Since their first detection 15 years ago, radio recombination lines from several elements have been observed in a wide variety of objects including HII regions, planetary nebulae, molecular clouds, the diffuse interstellar medium, and recently, other galaxies. The observations span almost the entire range from 0.1 to 100 GHz, and employ both single djsh and aperture synthesis techniques. The theory of radio recombination lines has also advanced strongly, to the point where it is perhaps one of the best-understood in astro physics. In a parallel development, it has become possible over the last decade to study these same highly-excited atoms in the laboratory; this work provides further confirmation of the theoretical framework. However there has been continuing controversy over the astrophysical interpre tation of radio recombination line observations, especially regarding the role of stimulated emission. A workshop was held in Ottawa on 24-25 August, 1979, bringing together many of the active scientists to review the field and discuss these questions of interpretation. A broad concensus has emerged: the subtleties of the line-formation process are understood, and the conditions under which reliable in formation can easily be extracted from the line measurements are known. It thus appears likely that the emphasis will shift increasingly from the study of the line phenomenon itself to further application in other areas of astrophysics, ranging from physical processes in plasmas (temperatures, densities, ionization structure), to the large-scale properties of our galaxy (abundances, kinematics, structure), and studies of extragalactic systems."

Long-term measurements of field strength have been performed over a 160 km path entirely over sea in the Baltic area. For short periods the radio measurements have been combined with meteorolo- gical measurements in order to describe the structure of the re- fractive index field. The heigth of layers was continously deter- mined by remote sensing techniques and their thickness and inten- sity by airborne and balloonborne instruments. From these data, field strengths have been calculated for scatter, reflection and duct propagation. It will be shown that reflection propagation dominates at the low frequency end. Whilst at higher frequencies, very sharp layers are required for reflection propagation. At these frequencies, high signals are generally caused by duct propagation. 1.1 Instruments and plan for the experiments. The radio measurements were performed with the following equipment. 5000 MHz: Transmitted power 500 kW (pulsed). Reflector antennas. Free space field strength over the path + 15 dBm. 460 MHz: Transmitted power 10 W (CW) 8 element Yagi antennas. Free space field strength over the path - 65 dBm. 170 MHz: Transmitted power 10, W(CW). 8 element Yagi antennas. Free space field strength over the path - 60 dBm. The antenna heights for the transmitters and receivers were 100 m above sea level. The field strengths were recorded on ink recorders and simul- taneously sampled, digitized and evaluated on line in a minicom- puter. For the meteorological measurements, the following equipment were used: Airborne microwave refractometer and thermistor, flown up to 2000 m.

My interest in the history of the Struve family is long-standing but lay dormant until 1972, when I found myself organizing a symposium of the International Astronomical Union in memory of the second Otto Struve. To satisfy my own curiosity, I investigated the precise relationships of the famous astronomers in the family and published an account of them, based mainly on secondary sources. The exercise made me a ware that there was no biography in English of the first and probably still the greatest astronomer in the clan - Friedrich Georg Wilhelm Struve. Wilhelm's son, the first Otto, wrote an account (in German) of his father's life, intended primarily for family and close friends and --though printed-- not generally available. Through the kindness of a family member I have a copy from which I have been able to work. The Soviet historian of science, Z. K. Sokolovskaya, wrote a biography in Russian, in 1964, to mark the centenary of Wilhelm's death. This had a limited edition, and my efforts to obtain a copy failed. Neither work has, in its entirety, been translated into English, although Michael Meo of Oakland, California, and Kevin Krisciunas of Hilo, Hawaii, have kindly made available to me their unpublished translations of some sections of the latter. In the of a complete copy, however, when I decided to attempt an English absence language biography, I thought it best to do so independently of Sokolovskaya's."

