Summary of the NATO Advanced Research Workshop on Physical Signatures of Magnetospheric Boundary Layer Processes T A POTEMRA, M I PUDOVKIN, R W SMITH, V M VASYLIUNAS and A EGELAND 451 PREFACE These proceedings are based on the invited talks and selected research reports presented at the NATO Advanced Workshop on "PHYSICAL SIGNATURES OF MAGNETOSPHERIC BOUNDARY LAYER PROCESSES", held at Sundvolden Hotel, Norway, 9.-14.May 1993. The international political and scientific communities have gradually realized that the Earth's environment is more fragile than previously believed. This has led to the establishment of international research programmes directed toward the understanding of "Global Change". The Earth's magnetosphere, "the Earth-space", is a part of our environment, and physical processes in the magnetosphere and coupling between the solar energy stream, the solar wind, and the Earth-space are important in the complete understanding of our environment. Variations in the electromagnetic and particle energy output of the Sun have a significant effect on global changes. The energy transfer mechanisms at the days ide magnetospheric boundary layers and their ionospheric signatures are perhaps even more important to solar terrestrial research than the night-side processes in this connection. The dayside boundary layers and the polar cusps are the Earth's windows to outer space. The present NATO ARW was the latest in a series of conferences focused on dayside magnetospheric phenomena. It is five years since the preceding Workshop on "Electromag netic Coupling in the Polar Clefts and Caps" was held at Lillehammer in September 1988.

We are well aware of how dust influences our observations of distant stars and how easily dust may mislead us with regard to the way in which stars are distributed within the Galaxy, but how does dust affect our view of other galaxies? This is the question that was posed to those who attended this meeting. By its very nature dust is illusive: as dust obscures by both scattering and absorption, it can effectively disguise its very own existence. It was not until the mid-1930's that astronomers generally agreed that dust did redden and dim stars in our own Galaxy, and it was not until the late 1950's that astronomers began to seriously inquire of its effects in other galaxies To the best of our knowledge, this is the first international meeting to have been held devoted solely towards understanding the observational effects of dust in other galaxies. Because of this we have been fortunate in attracting many of the major workers in this field, both observers and theorists. Among these pages the reader will find a wide range of opinion about how much dust there is in the disks of galaxies, where that dust is, and how to model the effects of dust. We tried to structure this meeting so that there was a ready and easy exchange between the speaker and the audience, and so that there was a large amount of time for discussion.

Accretion disks in astrophysics represent the characteristic flow by which compact bodies accrete mass from their environment. Their intrinsically high luminosity, and recent progress in observational accessibility at all wavelength bands, have led to rapidly growing awareness of their importance and made them the object of intense research on widely different scales, ranging from binary stars to young stellar objects and active galactic nuclei. This book contains the proceedings of the NATO Advanced Workshop on `Theory of Accretion Disks 2' for which some of the most active researchers in the different fields came together at the Max-Planck-Institut for Astrophysics in Garching in March, 1993. Its reviews and contributions give an up-to-date account of the present status of our understanding and provide a stimulating challenge in discussions of open questions in a rapidly developing field.

The study of white dwarfs has been steadily growing during the last years and now is a mature field extending its influence over many others. Since white dwarfs are long lived objects, they can be used to obtain information about the history of the Galaxy. The simplicity of their structures enables them to act as precise particle physics laboratories and the extreme con ditions reached at their surfaces allow us to test the equation of state and to study the behavior of matter under conditions impossible to be reached in terrestrial laboratories. Nevertheless, white dwarfs are still challenging astrophysicists. Many questions, ranging from the determination of funda mental parameters to the evolution of their outer layers, are still waiting for a satisfactory answer. The European Workshop series on White Dwarfs started in 1974 as a con sequence of the effort and enthusiasm of Professor Volker Weidemann. The existing proceedings of these meetings, together with those corresponding to the lAU Colloquia held in Rochester (1979) and in Hanover (1988), provide a unique opportunity to follow the development of this field. We hope that the present volume will provide a representative snapshot of the state of the art in 1996. In this sense we are very indebted to all the participants that have sent their contributions according to the instructions (this clearly excludes everybody beyond three sigmas from the standards).

