratory Communication 156, Univ. of Arizona), the average of the median monthly cloudiness there during day time is 44%. So there seems to be no advantage to go northward beyond the Chilean border. 17) I have given a description of the expedition in ESO Messenger 64, 5, 1991, following a first account in Site Testing for the VLT in Northern Chile, ESO Conference Proc. 18, 147, 1983. 18) A. Ardeberg, in Very Large Telescopes, their Instrumentation and Programs (IAU Coll. 79), ed. M.-H. Ulrich & K. Kjär, ESO, p. 417, 1984. 19) In the Paranal area Sarazin also made seeing measurements at Co Armazoni (3060 m), some 20 km east of Paranal, and Co La Montura, a few km to the north. The former was found to be very similar to Paranal, the latter slightly worse (VLT Report 62, VLT Site Selection Working Group, ed. M. Sarazin, 1990). 20) R. Kurz, S. Guilloteau, P. Shaver, The Atacama Large Millimetre Array, ESO Messenger, 107, 7, 2002. 21) M. Sarazin at ESO web site on astronomical climate. 22) F.P. Chavez et al., From Anchovies to Sardines and Back: Multidecadal Change in the Pacific Ocean, Science 299, 217, 2003. 23) E.K. Duursma, Rainfall, Riverflow and Temperature profile trends; Consequences for Water Resources, Heineken NV, Amsterdam 2002, p. 24. 24) M. Grenon, ESO internal report. 25) L. Núñez, M. Grosjean, I. Cartajena, Human Occupations and Climate Change in the Puna de Atacama, Chile, Science, 298, 821, 2002. 26) M. Sarazin, F. Roddier, The ESO differential image motion monitor, Astronomy & Astrophysics 227, 294, 1990.

Notes

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27)

E. Carrasco, R. Avila, A. Carramiñana, Pub. Ast. Soc. Pacific 117, 104, 2005. For this, the Asian sites and the South Pole, see Astronomical Society of the Pacific Conference Series 266, 2002. 29) C. Muñoz-Tuñón et al., New Astronomy Rev. 42, 409, 1998, give a (~ 1 year) mean value of the seeing of 0”75 for these subsites, to be compared with 0”80 as the long term mean for Paranal. 30) M.R. Kidger, New Astronomy Rev. 42, 537, 1998. 31) A. Jabiri et al., Astronomy & Astrophysics Suppl. 147, 271, 2000, give a 14 year average 1984–1998 of photometric nights for La Palma. 32) J.S. Lawrence et al., Nature 431, 278, 2004. 33) D. Hofstadt, personal communication 2004. 34) S. Barrientos, Regionalización Sísmica de Chile; thesis Universidad de Chile, 1980. 28)

Chapter VII 1)

Thomas Mann, Doktor Faustus, Fischer Verlag 1967, p. 361. The data of the cosmic creation are nothing but an anaesthetizing bombardment of our intelligence with numbers, endowed with a comet tail of two dozen zeros which pretend to have still something to do with measure or reason. 2) R. Arsenault et al., ESO Messenger 115, 11, 2004. 3) R. Arsenault et al., ESO Messenger 112, 7, 2003. 4) T. Ott et al., ESO Messenger 111, 1, 2003; R. Genzel et al., Nature 425, 934, 2003. 5) A. Glindemann et al., ESO Messenger 98, 2, 1999. 6) Ch. Leinert et al., ESO Messenger 112, 13, 2003. 7) A. Richichi & R.G. Petrov, ESO Messenger 116, 2, 2004. 8) W. Jaffe et al., Nature 429, 47, 2004. 9) K. Kuijken et al., ESO Messenger 110, 15, 2002. 10) J.P. Emerson et al., ESO Messenger 117, 27, 2004.

Chapter VIII 1)

Galileo Galilei, Sidereus Nuncius. e.g. R.W. Smith, The Space Telescope, Cambridge U. Press, 1989. 3) Scientific Research with the Space Telescope, IAU Coll. 54, pp. 10-13, 1979. 4) NGST Science and Technology Exposition, Astronomical Society of the Pacific Conf. Proc. 207, 2000. 5) R. de Jong et al., Space Telescope Science Institute Newsletter 20, iss. 1, p. 11, 2003. 6) R. Gilmozzi, P. Dierickx, OWL, ESO Messenger 100, 1, 2000. 7) Extremely Large Telescopes, ESO Conf. Proc. 57, 2000. 8) Astrophysical Journal Letters 538, L1ff, 2000. 9) Ibidem 619, L1ff, 2005. 10) GAIA, ESA BR-163, 2000. 11) Science 308, 935, 2000. 2)

Chapter IX 1) 2)

John Milton, Paradise Lost, Book II, 951-953, 1667. For a general overview of radio astronomical topics, see K. Rohlfs, T.L. Wilson, Tools of Radio Astronomy, 4th ed. 2003, Springer Verlag; B. Burke, F. GrahamSmith, Introduction to Radio Astronomy.

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3)

Various articles in recent publications describe the radio arrays in some detail. See for example IAU Symposium 205, 2001 and Astronomical Society of the Pacific Conference Proceedings 306, 2004. 4) D. Hughes et al., Nature 394, 241, 1998. 5) From a longer list presented by L.-Å. Nyman at the R. Booth 65th birthday symposium, available on the Onsala Space Observatory website. 6) APEX – the Atacama Pathfinder Experiment, L.-Å. Nyman, P. Schilke, R.S. Booth, ESO Messenger 109, 18, 2002. 7) LSA: Large Southern Array, ed. D. Downes, 1995. 8) Science with large millimetre arrays, ed. P. Shaver, ESO Astrophysics Symposia, Springer-Verlag, 1996. 9) The Atacama Large Millimetre Array, R. Kurz, S. Guilloteau, P. Shaver, ESO Messenger 107, 7. 2002. Science with the Atacama Millimeter Array (ALMA), Astronomical Society of the Pacific Conference Proceedings 235, 2001. 10) Y. Sekimoto, Astronomical Society of the Pacific Conference Proceedings 235, 245, 2001. 11) Science with the Square Kilometre Array, ed. C. Carilli, S. Rawlings, New Astronomy Reviews 48, 979-1563, 2004. For a brief more general account see Science, 296, 830, 2002. 12) LOFAR, H. Röttgering et al. in “Texas in Tuscany”, World Scientific, Singapore, 2003. 13) Science 307, 1194, 2005.

Chapter X 1)

H. Curien, Uranie et Cassandre: La coopération européenne dans l’Espace, ESA Journal 2, 93, 1978. The risk of overdependence on the US should, however, not be neglected. One should ensure that the part of our scientific activity that depends on American decisions, taken on the basis of considerations that are not necessarily our own, does not become too preponderant… Dependence. Independence. Interdepence and overdependence. There would be a good subject for a dissertation and that not only in space. 2) A more detailed comparison between the US and European space science budgets for 2004 is as follows. The FY 2004 budget contains five major headings: Solar System exploration, Mars exploration, Astronomical search for origins, Structure and evolution of the universe, and Sun-Earth connection. Under each of these (except Mars) are four subheadings: Development, Operations, Research and Technology, and advanced concepts. Development essentially covers the construction cost of satellites and instruments. The totals for these four are respectively 905, 399, 887 and 1185 MUS$ plus shares of the 595 MUS$ Mars program. The research has only a minor counterpart in the ESA budget, since in Europe research is funded not only through national space agencies, but also through universities, research councils, etc. In the nineties the European space agencies reported national space spending averaging 58% of their contribution to ESA. In the major countries this should be by now an optimistic assumption. So to make a conservative comparison, we group the ESA budget items according to the NASA headings and multiple these by 1.58, while we count only half of the “research” in the NASA budget. Expressing everything in M€ with 1 € = 1.2 US$, we reach the following comparison:

Notes

Solar System (incl. Mars) Sun-Earth connection Astronomical … + universe

NASA (-1/2 “research”) 1460 560 930 2950

297

ESA 107 20 273 400

× 1.58 170 30 430 630

where we have distributed the basic activities in the ESA budget pro rata. Of course, at ESA the distribution over the programs changes from year to year. We note that the total projected spending in 2004 exceeded the ESA contribution level by some 30 M€. So even with optimistic estimates the difference between the US and Europe in the space sciences is a factor of five. 3) European Space Science Horizon 2000, ESA SP-1070, 1984. 4) Horizon 2000 Plus, ESA SP-1180, 1995. 5) US-European Collaboration in Space Science, pp. 68, 67, National Academy Press, Washington, 1998. 6) Horizon 2000 Plus, p. 31. 7) Ibidem, p. 35. 8) Science 300, 719, 2003. 9) Ibidem, p. 881.