Scientists in the late twentieth century are not the first to view galaxy formation as a phenomenon worthy of explanation in terms of the known laws of physics. Already in 1754 Kant regarded the problem as essentially solved. In his Univerlal Natural Hutory and Theory 0/ the H eaven$ he wrote; "If in the immesurable space in which all the suns of the Milky Way have formed themselves, we assume a point around which, through some cause or other, the first formation of nature out of chaoo began, there the largest mass and a body of extraordinary attraction will have arisen which has thereby become capable of compelling all the systems in the process of being formed within an enormous sphere around it, to fall towards itself as their centre, and to build up a system around it on the great scale . . . . Observation puts this conjecture almost beyond doubt. " More than 200 years later, a similar note of confidence was voiced by Zel'dovicb at an IAU symposium held in Tallin in 1911; "Extrapolating . . . to the next symposium somewhere in the early eighties one can be pretty sure that the question of the formation of galaxies and clusters will be solved in the next few years. " Perhaps few astronomers today would share Kant's near certainty or feel that Zel'dovich's prophecy has been fulfilled, Many, however, will sympathize with the optimistic olltlook of these two statements.

This volume is the documentation of the first Course on 'Neutron Stars, Active Galactic Nuclei and Jets', of an Erice School with a wide astro physical scope. The choice of the subject was made because of an apparent similari ty - stressed already at earlier meetings - of four classes of astrophy sical jet sources: Active Galactic Nuclei, Young Stellar Objects, Binary Neutron Stars and Binary White Dwarfs. They share important properties such as their morphology, high variability and large veloci ty gradients as well as - with some inference - their broad spectrum, hypersonic outflow and core/lobe power ratio. Despite this apparent similarity of the four source classes, quite different models have been put forward for their description: (i) The central engine of active galactic nuclei has been generally thought to be a black hole, in contrast to the central engine of young stellar objects and cometary nebulae which apparently is a pre-T-Tauri star, some six orders of magnitude less compact, and to the central engine of planetary nebulae which mayor may not be a binary white dwarf. (ii) The elongated lobes, or flow patterns, have been often interpreted as highly directional stellar wind outflows whereas in a few well mapped cases, the elongated flow appears to be 'pumped up' through a much narrower channel, or jet, both in the extragalactic and stellar sources.

Stellar mass loss is an essential part of the cycling of material from the interstellar medium into stars and back, and must be understood if we are to model processes on galactic to cosmological scales. The study of stellar winds and the effects of stellar mass loss has reached a particularly exciting stage where observational capabilities are increasingly able to provide interesting constraints on models and theories. Recent resu1ts from theoretical and observational work for both hot and cool stars with substantial winds have led to the suggestion that a combination of pulsation with other mechanisms makes for particularly efficient mass loss from stars. This provided the original motivation for the organization of this workshop. The conference was organized along relatively conventional lines according to the types of objects being scrutinized. However the true unity of the proceedings comes from the interplay of the mechanisms involved. For example, for the cool, luminous Mira variables, pulsation leads to shock waves that extend the atmosphere, enhancing dust formation; radiation pressure on dust drives the wind, cooling the atmosphere and in some cases suppressing the shocks. Similarly for the Be stars, both pulsation (in this case, non-radial) and radiation pressure (due to UV resonance lines) are expected to be important, and this expectation is at least qualitatively borne out by the observations.

Over the last decade we have witnessed a rapid change in our understanding of the late stages of stellar evolution. A major stimulus to this has been the synthesis of observational data from different wavebands of the electromagnetic spectrum. The advent of infrared astronomy has led to the discovery of many luminous. late-type stars obscured by their circumstellar dust envelope. Sources discovered in the IRC and AFGL infrared sky surveys were followed up by radio observa tions, leading to the widespread use of the OH and CO molecules as probes of the circumstellar envelopes. Advances in the technique of aperture synthesis have made possible observations with unprecedent resolving power, both in spectral-line and continuum. The success of the recent IRAS sky survey, with the detection of over 250,000 sources, brings the promise of even more exciting years ahead. This area of astronomical research is also blessed with the close collaboration between theorists and observers. New ideas are constantly being quantitatively tested by new data. Theoretical predictions are eagerly used as guides for further observations. This conference was initiated with the following objective: bring together workers in optical, infrared, radio and theoretical astronomy and let them confront each other. Based on the post-conference res ponses we received, many of the participants have indeed found this Workshop a stimulating experience. The Workshop on the Late Stages of Stellar Evolution was held from 2-5 June 1986 in Calgary, Canada."

