One approach to learning about stellar populations is to study them at three different levels of resolution. First in our own galaxy; secondly from nearby galaxies where stars can still be resolved; and thirdly in remote galaxies in which the stellar population can only be studied in integrated light. This International Astronomical Union Symposium covered the range of galaxies in its study of their stellar populations. Interspersed with theoretical papers, the observational papers provide a presentation of the progress that has been made in the field.

This book is a synopsis of modern deep-field astronomy, based on the powerful telescopes and instruments developed in recent years. It is organized along topical themes, such as the extragalactic background radiation at different wavelengths, the evolution of galaxies, the history of star formation, the nature of absorbers, the reionization of the intergalactic medium, the validity of photometric redshifts, gravitational lensing, and clustering of galaxies. Stellar and substellar objects were not neglected, however, and one session was devoted to nearby bodies such as trans-Neptunian solar system objects, brown dwarfs, and stars with special characteristics.

As it was said by one of the participants to this workshop" In our attempts to understand the spectral evolution of galaxies, we are fortunate indeed to have the ability to look back in time and observe galaxies as they were billions of years ago. Perhaos in no other discipline is it possible to gain such a direct view to hJstory. The galaxies we seek to study are remote, their light faint, and thus only recently has it become technicaJlv feasible to sample the spectra of normal luminosity galaxies at lookback times of five billion years or more" .... or, perhaps. even to see galaxies in the process of their formation. or shortly afterwards. This fourth workshop organized by the "Advanced School ot Astronomy was indeed centered on the "Spectral Evolution of Galaxies." on reviewing and discussing the relevant astrophysical processes and on assessing our current ability to model and understand the evolution of stellar populations. Following an opening session dealing with some outstanding questions of galaxy evolution. Session I addressed the specific problems of galaxy and star formation processes. topics of uncertainty and controversy to which IRAS observations may give novel perspectives. The properties of stellar populations in the local group of galaxies formed the basis of Session II. Session III dealt with the fundaments of the theory of spectral and photometrical evolution of stellar populations. and with recent developments in the theory of stellar structure. a necessary step to model and understand galactic evolution.

In recent years, it has become clear that the red-giant phase is one of the most dramatic periods in a star's life, when all of its parts become involved in ways that have both direct and indirect observational consequences. This is most particularly true of low- and intermediate mass stars during the second ascent of the giant branch. Such stars bring to their surfaces products of nucleosynthesis currently taking place in their deep interiors, they pulsate as Mira variables, develop extended outward-flowing atmospheres that may exhibit maser properties, and shed great quantities of matter, sometimes highly processed, into the inter stellar medium. The manner in which processed matter is brought to the surface is far from being completely explained, and the precise mechanism or mechanisms whereby matter is ejected from the stellar surface (whether by deposition of Alfven waves, radiation pressure on grains, or as a consequence of so me large scale envelope instability) has yet to be elucidated to every one's satisfaction. The purpose of the second workshop in Astrophysics, organized by the "Advanced School of Astronomy," was to bring together experts on all the physical processes occurring in red giants in an effort to emphasize the interrelatedness of these individual processes, and to encourage a dia logue among experts that might serve to initiate a synthesis, or at least sharpen our understanding of the most important problems to address in the future."

"If simple perfect laws uniquely rule the universe, should not pure thought be capable of uncovering this perfect set of laws without having to lean on the crutches of tediously assembled observations? True, the laws to be discovered may be perfect, but the human brain is not. Left on its own, it is prone to stray, as many past examples sadly prove. In fact, we have missed few chances to err until new data freshly gleaned from nature set us right again for the next steps. Thus pillars rather than crutches are the observations on which we base our theories; and for the theory of stellar evolution these pillars must be there before we can get far on the right track. " These words written by Martin Schwarzschi1d in his famous book en titled "Structure and Evolution of the Stars"(1958) remind us how necessary and fruitful is the interplay of stellar evolution theory and observations. Clearly, observations are the great censor by their possibility of confirming or contradicting theoretical constructions. In addition, they have a driving role: new and sometimes unexpected facts may give rise to progressive ideas and stimulate further theoretical developments. In turn, theory, in its major role of sifting out and placing the facts in a logical sequence based on physical laws, must also be predictive and indicate new and pertinent observations to be undertaken."