Chapter XI 1)

Thomas Hardy, Two on a Tower, Chapter 1, 1882. M.F. Kessler et al., The Infrared Space Observatory (ISO) mission, Astronomy and Astrophysics 315, L27ff, 1996. 3) Several articles in Advances in Space Research (COSPAR) 34, no. 3, 2004. 4) COBE, dark matter and large-scale structure in the Universe, K.M. Górski, A.J. Banday, Chapter 18 of “The Century of Space Science”, ed. J.A.M. Bleeker, J. Geiss, M.C.E. Huber, Kluwer Academic Publishers, 2001. 5) W. Hermsen, COS B, Advances in Space Research 10, 69, 1990. 6) B.G. Taylor et al., The EXOSAT mission, Space Science Reviews 30, 479, 1981. 7) The ROSAT mission, J. Trümper, Advances in Space Research 2, 241, 1982. ROSAT: A New Look at the X-ray Sky, J. Trümper, The Quarterly Journal of the Royal Astronomical Society 33, 165, 1992. 8) The SAX mission for X-ray astronomy, R.C. Butler and L. Scarsi, Observatories in Earth Orbit and Beyond, ed. Y. Kondo, Kluwer Academic Publishers, p. 141, 1990. 9) XMM-Newton observatory, F. Jansen et al., Astronomy and Astrophysics 365, L1ff, 2001. 10) For other X-ray missions see numerous articles in X-ray Astronomy 2000, Astronomical Society of the Pacific Conference Proceedings 234, 2001. 11) XEUS, Proposal to ESA, 2004. 12) SIGMA: the hard X-ray and soft gamma-ray telescope on board the GRANAT space observatory, J. Paul et al., Advances in Space Research 10, 223, 1990. 13) V. Schönfelder, New Astronomy Reviews 48, 193, 2004. 14) The INTEGRAL mission, C. Winkler et al., Astronomy and Astrophysics 411, L1ff, 2003. 15) ESO Messenger 113, 45-48, 2003. 2)

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16)

ESO Messenger 113, 40-44, 2003. AGILE, M. Tavani, American Institute of Physics, Conference Proceedings 587, 729, 2001. 18) The Cerenkov telescopes are desribed in several articles, New Astronomy Reviews 48, 323-366, 2004. 17)

Additional notes to Table XI, 2: 19)

Pub. Astron. Soc. Japan 46, L37, 1994. Astron. Soc. Pacific Conf. Series 234, 4, 2001. 21) Ibidem, p. 611. 22) Ann. Rev. Astron. Astrophys. 30, 391, 1992. 23) Ref. 8, p. 63. 24) Ref. 12, p. 297. 25) New Astronomy Reviews 48, 431, 2004. 26) Ref. 17, p. 722. 20)

The ESA missions are also detailed in the biannual reports of ESA to COSPAR.

Chapter XII 1)

Plato, Timaeus, 22. H.U. Keller, L. Jorda, Chapter 52 of “The Century of Space Science”, ed. J.A.M. Bleeker, J. Geiss, M.C.E. Huber, Kluwer Academic Publishers, 2001. 3) Nature 383, 469, 1996. 4) Rosetta: ESA’s Comet Chaser, C. Berner et al., ESA Bulletin 112, 10, 2002. 5) The Death of a Comet and the Birth of Our Solar System, H. Boenhardt, Science 292, 1307, 2001. 6) High Ambitions for an Outstanding Planetary Mission: Cassini-Huygens, J.-P. Lebreton et al., ESA Bulletin 120, 11, 2004. 7) B. Levrard et al., Recent ice-rich deposits formed at high latitudes on Mars by sublimation of unstable equatorial ice during low obliquity, Nature 431, 1072, 2004. 8) Chapter 57 of “The Century of Space Science”. 9) ESA’s Mars Express Mission – Europe on its Way to Mars, R. Schmidt et al., ESA Bulletin 98, 56, 1999. 10) G. Neukum et al., Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera, Nature 432, 971, 2004. 11) J.B. Murray et al., Nature 434, 352, 2005. 12) Science 307, 1390, 2005. 13) Science 307, 1576ff, 2005. 14) A Solar-Powered Visit to the Moon, G. Racca et al., ESA Bulletin 113, 14, 2003. 2)

Chapter XIII 1)

A general review of solar physics is presented in “Dynamic Sun”, edited by B.N. Dwivedi, Cambridge University Press, 2004. Chapter 20 of that book by B. Fleck and C.U. Keller gives a complete overview of “Solar observing facilities”. In the first chapter of “The Dynamic Sun” edited by A. Hanslmeier et al., Kluwer Academic Publishers, 2001. B. Fleck presents “Highlights from SOHO and future Space

Notes

299

Missions”. An excellent review on “The Solar Atmosphere” by S.K. Solanki and R. Hammer may be found in “The Century of Space Science”, edited by J.A.M. Bleeker, J. Geiss and M.C.E. Huber Kluwer Academic Publishers, 2001, chapter 45. In the same volume several other chapters on the Sun are worth reading.

Chapter XIV 1)

E. Freundlich, Die Grundlagen der Einsteinschen Gravitationstheorie, Verlag Julius Springer, p. 48, 1916. [The experimental foundation of Einstein’s theory of gravitation has not yet come very far. That the theory nevertheless can claim universal respect already today has its full justification in the unusual unity and consequentiality of its basis.] 2) For a general description of cosmic-rays: Astrophysics of Cosmic Rays, by V.S. Berezinskii et al., North Holland Press, Amsterdam 1990; composition around the knee, Astroparticle Physics 14, 245, 2001 and 20, 641, 2004, and for space projects at the highest energies, Astroparticle Physics 20, 391, 2004. Excellent reviews of the whole subject of particle astrophysics and gravitational waves are given in “Cosmic Ray, Particle and Astroparticle Physics”, ed. A. Bonnetti, I. Guidi, B. Monteleoni, Atti dei Convegni Lincei 133, Roma, Ac. Naz. dei Lincei. While these reviews are nearly a decade old, they very well describe the projects that were being started and are only now approaching completion. This has the advantage that there are fewer technical details, while the motivation and physical background are extensively discussed. For recent updates see “Texas in Tuscany”, XXI Symposium on Relativistic Astrophysics, ed. R. Bandiera, R. Maiolino, F. Mannucci, World Scientific, Singapore 2003, and the book “Cosmic Ray Astrophysics” by R. Schlickeiser, Springer-Verlag, 2002.

Chapter XV 1)

Lucretius, De rerum natura, ch. 2, strophe 1056-1077. D. Queloz and M. Mayor, Nature 378, 355, 1995. 3) A. Vidal Madjar et al., An extended upper atmosphere around the extrasolar planet HD 209458b, Nature 422, 143, 2003. 4) M. Mayor et al., Setting new standards with HARPS, ESO Messenger 114, 20, 2003. 5) A. Quirrenbach, The Space Interferometry Mission (SIM) and Terrestrial Planet Finder (TPF), 36th Liège Colloquium, 2001, p. 100. 6) ESO Press Release May 2004. 7) C. Moutou et al., The COROT Mission: Status, Astronomical Society of the Pacific Conf. Series 294, 423, 2003. 8) ESA SP-1276, section 5.6, 2004. 9) J.M. Matthews et al., No stellar p-mode oscillations in space-based photometry of Procyon, Nature 430, 51, 2004. 10) W.J. Borucki et al., The Kepler Mission: Finding the Sizes, Orbits and Frequencies of Earth-size and Larger Extrasolar Planets, Astronomical Society of the Pacific Conf. Series 294, 427, 2003. 11) M. Landgraf et al., Darwin, ESA Bulletin 105, 60, 2001. 2)

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Chapter XVI 1)

The Panchatantra (translated by A.W. Ryder). Publication rates for Eastern Europe and also for Japan are more difficult to evaluate because of the presence of some regional or national journals of good quality. However, their share in the journals of Table XVI, 1 is rapidly increasing. For 2002 the values were Armenia 53, Georgia 12, Russia 1284, Ukraine 379 and Japan 2786 pages, normalized as in Table XVI, 2. 3) Science 304, 808, 2004. 4) D. Adam, Nature 415, 728, 2002 describes various errors in citation studies. See also Nature 435, 1003, 2005. 5) Letter from ISI to Aage Sandqvist, Chairman of the Board of A&A, 8 August 2003. 2)

Chapter XVII 1)

C.V. Raman, A Pictorial Biography, S. Ramaseshan, C. Ramachandra Rao, Indian Academy of Sciences, Bangalore 1988, p. 177. 2) R. May, Science 302, 5-65, 2003. 3) R. Hanbury Brown, Quarterly Journal Royal Astron. Soc. 29, 466, 1988. 4) ESA BR-63, The indirect economic effects of the European Space Agency’s Programmes, April 1991.