This monograph is the first to develop a mathematical theory of gravitational lensing. The theory applies to any finite number of deflector planes and highlights the distinctions between single and multiple plane lensing. Introductory material in Parts I and II present historical highlights and the astrophysical aspects of the subject. Part III employs the ideas and results of singularity theory to put gravitational lensing on a rigorous mathematical foundation.

An up-to-date presentation of the progress and current problems in the early universe, cosmic microwave background radiation, large scale structure formation, and the interplay between them. The emphasis is on the mutual impact of fundamental physics and cosmology, both at theoretical and experimental (observational) levels within a deep, well- focused and well-defined programme. The nature of the domain itself leads to different aspects, approaches and points of view on the same topic. Special care has been taken to provide the reader the basis of the different, sometimes competing lines of research. All contributions are uniformly excellent, with a careful selection of the subjects and approaches covered, presenting a unifying and rigorous view of the field. Audience: experimentalists and theoreticians from a variety of backgrounds: physics, astrophysics and astronomy. An excellent reference for post-doctoral scientists. Useful for senior scientists and advanced graduate students.

Magnetic energy release plays an important role in a wide variety of cosmic objects such as the Sun, stellar coronae, stellar and galactic accretion disks and pulsars. The observed radio, X-ray and gamma-ray emission often directly results from magnetic flares', implying that these processes are spatially fragmented and of an impulsive nature. A true understanding of these processes requires a combined magnetohydrodynamical and plasma physical approach. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics provides a comprehensive, interdisciplinary summary of magnetic energy release in the Sun and stars, in accretion disks, in pulsar magnetospheres and in laboratory plasmas. These proceedings include papers on both theoretical and observational aspects. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics is for researchers in the fields of solar physics, stellar astrophysics and (laboratory) plasma physics and is a useful resource book for graduate level astrophysics courses.

Since its launch in 1991, the Yohkoh satellite has been returning unprecedented observations of solar flares and the dynamic solar corona. This book is a collection of papers presented at a meeting held in: Yoyogi, Tokyo, on the occasion of Yohkoh's fifth anniversary of operation. The papers constitute a summary of observations and results over the five years, including contributions based on data from Yohkoh's hard and soft X-ray telescopes and its spectrometer experiments. The five years of data, covering approximately one-half of a solar cycle, reveal a fresh perspective on solar science, with a new picture of solar flares and the active Sun emerging. Also, for the first time there are extensive results from Yohkoh observations of the Sun during the solar minimum period. This wide-ranging volume will be of interest to workers in solar physics and X-ray astronomy. It also contains material appropriate for supplemental reading for graduate students in solar physics.

The Workshop "Optical Detectors for Astronomy" was held during October 8-10, 1996 at the headquarters of the European Southern Observatory in Garching, Germany. This was the third meeting of its kind, previous meetings being held in 1991 and 1993, but this is the first ESO "CCD Workshop" that has published proceedings. Most of the leading manufacturers and major astronomical observatories were represented, with the 117 attendees coming together from 14 different countries that spanned every continent on Earth. The motivation for the ESO CCD Workshop series is the creation of informal and open venue of information exchange about astronomical CCD detectors and systems. Judging from the reaction and feedback of the participants, the 1996 workshop was as successful as the previous editions, which is a credit to all who attended. The Workshop was organized as a mixture of invited talks, oral presentations, poster sessions and roundtable discussions, the latter used to foster a free exchange of ideas among participants. These technical sessions were complemented by an opening reception and a congenial evening in downtown Munich, which included a walking tour of the historic area followed by dinner at the famous Franziskaner brewery and an after dinner talk by Walter Kosonocky, who reviewed the history of CCD technology.