The I. A. U. Colloquium No. 29 was held in Budapest, September 1-5, 1975. The subject of the colloquium was: "Multiple Periodic Variable Stars". The colloquium was organized by the Scientific Organizing Committee consisting of W. S. Fitch (Chairman), M. W. Feast, B. V. Kukarkin, P. Ledoux, J. Smak, R. S. Stobie, B. Szeidl, B. Warner and S. C. Wolff. The local organization was placed in the hands of a Committee consisting of the staff of the Konkoly Observatory: B. Szeidl (Chairman), K. Barlai, M. Ill, S. Kany6 and L. Szabados. The colloquium was attended by about 90 scientists representing Australia, Austria, Belgium, Bulgaria, Canada, Czechoslovakia, Denmark, France, F. R. G. , G. D. R. , Greece, Hungary, India, Ireland, Italy, Japan, The Netherlands, New Zealand, Poland, Roumania, South Africa, United Kingdom, U. S. A. and U. S. S. R. Eight sessions were held, viz. 1. . p Canis Majoris Stars. Chairman: W. Wenzel 2. Magnetic and Ap Variables. Chairman: S. C. Wolff 3. Miras and Red Variables. Chairman: P. R. Wood 4. Cepheids. Chairman: R. S. Stobie 5. RR Lyrae Stars. Chairman: B. Szeidl 6. RRs and {) Scuti Stars. Chairman: W. S. Fitch 7. White Dwarfs and Novae. Chairman: B. Warner 8. Close Binaries and X-Ray Sources. Chairman: E. H. Geyer At the beginning of the first session a welcome was presented by Professor G.

I - PRIMORDIAL NUCLEOSYNTHESIS 1 --. -~-~----,---,-. --------- H. Reeves Primordial nucleosynthesis in 1985 3 The puzzle of lithium in evolved stars H. Reeves 13 High energy particles in dark molecular H. Reeves clouds 23 P. Delbourgo-Salvador, G. Malinie, J. Audouze Standard big bang nucleosynthesis and 3 chemical evolution of D and He 27 G. steigman, D. S. P. Dearborn, D. N. Schramm The survival of Helium,3 in stars 37 G. steigroan How degenerate can we be ? 45 J. Audouze, D. Lindley, J. Silk 3 Early-photoproduction of D and He and pregalactic nucleosynthesis of the light elements 57 R. Schaeffer, P. Delbourgo-Salvador, J. Audouze Influence of quark nuggets on primordial nucleosynthesis 65 T. P. Walker, E. W. Kolb, M. S. Turner Primordi. al nucleosynthesis with generic part. icles 71 D. N. Schramm Dark matter and cosmological nucleosynthesis 79 B. J. Carr Nucleosynthetic consequences of population [II stars W. Glatzel 87 vi CONTENTS 95 I I -EXPWSIVE OBJECTS J. W. Truran Nucleosynthesis accompanying classical nova outbursts 97 M. Wiescher, J. GOrres, P. -K. Thielemann, H. Ritter Reaction rates in the RP-process and nucleosynthesis in novae 105 Type I supernovae ll3 J. C. Wheeler R. canal, J. lsern, J. Labay, R. Lbpez Nucleosynthesis and type I supernovae 121 P. -K. Thielemann, K. Nomoto, K. Yokoi EXplosive nucleosynthesis in carbon deflagration models of type I supernovae 131 E. Mi. iller, Y. Eriquchi Differentially rotating equilibrium models and the collapse of rotating degenerate configurations 143 S. E. WOOsley, T. A.