Chapter XVIII 1)

Rig Veda, Book X, 129 (translated by R.J.H. Griffith). Creating the International Space Station, D.M. Harland, J.E. Catchpole, SpringerVerlag 2002, p. 97. 3) For a description of the negotiations on the Space Station see R.M. Bonnet, V. Manno, International Cooperation in Space, Harvard University Press, 1994, pp. 108-119. 4) Nature 431, 888, 2004. 5) M. Griffin, testimony to US House Science Committee in 2004, as reported in Science 307, 1709, 2005. 6) For a description of Spacelab see R.M. Bonnet, V. Manno, pp. 78-80. 7) Ibidem, p. 119. 2)

Chapter XIX 1)

Charles de Gaulle, Mémoires d’Espoir, le Renouveau 1958–62, éd. Plon 1970 between Europeans from the Atlantic to the Ural.

Acronyms and Concepts

–A– A AAO AAT ABRIXAS ACE ACP ACS AGASA AGILE AGN ALMA alt-azimuth AMANDA AMBER AMPTE AMS ANTARES ANS antimatter Antu ANU AO Apache Point APEX μ Arae ARC ARCHEOPS Arecibo Ariane Ariel ARISE Asca

Austria Anglo Australian Observatory Anglo Australian Telescope A BRoad band Imaging X-ray All-sky Survey (D, failed) Advanced Composition Explorer (NASA) Aerosol Collector and Pyrolyser (on Huygens) Advanced Camera for Surveys (HST) Akeno Giant Air Shower Array Astro-rivelatore Gamma a Immagine Leggero (I) Active Galactic Nuclei Atacama Large Millimeter Array telescope with one horizontal and one vertical axis Antarctic Muon And Neutrino Detector Array (US) Astronomical Multiple BEam Recombiner (at VLT) Active Magnetospheric Particle Tracer Explorer Alpha Magnetic Spectrometer Astronomy with a Neutrino Telescope and Abyss environmental RESearch Astronomical Netherlands Satellite negatively charged nuclei + positrons unit telescope-1 of the ESO VLT Australian National University Adaptive Optics; also Announcement of Opportunity site in New Mexico Atacama Pathfinder Experiment (ESO) star with planet • 14 earth masses Astrophysical Research Consortium (US) balloon experiment for CMB location 300 m fixed radio telescope European rocket (now Ariane 5) UK satellite series Advanced Radio Interferometry between Space and Earth (US) Japanese hard X-ray satellite

302

ASPERA ASTE ASTRO-E ASTRO-F Astron ASTROSAT AT AU Auger Aurora AVO AXAF

Europe’s quest for the Universe

Analyser of Space Plasmas and EneRgetic Atoms (on Mars Express and Venus Express) Atacama Submillimeter Telescope Experiment (J) Japanese X-ray satellite now named Suzaku Japanese IR satellite Russian γ-ray satellite Indian X-ray and uv satellite Australia (radio) Telescope 1. Astronomical Unit (Sun-Earth distance); 2. Accounting Unit of ESA (N euro) Extreme energy cosmic ray detection system (named after Pierre Auger) 1. Magnetospheric particles hitting earth atmosphere; 2. ESA Mars program Astrophysical Virtual Observatory Advanced X-ray Astrophysics Facility, now NASA’s Chandra –B–

B Beagle-2 BepiColombo BeppoSAX Big Bang BIMA BISON black body BOOMERANG bow shock

Belgium Lander for Mars Express (failed) future ESA mission to Mercury (named after B. Colombo) Italian X-ray satellite (named after Beppo Occhialini) event at origin of the expanding universe Berkeley-Illinois-Maryland Array BIrmingham Solar Oscillations Network ideal radiator producing a spectrum which depends only on the temperature Balloon Observations of Millimetric Extragalactic Radiation ANd Geophysics separates undisturbed medium from that perturbed by object moving supersonically –C–

12

C, 13C Calama Calar Alto CANGAROO

Capodimonte Cargèse Cas A Cassegrain Cassini Castelgrande CAT CCD

isotopes of carbon (6 protons + 6 respectively 7 neutrons) nearest town with airport for ALMA/APEX site of German-Spanish observatory Collaboration of Australia and Nippon for a GAmma-Ray Observatory in the outback observatory in Napoli location of 1983 VLT conference on Corsica remnant of 1680 (?) supernova two mirror telescope mission to Saturn site in Southern Italy Coudé Auxiliary Telescope (at La Silla) Charge Coupled Device

Acronyms and Concepts

CDS

303

1. Coronal Diagnostic Spectrometer (on SOHO); 2. Centre de Données Stellaires (now: Astronomiques) CELESTE CErenkov Low Energy Sampling and Timing Experiment CELIAS Charge ELement and Analysis System (on SOHO) CELT California Extremely Large Telescope ; See TMT Centaurus A nearest radio galaxy cepheid a type of variable star Cerenkov radiation radiation from energetic electrons CERN Centre Européen de Recherche Nucléaire CFHT Canada-France-Hawaii Telescope CGRO Compton Gamma-Ray Observatory (NASA) CH Switzerland CH4 methane Chacaltaya site in Bolivia Chajnantor site in Chile Chandra NASA X-ray facility Churyumov-Gerasomivitch – target comet for Rosetta Circinus galaxy nearby active galaxy citation index normalized count of references Cluster ESA mission of four magnetospheric satellites CMB Cosmic Microwave Background CNES Centre National d’Expériences Spatiales (F) CNRS Centre National de Recherche Scientifique (F) CO carbon monoxyde Co Calan site in Chile Co Chaupiloma site in Chile Co Chico site in Chile Co Duran site near La Silla Co La Montura site near Paranal Co La Peineta site in Chile Co La Silla ESO site in Chile Co Las Campanas site in Chile Co Pachon site in Chile Co Paranal ESO site in Chile Co Peralta site in Chile Co S. Cristobal site in Santiago, Chile Co Tacora volcano in Chile Co Tololo site in Chile Co Vizcachas site near La Silla COBE COsmic Background Explorer (NASA) COME-ON early ESO adaptive optics system COMPTEL COMPton TELescope (D) on NASA’s Compton Observatory Concordia French-Italian base in Antarctica CONICA COudé Near Infrared Camera (at VLT, but now at Nasmyth focus) Constellation planned NASA four spacecraft X-ray mission CONTOUR COmet Nucleus TOUR (NASA, failed) Coonabarabran site in Australia

304

Copiapo cornerstone COROT COS-B cosmic rays Cosmic Vision COSPAR COSTAR COSTEP coudé Crab Nebula CRIRES

Europe’s quest for the Universe

town in Chile large ESA mission COnvection, Rotation and Transits early ESA γ-ray mission energetic particles from beyond earth environment ESA’s current science plan COmmittee on SPAce Research Corrective Optics Space Telescope Axial Replacement (on HST) COmprehensive measurements of the SupraThermal and Energetic Particle populations (on SOHO) fixed focus of telescope remnant supernova 1054 CRyogenic InfraRed Echelle Spectrograph (at VLT) –D–

D dark matter Darwin Deep Impact delay line diffraction limited DIMM DISCO

Germany invisible, gravitating matter ESA proposal for earth-like planet search NASA comet mission compensates variable optical path length in interferometer with the intrinsic angular resolution of perfect optics Differential Image Motion Monitor Dual Irradiance and Solar Constant Observatory (ESA, not selected) DISR Descent Imager / Spectral Radiometer (on Huygens) DIVA Deutsches Interferometer für Vierkanalphotometrie und Astrometrie (cancelled) Dk Denmark DM Deutschmark, past German currency: 1 € = 1.96 DM Dome C site in Antarctica, location of “Concordia” Doppler effect change in wavelength due to motion of emitter Double Star China-ESA two magnetospheric satellites mission Dutch open telescope – solar telescope at La Palma DWE Doppler Wind Experiment (on Huygens) Dwingeloo location of EVN center (NL) –E– EAS EAS-TOP EC échelle grating ECF Eddington Effelsberg EFOSC