The IAU Colloquium No. 143 "The Sun as a Variable Star: Solar and Stellar Irradiance Variations" was held on June 20 - 25, 1993 at the Clarion Harvest House, Boulder, Colorado, USA. The main objective of this Colloquium was to review the most recent results on the observations, theoretical interpreta tions, and empirical and physical models of the variations observed in solar and stellar irradiances. A special emphasis of the Colloquium was to discuss the results gained on the climatic impact of solar irradiance variability. The study of changes in solar and stellar irradiances has been of high interest for a long time. Determining the absolute value of the luminosity of stars with different ages is a crucial question for the theory of stellar evolu tion and energy production of stellar interiors. Observations of the temporal changes of solar and stellar irradiances - in the entire spectral band and at different wavelengths - provide an additional tool for studying the physical processes below the photosphere and in the solar- stellar atmospheres. Since the Sun's radiative output is the main driver of the physical processes with in the Earth's atmosphere, the study of irradiance changes is an extremely important issue for climatic studies as well. Climatic models show that small, but persistent changes in solar irradiance may influence the Earth's climate.

The Medieval Warm Period and the Little Ice Age are widely considered to have been the major features of the Earth's climate over the past 1000 years. In this volume the issue of whether there really was a Medieval Warm Period, and if so, where and when, is addressed. The types of evidence examined include historical documents, tree rings, ice cores, glacial-geological records, borehole temperature, paleoecological data and records of solar receipts inferred from cosmogenic isotopes. Growth in the availability of several of these types of data in recent years, and technical advances in their derivation and use, warrant this state-of-the-art re-examination of Medieval Warm Period. The book will be of value to all those with an interest in the natural variability of the climate system, for example those concerned with anticipating and detecting anthropogenic climate change.

Long-term monitoring is of fundamental significance in solving many important problems in astrophysics and, furthermore, has unequalled value in extending observational runs with small telescopes for the education of young astronomers in order to teach them how to secure high-quality observational data over many years. The Impact of Long-Term Monitoring on Variable Star Research contains reports based on the analysis of data collected in the visible, IR and radio measurement ranges, as well as the design and history of well known photometric systems. Though the reporting of novel results forms an important part of the book, there are also reports of eight discussion sessions covering more general areas, such as extinction monitoring, the problems of archival storage of astronomical data, service observation, the role played by long-term monitoring in graduate teaching and thesis supervision, the interplay between the great observational effort and theory, the contribution of LTM to new knowledge of fundamental data, and the increasing decommissioning of telescopes of modest aperture.

The nonlinear theory of oscillating systems brings new aspects into the study of variable stars. Beyond the comparison of linear periods and the estimate of stability, the appearance and disappearance of possible modes can be studied in detail. While nonlinearity in stellar pulsations is not a very complicated concept, it generally requires extensive and sometimes so phisticated numerical studies. Therefore, the development of appropriate computational tools is required for applications of nonlinear theory to real phenomena in variable stars. Taking trends in variable star studies into consideration, the International Astronomical Union organized a colloquium for the nonlinear phenomena of variable stars at Mito, Japan in 1992. The colloquium served to give an overview of the new frontiers of variable star studies and to encourage further development of this field. The colloquium covered the fundamental theory, interesting observational facts, and the numerical modeling. The publication of the proceedings was somewhat delayed since one of the editors, M. T., was overwhelmed by administrative work. We are sorry that the excellent reviews of Drs. H. :Mori, M. Sano, and K. Makishima cannot be found in the proceedings. We also miss the summary given by Dr. W. W. Dziembowski. Throughout the editing procedure Dr. Y. Tanaka of Ibaraki University kindly helped us. Because of the unfortunate delay of the publication~ the significance of several papers may be affected. Even so, we believe that the papers are useful to variable star researchers because of their scientific importance.

This interdisciplinary book consists of the proceedings of the Alexander Ivanovich Oparin lOOth Anniversary Conference, The Third Trieste Conference on Chemical Evolution, which took place at the International Centre for Theoretical Physics from 29 August till 2 September, 1994. A general overview of Oparin's life and work is followed by a review of Alfonso Herera, another pioneer in the studies of the origin of life. The subject matter is organized in ten sections corresponding to various aspects of our current understanding of the subject that was initiated by Oparin. These subjects were covered by fifty three speakers. There were sixty seven participants from a wide geographical distribution; twenty seven countries were represented. We have included the invited lecture of Professor Igor Kulaev, who was unable to be present at the conference for reasons beyond his control. The conference was generously supported by the International Centre for Theoretical Physics, the Commission of the European Communities, the International Centre for Genetic Engineering and Biotechnology, the International Centre for Science and High Technology, and UNESCO. Cyril Ponnamperuma, University of Maryland, U.S.A. Julian Chela-Flores, ICTP, Italy, and IDEA, Venezuela. xi FOREWORD As this volume was going to press we learnt of the untimely death of Cyril Ponnamperuma who died of cardiac arrest on December 20, 1994.