Historically, the discovery of tools, or evidence that tools have been used, has been taken as proof of human activity; certainly the invention and spread of new tools has been a critical marker of human progress and has increased our ability to observe, measure, and understand the physical world. In astronomy the tools are telescopes and the optical and electronic instruments that support them. The use of the telescope by Galileo marked the beginning of a new and productive way to study and understand the universe in which we live. The effects of this new tool on what we can see, and how we see ourselves, are well known. However, after almost four centuries of developing ever more sensitive and subtle instruments as tools for astronomy, it might have been expected that only a few minor improvements would remain to be made, or that possibly the law of diminishing returns would have taken effect. On the contrary, the new instruments and ideas for new instruments described in this book make it clear that the rate of progress has not diminished, and that this subject is still as exciting and productive as ever. Instrumentation for Ground-Based Optical Astronomy was chosen as the theme for the Ninth Santa Cruz Summer Workshop in Astronomy and Astrophysics.

P. J. MESSAGE University of Liverpool The papers which comprise this volume were presented at Colloquium No. 41 of the International Astronimical Union, which was held in Cambridge, England, from the 17th to the 19th of August, 1976, and had as its subject 'Dynamics of Planets and Satellites and Theories of their Motion'. The Colloquium was held just prior to the XVIth General Assembly of the Union (which was held from 24th August to 2nd September, in Grenoble, France) to provide an opportunity for the presentation of research papers on a number of active and lively branches of Celestial Mechanics to a gathering of experts in the field, and for the stimulus of discussion of research problems of interest to participants. A number of papers testify to the progress being made in General Planetary Theory, the theories of motion of the minor planets, the Moon, and the satellites of Jupiter and Saturn, and to significant advances in both the general and restricted gravitational problems of three bodies. The Organizing Committee of the Colloquium was comprised of J. Chapront, R. L. Duncombe, J. Hadjidemetriou, Y. Kozai, B. Morando, J. Schubart, V. Szebehely, and P. J. Message (Chairman). The local Organizer was D. C. Heggie, to whose tireless efforts the success of the arrangements is due. IX LIST OF PARTICIPANTS N. Abu-el-Ata, Bureau des Longitudes, 77 Avenue Denfert Rochereau, 75014 Paris, France K. Aksnes, Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, U. S. A.

Although there are, in addition to the classic but somewhat dated books'l-, some excellent recent books on ionospheric physics and aeronomy'l-..., their scope is quite different from that of the present monograph. This monograph concentrates on the fundamental physical and chemical processes in an idealized planetary ionosphere as a general abstraction, with actual planetary ionospheres representing special cases. Such an approach appears most appropriate for a concise in troduction to the field, at a time when increasing experimental in formation on the ionospheres of other planets can be anticipated. The main purpose of this monograph, in line with that of the whole series, is to appraise where we stand, what we know and what we still need to know. It is mainly addressed to graduate students and researchers who are in the process of getting acquainted with the field. Within the scope of this monograph it would be impossible to do justice to all relevant publications. Hence, references are somewhat selective and largely limited to the more recent original papers and to authoritative reviews, the latter generally providing also detailed references regarding the historical development of the particular topic. Cgs (gaussian) units are generally used in this book, except where practical units are more appropriate. This book has evolved from a graduate course of the same title which I gave at the Catholic University of America, Washington, D. C."

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.