1. Extensive Air Shower due to cosmic-ray particle; 2. European Astronomical Society EAS array near Gran Sasso (I) European Commission permits stacking of spectral segments on a square detector European Coordinating Facility for HST (at ESO, Garching) proposed ESA mission for occultations by exoplanets and astroseismology site in Germany ESO Faint Object Spectrograph Camera

Acronyms and Concepts

305

EGRET

Energetic Gamma-Ray Experiment Telescope, on NASA’s Compton observatory Ei Eire or Ireland Einstein NASA X-ray mission EIT Extreme Ultraviolet Imaging Telescope (on SOHO) ELDO European Launcher Development Organization El Leoncito site in Argentina El Niño part of climatological cycle in S. Pacific ELT Extremely Large Telescope e-MERLIN upgrade of MERLIN EPIC European Photon Imaging Camera (on XMM-Newton) Equivalence Principle – states equivalence inertial and gravitational mass ERNE Energetic and Relativistic Nuclei and Electron experiment (on SOHO) ESA European Space Agency ESF European Science Foundation ESO European Southern Observatory ESOC European Space Operations Centre ESP Spain ESRIN ESA establishment in Frascati (I) ESRO European Space Research Organisation ESTEC European Space research and TEchnology Centre EU European Union; here frequently used for earlier 15-country EU + Iceland, Norway, Switzerland EURO 50 proposed 50-m telescope EUSO proposed ESA Extreme Universe Space Observatory EUV Extreme UltraViolet eV electron volt, a unit of energy e-VLA upgrade of VLA EVN European VLBI Network EXIST Energetic X-ray Imaging Survey Telescope (US) exoplanet planet around star other than the Sun EXOSAT European X-ray Observatory SATellite –F– F FAME FIRST FLAMES fleximission Fly’s Eye FOC FORS FOS FOV FREGATE FUSE

France Full-sky Astrometric Mapping Explorer (NASA, cancelled) Far InfraRed Space Telescope, now ESA’s Herschel Fibre Large Array Multi-Element Spectrograph (at VLT) low cost ESA mission Cosmic-ray detector (Utah) Faint Object Camera on HST FOcal Reducer/low dispersion Spectrograph (at VLT) Faint Object Spectrograph (on HST) Field Of View FREnch GAmma-ray TElescope (on NASA’s HETE) Far Ultraviolet Spectroscopic Explorer (NASA)

306

Europe’s quest for the Universe

–G– GAIA Galactic Center Galaxy galaxy GALEX GALLEX Gamsberg GCMS GDP Gemini GENIE GEO-600 GHRS Giacobini-Zinner Ginga Giotto GLAST GMT GMRT GOES-12 GOLF GONG GPO GR GRAAL GRANAT Gran Sasso GRANTECAN GRASP gravitational waves Gravity Probe B GRB Grigg-Skjellerup GTM

Global Astrometric Interferometer for Astrophysics (ESA) the center of our Galaxy at 25000 light years distance our Milky Way galaxy large assembly of stars and gas GALaxy evolution EXplorer (NASA) GALLium EXperiment (neutrinos) site in Namibia Gas Chromatograph Mass Spectrometer (on Huygens) Gross Domestic Product two international 8-m telescopes Ground based European Nulling Interferometer Experiment (at VLT) Gravitational wave detector (D, UK) Goddard High Resolution Spectrograph (on HST) a comet visited by NASA’s ISEE-3 Japanese X-ray satellite ESA spacecraft to comet Halley Gamma-ray Large Area Space Telescope (NASA) Giant Magellan Telescope (US) Giant Metrewave Radio Telescope (India) Geosynchronous Operational Environmental Satellite, No 12 (NASA) Global Oscillations at Low Frequency (on SOHO) Global Oscillation Network Group Grand Prisme Objectif, a small La Silla telescope Greece Gamma-Ray Astronomy at ALmeria Russian γ-ray satellite mountain in central Italy with underground laboratories GRAN TElescopio de las CANarias (ESP) Gamma-Ray Astronomy with Spectroscopy and Positioning (ESA, not selected) waves in the fabric of space-time large NASA satellite to study General Relativity Gamma-Ray Burst second comet visited by Giotto Gran Telescopio Millimetrico (Mexico/US) –H–

H 2H H2 habitable zone Hakucho

hydrogen with a nucleus containing one proton deuterium, with a nucleus containing 1 proton + 1 neutron molecular hydrogen; each molecule contains two H atoms the domain in a planetary system where earth-like planets can retain liquid water on their surface Japanese solar X-ray satellite

Acronyms and Concepts

HALCA Halley’s Comet Hanle HARPS Hartebeestpoort HASI Haverah Park HAWK-I HCN HDF HEGRA Helios 1, 2 HEMT Herschel H. Hertz HESS HET HETE HIFI Hintori Hipparcos H2O Horizon 2000 Horizon 2000-Plus Horizons 2000

307

HRI HRSC H2S HSP HST Huygens Hz

Japanese satellite with radio telescope comet with 76 year period which has appeared since antiquity site in Indian Himalayas High-Accuracy Radial velocity Planetary Searcher (at La Silla) site in South Africa Huygens Atmospheric Structure Instrument (on Huygens) site in the UK new near-IR wide field camera (at VLT) hydrogen cyanide Hubble Deep Field High Energy Gamma-Ray Astronomy (D, at La Palma) German probes of the solar wind High Electron Mobility Transistor future far IR ESA satellite (was FIRST) German radio telescope (in Arizona) High Energy Stereoscopic System (D, in Namibia) Hobby Eberly Telescope (Texas) High Energy Transient Explorer (NASA) Heterodyne Instrument for the Far-IR (on Herschel) Japanese solar X-ray satellite HIgh Precision PARallax COllecting Satellite (ESA) water ESA long term plan follow up to Horizon 2000 Horizon 2000 + Horizon 2000-Plus, now named Cosmic Vision High Resolution X-ray Imager High-Resolution Stereoscopic Camera (on Mars Express) hydrogen sulphide High Speed Photometer (on HST) Hubble Space Telescope ESA sonde to Titan Hertz; unit of frequency equal to one cycle per second

I IAU IBIS IC Ic ICECUBE IFU IHAP ILIAS Impact factor INSU INTEGRAL IR

–I– Italy International Astronomical Union Imager on Board the INTEGRAL Satellite Instrumentation Committee (ESO) Iceland Large neutrino detector in Antarctica Integral Field Unit for spectroscopy Image Handling And Processing system (ESO) Integrated Large Infrastructures for Astroparticle Science based on citation rates of a journal Institut National des Sciences de l’Univers (F) INTErnational Gamma-Ray Astronomy Laboratory InfraRed

308

IRAM IRAS IRTS ISAAC ISAS ISDC ISEE ISO ISOCAM ISOPHOT isoplanatic patch ISS IUE

Europe’s quest for the Universe

Institut de Radio Astronomie Millimétrique Infrared Astronomical Satellite InfraRed Telescope in Space (Japan) Infrared Spectrometer And Array Camera (at VLT) Japanese space science agency INTEGRAL Science Data Centre International Sun Earth Explorers ESA Infrared Space Observatory camera of ISO photometer of ISO angular area over which adaptive optics corrections are constant International Space Station International Ultraviolet Explorer –J–

J Jansky JAXA JCMT JEM-X JENAM JIVE Jodrell Bank JOSO juste retour JWST

Japan unit of electromagnetic flux; 1 Jy = 10-26 watt m-2 Hz-1 Japanese Space Agency James Clark Maxwell Telescope (submm, UK, NL) Joint European X-ray Monitor (on INTEGRAL) Joint European National Astronomy Meeting Joint Institute for VLBI in Europe site in UK Joint Organisation for Solar Observatories where every country gets contracts in proportion to its contributions James Webb Space Telescope (was NGST) –K–

Kamiokande KAMLAND KASCADE Keck 1, 2 Kepler Kepler’s laws Kitt Peak KMOS KORONAS Kourou Kreuz comets Kuyen