Measuring the masses of galaxies as a function of redshift is perhaps one of the most challenging open issues in current astronomical research. The evolution of the baryonic and dark matter components of galaxies is not only a critical test of the hierarchical formation paradigm, but ultimately also provides new clues on the complex interplay between star formation, the cooling and heating of gas and galaxy merging processes.This book reviews current techniques to measure the baryonic (stellar) and dark masses of nearby galaxies, and focusses on ongoing attempts to measure these same quantities in galaxies at higher and higher redshifts. It also gives room to future perspectives, with special emphasis on new survey projects and satellite missions.

At close inspection every galaxy appears to have its own individuality.A galaxy can be warped, lop-sided, doubly-nucleated, boxy or disky, ... in its own specific, peculiar way. Hence, for a complete description, galaxy taxonomy may ask for finer and finer classification schemes. However, for some applications it may be more fruitful to let details aside and focus on some global properties of galaxies. One is then seeking to measure just a few quantities for each galaxy, a minimum set of globalobservables that yet captures some essential aspect of these objects. One very successful example of this approach is offered by the scaling rela tions of galaxies, the subject of the international workshop held at ESO head quarters in Garching on November 19-21, 1996. Discovered in the late 1970's, the Tully-Fisher relation for the spirals and the Faber-Jackson relation, or its more recent version the Fundamental Plane, for ellipticals have now become flourishing fields of astronomical research in their own right, as well as being widely used tools for a broad range of astronomical investigations. The work shop was designed to address three key issues on galaxy scaling relations, i.e., their Origins, Evolution, and Applications in astronomy. The Origins of galaxy scaling relations still escape our full understanding."

This symposium was dedicated to science opportunities with the VLT. All major areas of astronomical research were discussed in the plenary sessions, ranging from where we stand in cosmology to the new frontiers in the solar system. The workshops published in this volume focussed on different ways of finding clusters of galaxies at high redshift, on gravitational lensing by distant compact clusters, on the use of stellar populations as distance, age or abundance indicators, and on the extraordinary progress made in the discovery of extrasolar planets. This book affords a glimpse of what will be at the center of astrophysical research in the forthcoming decade. It is addressed to researchers and graduate students.

x about a sequence of reVlew lectures, each followed by contributed talks and discussions. The opening session was devoted to reviewing the most recent results concerning the determination of chemical abundances in particularly inte resting objects providing direct evidence for stellar nucleosynthesis (like planetary nebulae, supernovae and supernova remnants). In Session 2 recent results on some relevant nuclear reaction rates have been presented. Session 3 grouped the contributions concerning the quasi-static evolution of normal stars, its relevance for the nucleosynthesis of the varlOUS elements and isotopes, and the comparison of the evolutionary models with the observations. Session 4 addressed the important questions of identifying the precursors of both Type I and Type II supernovae, and of determining the detailed composition of the ejecta by explosive nucleosynthesis associated with these events. Finally, Session 5 was devoted to a presentation of recent calculations of the evolution of hypothetical pre-galactic very massive objects (in cluding their potential role in pre-galactic nucleosynthesis), and to reviewing the progress that has been made in understanding the chemical evolution of galaxies. The discussion during and after talks was spirited and contributed signi ficantly to the succes of the workshop. We regrett for not having been able of reporting it "in toto" in the proceedings. Nevertheless, we hope that what has been recorded may still give to the reader at least part of the excitement we have experienced during the ten days of the workshop."