This NATO AS was the third in the series of Advanced Study Institutes on neutron stars, which started with 'Timing Neutron Stars', held in Qe me near izmir, Turkey (April 1988), followed by 'Neutron Stars, an Interdis ciplinary Subject', held in Agia Pelagia on the island of Crete (September 1990). The first school centered on our main observational access to neu tron stars, i. e. the timing of radio pulsars and accretion powered neutron stars, and on what timing of neutron stars teaches us of their structure and environment. The second school had as its theme the interplay between diverse areas of physics which find interesting, even exotic applications in the extreme conditions of neutron stars and their magnetospheres. As the field has developed, with the number of observed neutron stars rapidly in creasing, and our knowledge of many individual neutron stars getting deeper and more detailed, an evolutionary picture of neutron stars has started to emerge. This led us to choose 'The Lives of the Neutron Stars' as the uni fying theme of this third Advanced Study Institute on neutron stars. Different types of neutron star activity have been proposed to follow one another in stages during the lives of neutron stars in the same basic population; the evolutionary connection between low-mass X-ray binaries and millisecond radio pulsars is perhaps the prime example."

Collision-or interaction-induced spectroscopy refers to radiative transitions, which are forbidden in free atoms or molecules, but which occur in clusters of interacting atoms or molecules. The most common phenomena are induced absorption, in the infrared region, and induced light scattering, which involves inelastic scattering of visible laser light. The particle interactions giving rise to the necessary induced dipole moments and polarizabilities are modelled at long range by multipole expansions; at short range, electron overlap and exchange mechanisms come into play. Information on atomic and molecular interactions and dynamics in dense media on a picosecond timescale may be drawn from the spectra. Collision-induced absorption in the infrared was discovered at the University of Toronto in 1949 by Crawford, Welsh and Locke who studied liquid O and N. Through the 1950s and 1960s, 2 2 experimental elucidation of the phenomenon, particularly in gases, continued and theoretical underpinnings were established. In the late 1960s, the related phenomenon of collision-induced light scattering was first observed in compressed inert gases. In 1978, an 'Enrico Fermi' Summer School was held at Varenna, Italy, under the directorship of J. Van Kranendonk. The lectures, there, reviewed activity from the previous two decades, during which the approach to the subject had not changed greatly. In 1983, a highly successful NATO Advanced Research Workshop was held at Bonas, France, under the directorship of G. Birnbaum. An important outcome of that meeting was the demonstration of the maturity and sophistication of current experimental and theoretical techniques.

Massive stars occupy an exceptional place in general astrophysics. They trigger many if not all of the important processes in galactic evolution whereas due to their intrinsic brightness, they offer the (only until now) possibility to study the stellar content and stellar behaviour in distant galaxies. The last, say, 25 years, massive stars have been the subject of numerous meetings discussing the influence of massive stars on population synthesis, the number distribution of different types of massive stars, the LBV phenomenon, WR stars, X-ray binaries, stellar winds in massive stars, chemical pecularities in massive stars, supernova explosions of massive stars and the important SN1987A event, the influence of massive stars and chemical evolution of galaxies. It is clear that without a theory of stellar evolution, the study of these topics loses a lot of its significance. Massive star evolution therefore got a chance in these meetings, but rarely as a prime subject. The state of the art, the physical processes and the uncertainties in stellar evolution were barely touched. Even more, the influence of close binaries in all these massive star meetings slowly disappeared the last, say, 13 years without any scientific justification, although a significant fraction of stars occurs in close binaries with periods small enough so that both components will interact during their evolution. Denying the binaries or not discussing their influence on results and conclusions, makes the latter very uncertain or even completely unreliable.

