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 enormous amounts of energy radiated from the active nuclei of galaxies vary on short time scales, and the emission regions are difficult to observe. To provide a complete understanding of these phenomena a wide variety of studies is presented in this volume. The contributions are broadly divided between line and continuum variability, with observational results, methodological approaches, and theoretical models accompanying each. The final part is devoted to the important aspect of propagation-induced variability.

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 physical processes driving the different manifestations of the phe nomenon of active galactic nuclei have been studied extensively during the last decade. A major obstacle in all attempts to understand the relevant pro cesses has always been the wide range of frequencies over which significant fractions of the total power are emitted. During the last decade, orbiting telescopes and instrumental improvements for ground-based instrumenta tion provided the means for major advancements on the observational side. The organizers felt that it was timely to organize a meeting to discuss the impact of this new situation on the understanding of the relevant physical processes. More then 400 astrophysicists were interested in participating in the meeting, in spite of the constraints on overseas travel which were imposed in early 1991. Unfortunately only 220 participants could be hosted by the Max-Planck-Haus, the site of the 1991 Heidelberg conference. The meet ing was organized by Sonderforschungsbereich 328 "Evolution of Galaxies". During 5 sessions, most of which lasted for one day each, 47 invited and con tributed talks and 150 poster papers were given, most, but not all, of which are included in these proceedings. With a few exceptions the order of the written texts follows that of the oral contributions during the meeting. The arrangement of posters into the five sections was not always unambiguous. We hope to have placed them in the most appropriate sections, in which they are listed in alphabetical order.

With the advent of space observatories and modern developments in ground based astronomy and concurrent progress in the theoretical understanding of these observations it has become clear that accretion of material on to compact objects is an ubiquitous mechanism powering very diverse astrophysical sources ranging in size and luminosity by many orders of magnitude. A problem common to these systems is that the material accreted must in general get rid of its angular momentum and this leads to the formation of an Accretion Disk which allows angular momentum re-distribution and converts potential energy into radiation with an efficiency which can be higher than the nuclear burning yield. These systems range in size from quasars and active galactic nuclei to accretion disks around forming stars and the early solar system and to compact binaries such as cataclysmic variables and low-mass X-ray binaries. Other objects that should be mentioned in this context are 88433, the black hole binary candidates, and possibly gamma-ray burst sources. Observations of these systems have provided important constraints for theoretical accretion disk models on widely differing scales, lumi nosities, mass-transfer rates and physical environments."