In recent years, it has become clear that the red-giant phase is one of the most dramatic periods in a star's life, when all of its parts become involved in ways that have both direct and indirect observational consequences. This is most particularly true of low- and intermediate mass stars during the second ascent of the giant branch. Such stars bring to their surfaces products of nucleosynthesis currently taking place in their deep interiors, they pulsate as Mira variables, develop extended outward-flowing atmospheres that may exhibit maser properties, and shed great quantities of matter, sometimes highly processed, into the inter stellar medium. The manner in which processed matter is brought to the surface is far from being completely explained, and the precise mechanism or mechanisms whereby matter is ejected from the stellar surface (whether by deposition of Alfven waves, radiation pressure on grains, or as a consequence of so me large scale envelope instability) has yet to be elucidated to every one's satisfaction. The purpose of the second workshop in Astrophysics, organized by the "Advanced School of Astronomy," was to bring together experts on all the physical processes occurring in red giants in an effort to emphasize the interrelatedness of these individual processes, and to encourage a dia logue among experts that might serve to initiate a synthesis, or at least sharpen our understanding of the most important problems to address in the future."

This workshop was intended as an update and an extension of the workshop 011 the "Spectral Evolution of Galaxies" that was held in Erice two years ago. It concentrates 011 Ilew developments concerning galaxies seen at large look back times. This seemed also a good opportunity to look ahead to the next generation of ground- and space based instrumentation, and to consider various future strategies for collecting information concerning the edge of the observable universe. The main idea was to bring together people with specialities in modelling galaxy components (such as stars, clusters, gas, and dust) as well as whole stellar systems (stellar populations, star formation rates, chemical enrichment), and people specialized in making direct measurements of galaxies and clusters at large look back times. The confrontation of expectations and observations was planned to be the central theme of the conference, which explains the title "Towards Understanding Galaxies at Large Redshift." The first part of the workshop focussed on the physical processes that operate in galaxies, and that would likely have some observable manifestation at large redshifts. In the second part the most recent observational work was reported, and we were pleased to have the participation of most of the groups active in this field. The last part was directed towards new approaches to be made possible by the next generation of instrumentation, although in general all the contributions were indeed in this spirit of setting more ambitious goals."

Along with the traditional optical window, many new windows have been opened on galaxies in the last two decades, made possible by new developments in groundbased detectors and by space missions that allow detection of photons that are otherwise absorbed by the Earth's atmosphere. Galaxies can now be observed in the radio, submillimeter, IR, optical, UV, X- and gamma-ray bands, each window allowing us to learn more about galactic components and properties. These developments have also imposed the view that a deeper understanding of even normal galaxies requires a panchromatic approach, making use of all of the data gathered from the different windows to synthesize a comprehensive physical image of these complex astronomical systems. Windows on Galaxies presents a comprehensive view of galaxies through all the available windows, bringing together both theoretical and experimental approaches in the form of a series of reviews reporting the most recent developments complemented by contributed talks and discussions. TEXT NO. 2 The sixth workshop of the Advanced School of Astronomy examined galaxies through all available wavelength windows. Over the last twenty years, new wavelength windows have been opened in astronomy which have created many new possibilities for the observation of the properties of galaxies. The outcome of the meeting clearly stated that the approach towards the studying of galaxies should be panchromatic. Each window, from radio to gamma-rays, shows different components, and a synthesis of this knowledge presents astronomers with a comprehensive physical image of these astronomical systems: star formation, evolution of galaxies, molecular contents, gas flows, interstellar matter and properties of galaxies in the several wavelength fields are discussed in this volume.