It is with great joy that we present a collection of essays written in honour of Jayant Vishnu Narlikar, who completed 60 years of age on July 19, 1998, by his friends and colleagues, including several of his for mer students. Jayant has had a long research career in astrophysics and cosmology, which he began at Cambridge in 1960, as a student of Sir Fred Hoyle. He started his work with a big bang, expounding on the steady state theory of the Universe and creating a new theory of gravity inspired by Mach's principle. He also worked on action-at-a-distance electrodynamics, inspired by the explorations of Wheeler, Feynman and Hogarth in that direction. This body of work established Jayant's rep utation as a bold and imaginative physicist who was ever willing to take a fresh look at fundamental issues, undeterred by conventional wis dom. This trait, undoubtedly inherited from his teacher and mentor, has always remained with Jayant. It is now most evident in his untir ing efforts to understand anomalies in quasar astronomy, and to develop the quasi-steady state cosmology, along with a group of highly distin guished astronomers including Halton Arp, Geoffrey Burbidge and Fred Hoyle. In spite of all this iconoclastic activity, Jayant remains a part of the mainstream; he appreciates as well as encourages good work along conventional lines by his students and colleagues. This is clear from the range of essays included in this volume, and the variety and distribution of the essayists.

The NATO ARW on the problems of ground-based observations of Solar Eclipses was held in Sinaia (Romania) between 1 and 5 June 1996. The Workshop was divided into seven sessions, in which 17 papers were given, by key speakers, along with 30 oral presentations. Additionally, 30 posters were presented. This issue contains only the invited and oral papers. The posters are to be published in a special issue of the Romanian Astronomical Journal. The contributions were based on our present knowledge of solar corona physics and on the perspectives for future total eclipse observations, focussing especially on that of August 11, 1999, which will be the last eclipse of the century. The workshop sessions reviewed the results of past eclipse observations, coronal hot and cold structures, coronal heating, public education, and instrumental problems. At the end of the meeting a fruitful general discussion drew out problems to be studied and techniques to be used for forthcoming observations. Posters completed the workshop contributions.

It is now a well established tradition that every four years, at the end of winter, a group of "celestial mechanicians" from all over the world gather at the "Alpen gasthof Peter Rosegger" in the Styrian Alps (Ramsau, Austria). This time the colloquium was held from March 17 to March 23, 1996 and was devoted to the Dynamical Behaviour of our Planetary System. The papers covered a large range of questions of current interest: theoretical questions (re- nances, universal properties, non integrability, transport, ... ) and questions about numerical tools ( symplectic maps, indicators of chaos, ... ) were particularly well represented; the never ending problem of the sculpting of the asteroid belt was also qui te popular. You will find in the following pages a pot-pourri of what we listen to; you will miss of course the diversity of accents with which the tunes were delivered: from China, from Japan, from Brazil, from the United-States of America and from all over Europe, East and West. Let us not forget that the comet 199682 (Hyakutake) came to visit us; many an evening was spent on the deck of the Alpengasthof contemplating this celestial visitor who liked to play hide-and-seek behind the spruce trees.

This book reports the Proceedings of the NATO Advanced Research Workshop on "An gular Momentum Evolution of Young Stars" held from 17 to 21 September 1990 at Noto, Italy. The workshop had its immediate origin in a discussion about the availability of stel lar rotation data, that took place in 1987 at Viana do Castelo Portugal during the NATO meeting, Formation and Evolution of Low Mass Stars. We recognized that nearly 20 years had passed since the last meeting on stellar rotation and that significant progress in the observation of rotation rates in low mass stars had been made. During the last 20 years, new efficient instrumentation (CCD and photon counting de tectors and echelle spectrographs) and new analysis techniques (profile Fourier analysis) have allowed us to measure rotational velocities as low as 1-2 km/s and to reach low mass stars in young clusters. Even with these advances, rotational velocities of low mass stars would have remained challenging to determine if all single, low mass stars later than GO had rotational velocities of order or less than 10 km/sec. Evidence that this is not always the case was first provided by the photometric variability data obtained by van Leeuwen and Alphenaar for K dwarfs in the Pleiades and more recently by the vsini measurements of low mass stars in several young clusters."