Text no 1 Radio Recombination Lines (RRLs), discovered in the USSR in 1964, have become a powerful research tool for astronomers. Available throughout the radio spectrum, these lines carry information regarding the density, temperature, turbulence and velocity of thermal plasmas. Their very existance shows the presence of thermal gas. They also can carry information regarding magnetic fields if Zeeman splitting were to be detected. Containing the proceedings of an IAU Colloquium celebrating the 25th anniversary of their detection, this volume tells us what has happened since. It contains the story of the detection of RRLs and reviews of many areas of physics of the interstellargas from which stars form, HII regions excited by newly formed stars, planetary nebulae involving dying stars, and the structure of our Milky Way and other galaxies reflecting the large-scale morphology of the star formation process. In addition there is an article describing modern laboratory studies of Rydberg atoms to probe the basic physics of atomic structure, and articles describing the theory of collisions and radiation upon Rydberg atoms leading to observate effects to be used as diagnostic tools in astromony. This book focuses on the 25 years of astronomical research with radio recombination lines (RRLs) since their discovery in 1965. It covers a wide range of topics: papers dealing with research into Rydberg atoms both in the laboratory and in the interstellar medium of our galaxy and others; papers on the interaction of radiation and atomic systems, as well as with the effects of inadiabatic collisions between these atoms and both ions and electrons. It deals with astronomical observations of atoms with `diameters' ranging from 0.08 to 50 mum a size factor of 625. It deals with RRLs in absorption, in emission and as true masers. And it deals with plasmas with temperatures ranging from 10 to greater than 104 kelvins, and with an even greater range of volume densities. Much new work is reported, including low frequency RRLs discovered in 1980 and the maser RRLs from the star MWC349, discovered in 1989. The advent of aperture synthesis telescopes and large single-element telescopes have made possible RRL studies with high angular resolution. The sum total of the work reported here will make the volume a platform from which to search new horizons in RRL research.

7 Hydrodynamic Instabilities in Close Binary Systems (Frederic A. Rasio) 121 7. 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . 121 7. 1. 1 The stability of self-gravitating fluid equilibria 121 7. 1. 2 Astrophysical motivation . 123 7. 1. 3 Common envelope systems 125 7. 2 Dynamical instabilities. . . . . . . 126 7. 2. 1 Physical mechanism . . . . 126 7. 2. 2 Application to coalescing neutron star binaries 127 7. 3 Secular instabilities. . . . . . . . . . . 130 7. 3. 1 Physical mechanism . . . . . . 130 7. 3. 2 Application to contact binaries 133 8 Common Envelope Evolution in Binary Systems (Mario Livio) 141 8. 1 Introduction. . . . . . . . . . . . . . . . . . . . 141 8. 2 The entrance into the common envelope phase . . . . . 142 8. 3 The outcome of the CE phase. . . . . . . . . . . . . . . 145 8. 4 How close can we get to observing the common envelope Phase? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 8. 4. 1 How can PNe with binary nuclei be used to constrain CE physics . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 8. 4. 2 How can nova systems be used to constrain CE physics 148 8. 4. 3 Other tests of common envelope evolution 150 8. 5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 151 9 Structure and Evolution of Massive Close Binaries (Dany Vanbeveren) 155 9. 1 Introduction. . . . . . . . . . . . . . . . . . 155 9. 2 Definitions. . . . . . . . . . . . . . . . . . . 156 9. 3 Intermediate mass and massive single stars 156 9. 3. 1 Observations . . . . . . . . . . . . . 156 9. 3. 2 Stellar structure equations for non-rotating IMS's and MS's 160 9. 3. 3 Evolutionary computations of non-rotating IMS's and MS's 162 9. 3. 4 Overall comparison with observations '" 163 9. 3. 5 The role of rotation in single star evolution . . .

Much has been said and written about the abilities of modern instrumentation to help solve problems of combustion in engines. In the main, however, the design and fabr ication of combustion chambers continues to be based on extrapolation of exper ience gained from use and rig tests, with little input from advanced techniques such as those based on optical diagnotics. At the same time, it has become increasingly difficult to design better combustion chambers without knowledge of the relevant flow processes. Thus, the future must involve improved understanding which, in turn, will require detailed measurements of velocity, temperature and concentration. The need to narrow the gap between current industrial practice and the acquisition and implementation of improved techniques motivated the organization of the Advanced Study Institute upon which this volume is based. This Institute on Instrumentation for Combustion and Flow in Engines was arranged to display the needs of industry and the possibilities made available by modern instrumentation and, at the same time, to make clear the relative advantages of optical and probe techniques. Held at Vimeiro during the period from 13 to 26 September, 1987, the Institute was attended by 120 participants and 16 invited lecturers.