Japanese neutrino detector KAMioka Liquid scintillator Anti-Neutrino Detector (Japan) KArlsruhe Shower Core and Array DEtector (D) telescopes on Hawaii (US) European Mars mission (not implemented). NASA exoplanet mission describe properties of planetary orbits site in Arizona new near IR Multi-Object Spectrograph (ESO) solar activity satellite (Russia) European launch site in French Guyana class of comets with perihelia close to the Sun unit telescope-2 of the ESO VLT –L–

L1 L2 La Niña

first Lagrangian point sunwards from earth second Lagrangian point in antisolar direction part of climate cycle in S. Pacific

Acronyms and Concepts

La Palma La Réunion LASCO LBT LDEF LEP LEST LHC LGS Lick LIGO LINEAR LISA LMC LMT Lobster-ISS LOFAR Long March LSA LWS

309

island of the Canary Islands island in S. Indian Ocean Large Angle and Spectroscopic COronograph (on SOHO) Large Binocular Telescope Long Duration Exposure Facility (NASA) Large Electron Positron collider at CERN Large European (later Earth based) Solar Telescope (abandoned) Large Hadron Collider at CERN Laser Guide Star observatory in California Laser Interferometer Gravitational wave Observatory (US) a comet that disintegrated Laser Interferometer Space Antenna Large Magellanic Cloud Large Millimeter Telescope (Mexico, US) proposed hard X-ray survey instrument on the Space Station (ESA) LOw Frequency ARray (NL) Chinese launcher Large Southern Array (now ALMA) Long Wavelength Spectrometer (on ISO) –M–

MACAO M1, 2, 3 MACRO MAG Magellan 1, 2 MAGIC magnetopause magnetosphere magnitude Maidenak MAMBO MARS Mars-96 Mars Express Mars Observer MARSIS Mauna Kea McDonald MDI Medicina

Multi Application Curvature Adaptive Optics (at VLT) the first three reflecting mirrors in a telescope particle detector under the Gran Sasso (I) MAGnetometer (on Venus Express) 6.5-m telescopes (US) Major Atmospheric Gamma-ray Imaging Cerenkov telescope (D) the surface separating the solar wind from the region dominated by the magnetic field of the earth the region controlled by the earth’s magnetic field logarithmic unit of brightness ; + 5 mag corresponds to a factor of 100 fainter site in Uzbekistan MAx-Planck Millimeter BOlometer MArs Radio Science experiment (on Mars Express) Russian Mars mission (failed) ESA Mars mission NASA Mars mission (failed) Mars Advanced Radar for Subsurface and Ionospheric Sounding (on Mars Express) mountain in Hawaii observatory in Texas Michelson-Doppler Interferometer (SOHO) site near Bologna

310

Melipal MERLIN Messenger MESUR Metsähovi MICROSCOPE MIDAS MIDI Mileura Mills spectrograph MIRI μm MMA MMT MPE MPG MPIA MPIfR MSX Mt Graham Mt Hopkins Mt Palomar Mt Wilson

Europe’s quest for the Universe

unit telescope-3 of the ESO VLT Multi-Element Radio-Linked INterferometer (UK) ESO journal Mars Environmental SURvey (NASA, not selected) site in Finland MICROSatellite à trainée Compensée pour l’Observation du Principe d’Equivalence Munich Interactive Data Analysis System (ESO) MID-Infrared interferometric instrument (at VLT) site in W. Australia early instrument in Chile (US) Mid-InfraRed Instrument (for JWST) micrometer (0.001 mm) MilliMeter Array (US) Multi-Mirror Telescope (Arizona) Max-Planck-Institut für Extraterrestrische Physik (Garching) Max-Planck-Gesellschaft Max-Planck-Institut für Astronomie (Heidelberg) Max-Planck-Institut für Radioastronomie (Bonn) Midcourse Space Experiment (US) site in Arizona site in Arizona site in California site in California –N–

N NACO Nancy Nanshan NAOS NASA Nasmyth telescope NESTOR neutrino NGST NH3 NICMOS

Norway NAOS-CONICA (at VLT) site in France site in China Nasmyth Adaptive Optics System (at VLT) National Aeronautics and Space Administration (US) three mirror telescope European neutrino detector nearly weightless particle with weak interaction with matter Next Generation Space Telescope (now JWST) ammonia Near Infrared Camera and Multi-Object Spectrograph (on HST) NIRCam Near InfraRed Camera (for JWST) NIRSpec Near InfraRed Spectrograph (for JWST) NL Netherlands Nobeyama site in Japan Noto site in Sicily NTT New Technology Telescope (ESO) NTT hill hill adjacent to Paranal nulling interferometer – interferometer with destructive interference eliminating the central image

Acronyms and Concepts

311

–O– O2 O3 Odin OECD OH Olympus Mons OM OMC OMEGA Omega CAM ONERA Onsala Oort Cloud OPTICON Oukamaiden OWL

molecular oxygen ozone Swedish satellite for radio astronomy and aeronomy Organisation for Economic Co-operation and Development molecule with prominent radio lines volcano on Mars Optical Monitor (on XMM-Newton) Optical Monitor Camera (on INTEGRAL) Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (on Mars Express) large area camera for VLT Survey Telescope Office National d’Etudes et de Recherches Aéronautiques et Spatiales (F) site in Sweden cloud of comets enveloping the solar system OPTical Infrared COordination Network site in Morocco OverWhelmingly Large telescope (ESO) –P–

P PACS PAH Pampa S. Eulogio Panamericana Parkes 51 Pegasi Pelícano PFS PI Pico Veleta PL Planck Plateau de Bure postdoc PPARC PRIMA prime focus pulsar

Portugal Photoconducting Array Camera and Spectrometer (on Herschel) Polycyclic Aromatic Hydrocarbon site in Chile road from Alaska to Chile site in Australia star with the first exoplanet detection river at the foot of La Silla Planetary Fourier Spectrometer (on Mars Express and Venus Express) Principal Investigator site in Andalusia Poland ESA mission to study the cosmic microwave background site in the French Alps person holding a, usually not permanent, postdoctoral appointment Particle Physics and Astronomy Research Council (UK) Phase Referenced Imaging and Microarcsecond Astrometry (at VLT) telescope focus reached after one reflection a rotating magnetic neutron star emitting pulses of radiation –Q–

quasar QPO

an Active Galactic Nucleus with much stronger emission than the surrounding galaxy Quasi Periodic Oscillation (e.g. in X-ray binaries)

312

Europe’s quest for the Universe

–R– R&D REM resolution

Research and Development Rapid Eye Mount (La Silla) the smallest separation observable in angular (Δθ) or wavelength (Δλ) measure. Spectroscopic resolution is frequently expressed as λ/Δλ. RGS Reflection Grating Spectrometer (on XMM-Newton) RHESSI Ramaty High Energy Solar Spectroscopic Imager (NASA) Rio Frio site in Chile Röntgen Kvant Russian X-ray instrument on MIR space station Roque de Los Muchachos – site on La Palma in the Canary Islands ROSAT Röntgen Satellite (D) Rosetta ESA’s comet mission ROSITA RÖntgen Survey with Imaging Telescope Array (D, ESA) RTG Radio isotope Thermoelectric Generator RXTE Rossi X-ray Timing Explorer (NASA) –S– S Sweden SAFIR Single Aperture Far InfraRed telescope (NASA proposal) Sag A* radio center of our Galaxy SAGE Soviet-American Gallium Experiment SALT Southern African Large Telescope San Pedro de Atacama – village in Chile San Pedro Mártir site in Mexico SAO Smithsonian Astrophysical Observatory (US) SAS-2 Small Astronomical Satellite (γ-rays, NASA) SAX Satellite italiano per l’Astronomia a raggi X (now BeppoSAX) SCUBA Submm Common User Bolometer Array (on UKIRT) SDO Solar Dynamics Observatory (NASA) Seshan site in China SEST Swedish-ESO Submm Telescope (no longer operating) Seyfert galaxy a lower luminosity quasar SF Finland Si IX spectral line from 8 times ionized silicon Siding Springs site in Australia Sierra Negra site in Mexico SIGMA Système d’Imagerie Gamma à Masque Aléatoire SIM Space Interferometry Mission (NASA) SINFONI SINgle Faint Object Near-infrared Investigation (at VLT) SIRTF Space InfraRed Telescope Facility (now Spitzer, NASA) SKA Square Kilometer Array SMA SubMillimeter Array (Mauna Kea) SMART-1 Small Mission for Advanced Research in Technology-1 (ESA) SMC Small Magellanic Cloud SMM Solar Maximum Mission (NASA)