The Third Microquasar Workshop (or the 'Fifth' Workshop on Galactic Relativ istic Jet Sources), was held in Granada, Andalucia (Spain) on 11-13 September 2000. The aim of this workshop in Granada, following the previous Microquasar Workshops in Greenbelt (1997) and Paris (1998) and the Workshops on galactic sources with relativistic jets in Jodrell Bank (1996) and Milton Keynes (1998), was to focus on the theoretical and observational aspects of microquasars. The study of microquasars, the sources in our Galaxy displaying powerful re lativistic jets, is a rapidly advancing field in astrophysics. The new instrumentation on ground (MERLIN, SCUBA, VLA, VLT) and aboard satellites (ASCA, BSAX, ISO, IXAE and RXTE) has provided important results, and much more is expected to come from Chandra and XMM-Newton. In the further future, powerful instru mentation will come online in the sub-mm (ALMA) and gamma-rays (INTEG RAL), extending our coverage to important regions for the study of microquasars. Energy transport via relativistic jets is one of the most important physical mechan isms taking place in compact objects. Large efforts have been devoted to properly understand the disk-jet connection, and even the effects of rotation or magnetic fields. Several new important advances have been made recently, both from the point of view of the theoretical treatment of jets and the different new observational tests.

Der bekannte Astronom Karl Schwarzschild (1873-1916) gilt als der Begrunder der Astrophysik und als hervorragender Forscher mit einer erstaunlichen Bandbreite seiner Interessen. Arbeiten zur Himmelsmechanik, Elektrodynamik und Relativitatstheorie weisen ihn als vorzuglichen Mathematiker und Physiker auf der Hohe seiner Zeit aus. Untersuchungen zur Photographischen Photometrie, Optik und Spektroskopie zeigen den versierten Beobachter, der sein Messinstrumentarium beherrscht, und schliesslich arbeitete Schwarzschild als Astrophysiker an Sternatmospharen, Kometen, Struktur und Dynamik von Sternsystemen. Die in seinem kurzen Leben entstandene Fulle an wissenschaftlichen Arbeiten ist in drei Banden der Gesamtausgabe gesammelt, erganzt durch biographisches Material, Annotationen von Fachleuten und einen Essay des Nobelpreistragers S. Chandrasekhar."

The twentieth century witnessed some remarkable discoveries: the 1917 publication of Einstein's general theory of relativity, Carnegie astronomer Edwin Hubble's 1929 discovery of the expansion of the universe, evidence for the existence of dark matter, and the discovery of a mysterious dark energy, which is causing the universe to speed up its expansion. This comprehensive volume reviews the theory and measurement of various parameters related to the evolution of the universe. Topics include inflation, string theory, the history of cosmology in the context of measurements being made of the Hubble constant, the matter density, and dark energy, including observational results from the Sloan, Digital Sky Survey, Keck, Magellan, cosmic microwave background experiments, Hubble space telescope and Chandra. With chapters by leading authorities in the field, this book is a valuable resource for graduate students and professional research astronomers.

This authoritative volume was the first to present a comprehensive review of our new understanding of accretion disks around black holes. Interest in black hole accretion disks has undergone a renaissance in recent years because of developments in three complementary areas: theoretical modelling of relativistic plasmas, numerical simulations with supercomputers, and observational tests now possible using new observatories such as the Japanese X-ray satellite, ASCAR. This volume presents review papers on all these topics from leading world authorities who gathered at an international conference in Reykjavik, Iceland. The authors are M. Abramowicz, P. Artymowicz, A. Brandenburg, G. Bjornsson, P. Charles, A. Fabian, J. Krolik, J. -P. Lasota, G. Madejski, R. Narayan, I. Novikov, J. Papaloizou, J. Poutanen, J. Pringle, M. Rees, E. Spiegel, R. Svensson, P. Witta. This 1998 volume provides a far-reaching review of the theory of black hole accretion disks for graduate students and researchers in astrophysics and theoretical physics.