As it was said by one of the participants to this workshop" In our attempts to understand the spectral evolution of galaxies, we are fortunate indeed to have the ability to look back in time and observe galaxies as they were billions of years ago. Perhaos in no other discipline is it possible to gain such a direct view to hJstory. The galaxies we seek to study are remote, their light faint, and thus only recently has it become technicaJlv feasible to sample the spectra of normal luminosity galaxies at lookback times of five billion years or more" .... or, perhaps. even to see galaxies in the process of their formation. or shortly afterwards. This fourth workshop organized by the "Advanced School ot Astronomy was indeed centered on the "Spectral Evolution of Galaxies." on reviewing and discussing the relevant astrophysical processes and on assessing our current ability to model and understand the evolution of stellar populations. Following an opening session dealing with some outstanding questions of galaxy evolution. Session I addressed the specific problems of galaxy and star formation processes. topics of uncertainty and controversy to which IRAS observations may give novel perspectives. The properties of stellar populations in the local group of galaxies formed the basis of Session II. Session III dealt with the fundaments of the theory of spectral and photometrical evolution of stellar populations. and with recent developments in the theory of stellar structure. a necessary step to model and understand galactic evolution.

In the development of Fundamental Physics on one side, and of Astronomy/Cosmology on the other side, periods of parallell, relatively independent progress seem to alternate with others of intense interaction and mutual influence. To this latter case belong the very beginnings of Modern Physics, with Galileo and Newton. There is now a widespread feeling that another of such flourishing periods may have started some ten years ago, with the advent of Unified Theories and the introduction of Inflationary Cosmologies. The interaction between the two disciplines has become tighter ever since, spurring studies of e. g. astronomical and particle Dark Matter candidates, Superstrings and Cosmic Strings, phase transitions in the Early Universe, etc. etc. Then the recent birth of Neutrino Astronomy has added further flavor to this splendid conjunction. It was indeed with the clear perception of this trend that six years ago CERN and ESO decided to jointly organize a series of symposia focusing on the interactions between Astronomy, Cosmology, and Fundamental Physics, to be held about every two years. The aim of these meetings is to bring together astronomers, cosmologists, and particle physicists to exchange information, to discuss scientific issues of common interest, and to take note of the latest devolopments in each discipline that are relevant to the other. The First ESO-CERN Symposium was held at CERN (Geneva) on November 21-25, 1983. Then for its Second edition the ESO-CERN Symposium moved to Garching bei Miinchen, where ESO headquarters are located, and took place on March 17-21, 1986.

This book is a synopsis of modern deep-field astronomy, based on the powerful telescopes and instruments developed in recent years. It is organized along topical themes, such as the extragalactic background radiation at different wavelengths, the evolution of galaxies, the history of star formation, the nature of absorbers, the reionization of the intergalactic medium, the validity of photometric redshifts, gravitational lensing, and clustering of galaxies. Stellar and substellar objects were not neglected, however, and one session was devoted to nearby bodies such as trans-Neptunian solar system objects, brown dwarfs, and stars with special characteristics.

One approach to learning about stellar populations is to study them at three different levels of resolution. First in our own Galaxy; secondly from nearby galaxies where stars can still be resolved; and thirdly in remote galaxies in which the stellar population can only be studied in integrated light. This IAU Symposium covered the entire range of galaxies in its study of their stellar populations. Interspersed with theoretical papers, the wealth of observational results provides an important state-of-the-art presentation of the progress that has been made in this field.

"If simple perfect laws uniquely rule the universe, should not pure thought be capable of uncovering this perfect set of laws without having to lean on the crutches of tediously assembled observations? True, the laws to be discovered may be perfect, but the human brain is not. Left on its own, it is prone to stray, as many past examples sadly prove. In fact, we have missed few chances to err until new data freshly gleaned from nature set us right again for the next steps. Thus pillars rather than crutches are the observations on which we base our theories; and for the theory of stellar evolution these pillars must be there before we can get far on the right track. " These words written by Martin Schwarzschi1d in his famous book en titled "Structure and Evolution of the Stars"(1958) remind us how necessary and fruitful is the interplay of stellar evolution theory and observations. Clearly, observations are the great censor by their possibility of confirming or contradicting theoretical constructions. In addition, they have a driving role: new and sometimes unexpected facts may give rise to progressive ideas and stimulate further theoretical developments. In turn, theory, in its major role of sifting out and placing the facts in a logical sequence based on physical laws, must also be predictive and indicate new and pertinent observations to be undertaken."