SOHO, the Solar and Heliospheric Observatory, is a project of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, and the solar wind. To achieve its scientific goals it carries a complement of twelve sophisticated, state-of-the-art instruments. Three helioseismology instruments are expected to provide unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone. A set of five complementary remote sensing instruments, consisting of EUV and UV imagers, spectrographs and coronagraphs, will give us our first comprehensive view of the outer solar atmosphere and corona, leading to a better understanding of the enigmatic coronal heating and solar wind acceleration processes. Finally, three experiments will complement the remote sensing observations by making in-situ measurements of the composition and energy of the solar wind and charged energetic particles. This volume contains detailed descriptions of all the twelve instruments on board SOHO. Also included are an overview paper and a description of the SOHO ground system, science operations and data products. The aim of these papers is to make the broader scientific community, and in particular potential guest investigators, aware of the scientific objectives and capabilities of the SOHO payload and to provide a reference document for the various instruments.

The near Infra-Red emission of the Interstellar Medium is a very puzzling subject. In the brightest regions, where spectroscopic observa tions are possible from the ground, several bands (3.3 - 3.4 - 6.2 - 7.7 - 8.6 - 11.3 ~m) have been observed since 1973. The absence of satisfying explanation was so obvious that they were called "Unidenti fied IR Emission Bands". The puzzle still increased when were known the first results of the general IR sky survey made by the satellite IRAS. On a large scale, the near IR emission of the Interstellar medium was expected to be very small but it was observed to be about one third of the total IR emission for our own galaxy ..* The situation has moved in 1984 when it was suggested that a class of stable organic molecules, the Polycyclic Aromatic Hydrocarbons (PAH's) could be at the origin of this near IR emission. Initially based on the required refractory character of particules that should be heated to high temperature without subliming, this hypothesis leads to a sugges tive spectroscopic similarity with the observed astronomical bands. This hypothesis is attractive and it has many implications, for ins tance, the PAHs would be the most abundant organic molecules in the universe. However, many points have to be clarified and the different consequences of this suggestion should be explored.

The words of this preface were written when the book was ready to go to the press; and are limited to only a few points which are best made in this place. As is intimated by the sub-title, the whole volume was written with appli cations in mind to double-star astronomy. The latter is, however, not the only branch of our science which could benefit from its contents. The same is true of certain aspects of the dynamics of stellar systems or galaxies (the stellar popula tions of which are also characterized by the fact that the mean-free-path of their constituent stars are long in comparison with the dimensions of the respective systems); the central condensations of which are high enough to approximate the gravitational action of a "mass-point." This fact did not, to be sure, escape the attention of previous investigators (in the case of globular clusters, in particular, the Roche model was introduced in their studies under the guise of polytropic models characterized by the index n = 5); though no particular attention will be paid to these in this book. But possible applications of the Roche model are not limited to problems arising in stellar astrophysics. With Coulomb forces replacing gravitation, the equilibrium model finds a close analogy in the field of electrostatics-as was pointed out already at the beginning of this century by (then young) J. H. Jeans (cf."

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.

The visible universe is a small perturbation on the material universe. Zwicky and Sinclair Smith in the 1930s gave evidence of invisible mass in the Coma and Virgo Clusters of Galaxies. Better optical data has only served to confound their critics and the X-ray data confirms that the gravitational potentials are many times larger than those predicted on the basis of the observed stars. Dynamical analyses of individual galaxies have found that significant extra mass is needed to explain their rotational velocities. On much larger scales, tens of megaparsecs, there is suggestive evidence that there is even more mass per unit luminosity. What is this non-luminous stuff of which the universe is made'? How much of it is there? Need there be only one kind of stuff? There are three basic possi bili ties:- all of it is ordinary (baryonic) matter, all of it is some other kind of (non-baryonic) matter, or some of it is baryonic and some is non-baryonic.