Acronyms and Concepts

313

SN SNO SOAR SOC SOFIA SOHO Solar-B Solar Orbiter Solar Probe solar wind Soyuz spectrograph Spectrum uv SPI SPICA

supernova Sudbury Neutrino Observatory (Canada) SOuthern Astrophysical Research (telescope) Scientific Operations Center Stratospheric Observatory For Infrared Astronomy SOlar and Heliospheric Observatory Japanese X-ray mission future solar satellite (ESA) proposed in situ probe of the solar corona outflow of gas from the solar corona Russian rocket instrument for analyzing light as a function of wavelength Russian mission for ultraviolet observations SPectrometer of INTEGRAL SPace Infrared telescope for Cosmology and Astrophysics (Japan, proposed) SPICAM/V SPectroscopic Investigation of the Characteristics of the Atmosphere of Mars (on Mars Express and Venus Express) SPIRE Spectral and Photometric Imaging REceiver (on Herschel) Spitzer NASA IR mission (was SIRTF) SS Space Station SSP Surface Science Package (on Huygens) STACEE Solar Tower Atmospheric Cherenkov Effect Experiment (US) Star Dust comet tail sample return mission (NASA) STEREO Solar TErrestrial RElations Observatory (NASA) St Katherine site on Sinai peninsula ST-ECF Space Telescope European Coordinating Facility (Garching) STIS Space Telescope Imaging Spectrograph STScI Space Telescope Science Institute (Baltimore) STSP Solar-Terrestrial Science Programme (ESA) Subaru Japanese telescope in Hawaii SUMER Solar Ultraviolet Measurement of Emitted Radiation (on SOHO) Suzaku New name for ASTRO-E SWAN Solar Wind ANisotropies (on SOHO) SWAS Submillimeter Wave Astronomy Satellite (NASA) Swedish Solar Telescope – located at La Palma SWIFT fast response satellite for observing γ-ray bursts (NASA) SWS Short Wavelength Spectrometer (on ISO) synchrotron radiation – radiation from relativistic electrons in a magnetic field –T– TAMA 300 TAROT TD-1 Teíde Teneriffe Tenma

Japanese gravitational wave detector Télescope à Action Rapide pour les Objets Transitoires (La Silla) early ESRO satellite volcano on Teneriffe island among the Canary Islands Japanese X-ray satellite

314

THEMIS 44Ti

Titan TMT TNG Torun TPF TRACE Tunguska

Europe’s quest for the Universe

Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Stellaires (F, I) radioactive titanium isotope satellite of Saturn Thirty Meter Telescope (US) Telescopio Nazionale Galileo (I) on La Palma town in Poland Terrestrial Planet Finder (NASA project) Transition Region And Coronal Explorer (NASA) location of meteoritic impact crater in Siberia –U–

UDF UK UKIRT Ulysses US UT uv UVCS UVES

Ultra Deep Field (taken with HST) United Kingdom United Kingdom InfraRed Telescope (Mauna Kea) mission to study the solar wind in situ United States of America Unit Telescope (of the ESO VLT) ultraviolet UltraViolet Coronal Spectrometer (on SOHO) Uv-Visual Echelle Spectrograph (at VLT) –V–

Vallenar Vega Venus Express VERA VERITAS VIMOS VIRGO Virgo Cluster VIRTIS VISIR VISTA VLA VLBA VLBI VLT VLTI VMC VO Volcano Ranch VSOP VST

town in Chile Russian spacecraft, flew by Giotto ESA’s Venus mission VEnus RAdio occultation instrument (on Venus Express) Very Energetic Radiation Imaging Telescope Array System (US) Visible Multi-Object Spectrograph (at VLT) 1. Variability of IRradiance and Gravity Oscillations (on SOHO); 2. French-Italian gravitational wave detector (near Pisa) aggregate of numerous galaxies some 50 million light years away Visible and InfraRed Thermal Imaging Spectrometer (on Venus Express) VLT Imager and Spectrometer for the mid-InfraRed Visible and Infrared Survey Telescope (at Paranal) Very Large Array (New Mexico) Very Long Baseline Array (US) Very Long Baseline Interferometry Very Large Telescope (ESO) Very Large Telescope Interferometer (ESO) Venus Monitoring Camera (on Venus Express) Virtual Observatory site in New Mexico VLBI Space Observatory Program (Japan) VLT Survey Telescope

Acronyms and Concepts

–W– Wetzel WFPC WIMP WIND Wirtanen WMAP Wolf-Rayet

site in Germany Wide Field and Planetary Camera (on HST) Weakly Interacting Massive Particle spacecraft to study the solar wind (NASA) comet previously targeted by Rosetta Wilkinson Microwave Anisotropy Probe (NASA) type of massive, evolved binary star –X–

XEUS XMM-Newton X-shooter

X-ray Evolving Universe Spectroscopy mission (ESA) X-ray Multimirror Mission (ESA) new wide wavelength range spectrograph (at VLT) –Y–

Yakutsk Yebes Yepun Yohkoh

site in Siberia site in Spain unit telescope-4 of the ESO VLT Japanese solar X-ray satellite –Z–

Zelentchuck Zerodur

site in the Caucasus low expansion material for mirror blanks

315

Index

A AAT, 40 Abbot C.G., 91 active optics, 53, 54 ACS, 129 Acuerdo, 77, 79, 93 Adaptive Optics, 109, 110, 112 Advanced Camera for Surveys, 126 – Composition Explorer, 227, 235 AGASA array, 232 AGILE, 200 Allègre C., 169 ALMA, 49, 96, 99, 100, 106, 149, 151154-158, 182, 183, 186, 280, 281 alt-azimuth, 56 aluminium mirror, 62, 63 AMANDA, 236 AMBER, 120 AMOS, 75, 80 AMPTE, 221 AMS, 236 Andersen Johannes, 31 angular resolution, 22 ANS, 17 Ansaldo/EIE/SOIMI, 71 ANS satellite, 176 Antarctic, 110 Antarctica, 105, 106, 224 ANTARES, 236 AO, 128-130, 135, 229 APEX, 152, 153, 155, 156 ARCHEOPS, 184 architects Fehling and Gogel, 39 Ardeberg Arne, 95 Ariane 5, 162, 182, 184, 221 Ariel, 17, 188, 234

Armazoni, 97, 106 array telescope, 45 ASCA, 194 Astronomical Journals, 254 – researchers, 269 – sites, 105 Atacama, 90, 96, 102, 107, 154 ASTE, 156 ASTRO-E, 194 – E2, 284 – -F, 186, 187, 284 Astrometry, 137 ASTROSAT, 137, 194 astrosital, 56 Auer & Weber, 77 Aurora, 169, 214, 278, 280, 282, 283 Australia Telescope, 145 B Baade Walter, 25 Bachmann Gerhard, 97 background, 128 Bannier J.H., 30 Barrientos S., 107 Beagle-2, 212, 213 Behr Alfred, 29 Bepi Colombo, 164, 215, 216 Beppo, 174 – SAX, 18, 189, 190, 192, 196, 282 beryllium, 66, 74, 82 Big Bang, 183 BISON, 224 Blaauw Adriaan, 30 black hole(s), 115, 116, 121, 241, 279, 280 Bleeker Johan, 163 Blue Book, 67, 70, 73, 80-82

Europe’s quest for the Universe

318

Boller & Chivens spectrograph, 31, 32 Bonnet Roger, 163 BOOMERANG, 184 Booth Roy, 150 bowshock, 220 Breysacher Jacques, 31 C 21-cm line, 140, 141 Calar Alto, 26, 40, 41, 90 Caméra Électronique, 32 CANGAROO III, 202 Cargèse, 60 Cassegrain, 27, 50, 51, 66, 67, 72, 74, 81, 112 Cassini, 167, 208 CAT, 30, 32, 33, 47 CCD, 21, 22, 41, 44, 54, 58, 122 CCDs, 32 CELESTE, 201 Centaurus A, 140, 150 Centre de Données Astronomiques, 253 Cerenkov radiation, 200 CERN, 14, 25, 27, 38, 171, 172 CFHT, 26, 41 Chacaltaya, 95, 105 Chajnantor, 96, 99, 100, 104-106, 110, 152, 154, 155 Chandra, 192, 194 Chile, 26, 37, 77, 78, 79, 82, 90-93, 96, 156 CINI Foundation, 67 Climatic variability, 99 Cluster, 164, 220, 222, 284 CMB, 183, 184 CNES, 168, 169, 206, 246 CO, 141, 151, 157 COBE, 184, 187 COME-ON, 111 comet Churyumov-Gerasimenko, 206, 207 comet Halley, 204, 205 – LINEAR, 207, 208 – Schwassmann-Wachmann 3, 207 – Wirtanen, 206, 207 COMPTEL, 197 Concordia, 106

CONICA, 111 CONSTELLATION–X, 196, 282 Copiapo, 91, 95 Cornell, 104, 106 Corning, 61, 69 corona, 221 Coronal Mass Ejections, 219 COROT, 165, 170, 246 COS B, 161, 188, 197 cosmic-rays, 139, 231-236 Cosmic Vision, 165, 171 COSTAR, 125 coudé, 27, 29 Crab Nebula, 201 Croce del Nord, 143 Curien H., 161 Curtis H.D., 91 D 1.5-m Danish telescope, 37 Dark Energy, 279 – matter, 140, 238, 279 Darwin, 121, 165, 167, 249, 250, 278, 280, 283 Deep Impact, 208 de Gaulle Charles, 289 Denisse Jean-François, 31 de Jonge Peter, 36, 150 delay lines, 119, 121 detectability of planets, 247 DIMM, 103, 104 DISCO, 224 Disney M., 45 DIVA, 137 Dome C, 106 Doppler effect, 244 Dornier, 73 Double Star, 165, 170, 220, 222, 284 E Earliest Universe, 279 earthquakes, 107 EAS, 286 ECF, 287 Eddington, 170, 246 Eduardo Frei Ruiz-Tagle, 79

Index

Effelsberg, 142 EFOSC, 32 Einstein, 188, 194, 231, 238 ELDO, 161, 162 ELTs, 134, 136 Enard Daniel, 31 Equator-S, 221 ESA(’s), 16, 17, 21, 113, 119, 121, 123, 125, 126, 131, 132, 138, 146, 159-235, 240, 241, 245, 246, 265, 266, 270-272, 274, 275, 282, 283, 285-287 – Convention, 163 ESF, 286 ESO, 16-18, 21, 24-120, 125, 127, 134, 145, 150, 152, 154, 161, 171, 172, 266, 270-272, 275, 281, 285-287 – Convention, 17, 26, 49, 77 ESOC, 162 ESRIN, 162 ESRO, 17, 161, 162 ESTEC, 162 European Research Area, 263, 271 EUSO, 170, 234, 285 EVN, 142, 145-147, 282 EXIST, 196 Exoplanets, 170 EXOSAT, 18, 174, 179, 189, 194, 282 Extensive Air Shower, 232 Extreme Energy Cosmic-rays, 279 F FAME, 137 FIRST, 181, 188 FLAMES, 117, 118 FOC, 123, 124 focal ratio, 51 Fogo, 90 Frequency Agile Solar radio Telescope, 230 Freundlich, Erwin, 231 Funding, 270, 271, 275 FUSE, 137 G GAIA, 138, 165, 167, 170, 245, 280 Galactic Center, 115, 116

319

Galaxy Evolution Explorer, 137 Galileo, 67, 167 228 GALLEX, 237 gamma-ray, 188, 190, 196 – – bursts, 190, 198 Gamsberg, 26, 40, 90 Garching, 59 GDP, 258, 260, 265, 268, 270, 271 Gemini, 26, 83-85 – Project, 71 General Relativity Theory, 231, 238 Genesis, 227 GENIE, 121 GEO 600, 239 GIAT, 72 Giacconi Riccardo, 77 Ginga, 194 Ginzburg Vitali, 231 Giordano Bruno, 243 Giotto, 163, 204, 205 GLAST, 169, 200 GOES-12, 227 Golay Marcel, 48 GONG, 224 GRAAL, 201 Graham (Mt.), 83, 84, 90, 104, 105, 150 GRANAT, 196 GRANTECAN, 83-85, 281 Gravitational wave(s), 231, 238, 240, 242 Gravity Probe B, 242 GREGOR, 229 Grigg-Skjellerup, 205 H habitable zone, 247 Hakucho, 188 HALCA, 142, 146, 147 Hale G.E., 13, 16 HARPS, 245 HAWK-1, 117 Heckmann O., 38, 93 HEGRA, 201 Helios, 220 Herschel-Planck, 162, 164, 177, 181-184, 186, 187, 280 HESS, 201, 202, 238, 279 Hess Victor, 231

Europe’s quest for the Universe

320

HET, 83, 85 Hinotori, 227 Hipparcos, 18, 137, 138, 163, 174 H2O, 104, 105, 152 Hofstadt Daniel, 31, 77, 94 Horizon 2000, 163, 165, 167, 171, 205, 214 – -Plus, 164, 170 HST, 55, 110, 123-130, 134, 137, 163, 206, 248, 284 – instruments, 124 Hubble Deep Field, 129 – Ultra Deep Field, 129, 131 Humboldt, 90 Huygens, 208, 209, 216, 284

ISAAC, 114, 115 ISAS, 165 IUE, 17, 161, 162 J Jansky Karl., 14, 139 JAXA, 215 JCMT, 90, 150 JENAM, 286 JIVE, 145 Jodrell Bank, 142 juste retour, 171 JWST, 106, 132-134, 136, 137, 165, 170, 186, 187, 280 – instruments, 124

I IAU, 19, 269, 270, 272, 285 ICECUBE, 236 ILIAS, 287 impact factor(s), 263, 264 inflatable dome, 73 inflation, 81 infrared, 33, 47, 74 – space missions, 187 Instrument(s), 209 – at the VLT, 115 – of ISO, 178 INSU, 80, 148 INTEGRAL, 18, 162, 197-199, 284 Integral Science data Centre, 199 – Field Unit, 117 Interferometers, 143 Interferometrically, 82 interferometry, 65, 67, 73, 80, 81, 107, 119, 120 IR, 104, 106, 107, 110, 111, 114-119, 128130, 136, 176, 179, 181, 185, 249 IRAM, 148, 149, 153, 280, 282 IRAS, 176, 186 Iris, 224 IRTS, 185, 187 ISEE-2, 221 ISO, 18, 132, 162, 163, 176-181, 185-188, 280 ISOCAM, 178, 185 ISOPHOT, 178-180

K KamLAND, 237 KASCADE, 235 Keck telescope(s), 82, 83, 90, 104, 281 Kepler, 247 KMOS, 118 KORONAS-1, 228 Kourou, 162 Kuiper G.P., 91 Krupp-MAN, 56 L L2, 126, 181, 194 Labeyrie A., 45 La Palma, 26, 40, 41, 83, 84, 89, 105, 106, 136, 201, 229 La Peineta, 91 La Réunion, 104, 105 Large Magellanic Cloud, 192, 237 Las Campanas, 50, 83, 93, 94 La Silla, 27, 33-36, 40, 57, 58, 64, 73, 79, 91, 93-95, 98, 100-102, 105-107, 122, 150-152, 199, 245 La Torre, 78 LBT, 83, 84, 85, 281 Léna Pierre, 60, 111 LEST, 229 LHC, 279 LIGO, 239, 241

Index

Linde, 75 LISA, 164, 165, 170, 240-242, 280, 283 – pathfinder, 240 Lobster, 170 – -ISS, 196, 285 Lockman hole, 189, 193 LOFAR, 158, 282 Long Duration Exposure Facility, 234 LSA, 153 Lucretius, 243 Lüst Reimar, 39 M 16-m equivalent telescope, 46 16-m telescope, 79 3.6-m, 27-31, 33, 37, 40, 47, 52 3.6-m telescope, 80, 111 8-m class telescopes, 83 8-m mirror, 69, 71, 73 8.2-m mirror(s), 72, 81 8-m telescopes, 73, 74 MACAO, 111 MACRO detector, 235 Magellan, 83 MAGIC, 89, 201, 202, 279 Magnetic fields, 139, 158 magnetopause, 220 Magnetosphere, 220 Mars, 167-169, 211, 247, 272 – -96, 169, 212, 284 – express, 165, 170, 171, 209, 210, 212214, 216, 284 Mauna Kea, 16, 40, 41, 83, 90, 104-106, 110 MAXIMA, 184 Mayor Michel, 244 Mercury, 164, 168, 215, 216, 284 MERLIN, 144-146 Messenger, 216 MICROSCOPE, 165, 170, 242 Middelburg Frank, 38 Middle European countries, 272 MIDI, 113, 119 MIRI, 133 MMA, 154 MMT, 52, 83 Moon, 169