The International Heidelberg Workshop on TeV Gamma-Ray Astrophysics' brought together astrophysicists from the various fields which play a role in the formation of high energy gamma-ray emission. In particular, theoretical and observational aspects of the physics and astrophysics of pulsars and quasars, the acceleration of particles at Supernova Remnants and other strong astrophysical shock fronts, and cascade processes in universal background photon fields were comprehensively discussed in more than thirty reviews by leading experts. In their entirety these reviews describe the birth of a new field of astronomy. This field concerns cosmic gamma-rays of very high energy which are observed with ground-based optical telescopes due to the Cherenkov emission of the secondary particles created by the interaction of these gamma-rays with atoms in the Earth's atmosphere. Beyond that, the workshop encompassed the latest developments and trends in theory and observation of cosmic gamma-ray sources of all energies, from nuclear gamma-ray lines in the MeV-region, through the Bremsstrahlung, Inverse Compton, and pion decay continuum emission, to gamma-rays due the decay of exotic relics from the early Universe. Audience: Specialists as well as students in physics and astrophysics and young research workers.

This book deals with the fundamentals of stellar interferometry with emphasis on aperture synthesis using sparse array of telescopes particularly at optical/IR wavelengths, the origin, properties, and optical effects of turbulence in the Earth's atmosphere, techniques developed to overcome image degradation. Studded with more than one hundred and fifty illustrations and tens of footnotes, it addresses the basic tricks of trade, current trend, motivation, methods, and path to future promise of true interferometry both from the ground and space. Also discussed are the technical challenge involved, such as beam transportation and recombination, detecting fringes using modern sensors, and image synthesis. Astronomical science that benefits from aperture synthesis imaging are highlighted as well.

I. COSIIIC GAMMA RAYS AIm COSIIIC DUnmos L. Scarsi GAMMA RAY ASTRONOMY -- AN OVERVIEW OF THE GALACTIC DIFFUSE EMISSION: THE ORIGIN AND CONFINEMENT OF COSMIC RAyS ************ 1 P. L. Biermann PHOTON AND NEUTRINO-EMISSION FROM SHOCKWAVES IN ACTIVE GALACTIC NUCLE I ************************************************* 21 T. Stanev PRODUCTION OF ENERGETIC GAMMA-RAYS AND NEUTRINOS AT BINARY SySTEMS *********************************************** 3 9 F. W. Stecker COSMIC GAMMA-RAYS AND COSMIC-RAY NEUTRINOS FROM GALACTIC AND SOLAR DARK MATTER ANNIHILATION ****************************** 49 E. P. Liang GAMMA RAYS FROM CYGNUS X-I: NEW DIAGNOSTICS FOR A BLACK HOLE ******** 73 F. W. Stecker GAMMA-RAY ASTRONOMY AND THE HOLISTIC GALAXY ************************* 85 A. W. Wolfendale THE NEUTRINO SIGNAL FROM SNI987A *********************************** 12I A. E. Chudakov, Ya. S. Elensky and S. P. Mikheyev ON THE SPECTRUM OF NEUTRINOS FROM SNI987A ************************** 13I L. V. Volkova A COMMENT ON v Iv RATIO IN ATMOSPHERIC NEUTRINO FLUXES ************ 139 e 1I L. V. Volkova FLUXES OF MUONS AND NEUTRINOS GENERATED BY PRIMARY RADIATION IN THE MOON ****************************************** 141 viii P. I. Krastev and S. T. Petcov THREE-NEUTRINO OSCILLATIONS IN THE EARTH: RESONANCE AMPLIFICATION AND T-VIOLATION EFFECTS ************************** 145 A. E. Chudakov VHE AND UHE GAMMA RAY ASTRONOMY: HISTORY AND PROBLEMS ************** 163 G. B. Yodh ULTRA HIGH ENERGY ASTRONOMY **************************************** 183 A. E. Chudakov, G. Navarra and V. A. Tizengauzen ON THE 100 TeV UHE GAMMA-RAY DATA FROM CYGNUS X-3 AND HERCULES X-1 IN 1986 *************************************** 211 G. B.

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.