321

MOST, 247 MPG, 39, 40, 80, 148 MPIA, 40 MPIfR, 152, 153, 156 Muller A.B., 91, 97 multi-mirror telescope, 44, 45 Multiple Object Spectrographs (MOS), 117 N Nancay, (F) radioheliograph, 230 NAOS, 111 NAOS-CONICA, 115, 116 NASA, 18, 119, 125, 130-132, 137, 163165, 167, 168, 170, 171, 176, 184, 185, 192, 194, 196, 199, 200, 205, 206, 208, 213, 216, 223, 226, 227, 234, 240-242, 245, 250, 283, 285, 286 – Astrophysical Data System, 253 Nasmyth, 27, 29, 50, 66, 67, 72, 74, 81, 112 NESTOR, 236 Neutrinos, 231, 236, 237 Newton Isaac, 87, 88 NEXT, 196 NGST, 130, 132 NICMOS, 126 Nicollier Claude, 96 NIRCam, 133 NIRSpec, 133 Normalized pages, 258 NOT, 41 NTT, 35, 41, 49, 50, 52, 55-58, 59, 64, 69, 73, 77, 106, 117, 136 – hill, 58, 98, 114, 122 nulling interferometers, 249 O Observatoire de Haute-Provence, 244 Observatorio del Teide, 229 Odin, 185, 187 OECD, 285, 286 Olympus Mons, 210, 213 OMEGA, 213 ONERA, 111 Onsala, 156

Europe’s quest for the Universe

322

Onsala Space Observatory, 154 Oort, Jan, 25 operation costs, 35 OPTICON, 287 oscillation modes, 223 OWL, 19, 107, 129, 130, 132, 134-137, 248, 278-282 Ozone, 250 P Pacini Franco, 48 Palomar, 13, 16, 28 Panamericana, 97 Paranal, 37, 73, 75, 79, 82, 83, 95-105, 107, 119, 122, 127 Pauli Wolfgang, 231 Pedro Martír, 104, 105 Photometric nights, 103, 105 PI countries on ESA missions, 173 Pierre Auger Observatory, 232 Planck, 165, 170, 182, 184, 187 planetary missions, 209 Pontecorvo Bruno, 237 post docs, 268 PRIMA, 121 prime focus, 27 Q Queloz Didier, 244 R RADIOASTRON, 147 RadioNet, 287 Ramaty High Energy Solar Spectroscopic Imager, 227 REOSC, 63, 70, 71, 73, 84 Residencia, 75-77 RME, 199 Roddier François, 60 ROSAT, 18, 174, 189, 190, 194, 260, 282 Rosetta, 162, 164, 167, 206-208, 214 ROSITA, 196, 285 RTGs, 167 Rutland F. 91 RXTE, 194

S SAFIR, 187 Sag. A*, 117 SAGE, 237 Sagittarius A*, 115 SALT, 83, 85 Sanchez Francisco, 89 San Pedro de Atacama, 94, 99, 152 Sarazin Marc, 95, 99, 101, 103, 104 Schenkirz D., 77 Schmidt telescopes, 122 Schott, 56, 61, 63, 69, 70 Schuster Hans-Emil, 97 SCUBA, 150 segmented mirror, 45 SEST, 150-152 Setti Giancarlo, 48 Sierra negra, 104, 105 SIGMA, 196, 284 SIM, 245 SINFONI, 117 SIRTF, 177, 185, 186 SKA, 157-159, 278, 280-282, 285, 286 SMART-1, 170, 171, 196, 215 Smyth Piazzi, 87 SOFIA, 185 SOHO, 18, 164, 223, 225, 226, 229, 284 – instruments, 224 Solar B, 227 – irradiance, 223 – Maximum Mission, 227 – missions, 228 – Orbiter, 165, 170, 223, 227 – Probe, 227 – wind, 219, 221, 223 South Africa, 91 Soyuz, 162, 170, 215, 222 Spacelab, 285 Space Station, 167, 169, 170, 194, 283, 284, 285 Spectrum uv, 137 SPICA, 186, 187, 284 Spitzer, 185, 187 STACEE, 201 Stardust, 207 steel mirror, 62 ST/ECF, 125 Stephenson R., 88

Index

STEREO, 227 STIS, 126 Stock J., 91, 93, 95 Strewinski W., 27 Strömgren Bengt, 31 STScI, 123, 125 Subaru, 83 submm, 106 – telescopes, 147 Sudbury Neutrino Observatory, 237 Sun grazing comets, 225 SWAS, 187 SWIFT, 199 Swings Jean-Pierre, 59 synthesis methods, 143 T 3.6-m telescope, 63, 64, 245 6-m telescope, 29, 44 8-m unit telescope, 66 TAMA, 239 Tarenghi Massimo, 56, 77 TAROT, 199 TD-1, 161 Teíde Observatory, 88 Teneriffe, 87, 88 Terrestrial Planet Finder, 250, 283 The 3.5–6 meter Astronomical Telescopes, 42 THEMIS, 88, 229 Titan, 208 Tololo, 91, 95, 107 Transition Région And Coronal Explorer, 227 U UKIRT, 40, 90 Ulysses, 18, 163, 223, 235 Universidad católica, 79 – de Chile, 79 US export regulations, 284 USSR, 93, 94 UVES, 113, 117, 118 V Vattani U., 48, 49 Venus, 167, 247

323

Venus express, 165, 170, 214, 216 VERITAS, 201, 202 VIMOS, 117, 118 VIRGO, 239, 240, 241, 280 Virtual Observatory, 122 VISTA, 98, 114, 122, 281 Vizcachas, 94 VLA, 144, 156, 157 VLBA, 145 VLBI, 142, 145-147, 151, 157, 280 VLT, 10, 12, 14, 17, 18, 26, 49, 50, 52, 55, 56-65, 67, 71-73, 77, 80, 83, 85, 94, 97, 99, 100, 103, 109, 111-114, 117119, 128-130, 136, 139, 154, 171, 184, 206, 208, 246, 265, 271, 280, 281 – Advisory Committee, 61 – Study Group, 59 – Survey Telescope, 75, 114 VLTI, 111, 112, 114, 119, 121, 280 VST, 122, 281 W Waldmeier M., 48, 49 Walters K., 93 Westerbork, 144 Wilson Ray, 53, 56 WIND, 221 Whipple temlescope, 201 WMAP, 184, 187 X XEUS, 170, 194, 196, 200, 278, 280, 282, 284 XMM-Newton, 117, 162, 164, 174, 184, 190-192, 194, 199, 282 X-ray, 188 X-shooter, 118 Y 50 year cycle, 101 Yohkoh, 227 Z Zeiss, 41, 57, 63 Zerodur, 56, 57, 61-63, 66, 69, 70, 83 Ziebell Manfred, 73

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ESO ESO Jodrell Bank Observatory, University of Manchester ESO and C. Madsen ESO ESO ESO ESO ESO/Schott ESO/REOSC ESO Instituto de Astrofísica de Canarias Instituto de Astrofísica de Canarias ESO/ESA U. Demierre ESO/University of Munich ESO ESO NASA, ESA and S. Beckwith (STScI) and the HUDF Team NASA/Northrop Grumman Space Technology ESO ESO Max-Planck-Institut für Radioastronomie Istituto de Radioastronomia CNR, Bologna National Radio Astronomical Observatory, US JIVE IRAM ESO ESO/National Observatory of Japan ESA ESA ESA and the ISOCAM Consortium A. Moorwood ESA ESA ESA/G. Hasinger et al. ESA ESA/ISDC ESA/Max-Planck-Institut für Aeronomie/U. Keller ESA ESO ESA/DLR/FU Berlin (G. Neukum) ESA ESA D. Enard/VIRGO Consortium ESA ESO/M. Mayor et al. ESA

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