On behalf of the IAU Commission 48 "High Energy Astrophysics" a special session on "CNO Isotopes in Astrophysics" was held at the General Assembly of IAU in Grenoble on August 30, 1976. This topic was chosen since it has recently included many exciting developments in various domains of physics and astrophysics such as for instance meteoritical studies, radioastronomy measurements of the interstellar gas, new determinations of nuclear reactions cross-sections and fractionation processes. The papers of this volume are the written versions of the talks which were presented during this session and cover the most recent observations and theoretical developments re garding this fast-growing field. Let me thank first Professor Martin Rees (Institute of Astronomy at Cambridge) the chairman of IAU Commission 48, who has sponsored this special session and made it possible. I am indebted to the authors of the papers for their contributions and all the work they have put in the excellent presentation of the material. lowe special thanks to Professor William A. Fowler (Kellogg Laboratory at Cal tech) who has superbly chaired this session and made it very exciting and lively, to Professor Beatrice M. Tinsley (Yale University) who accep ted the difficult task to conclude and sGmmarize on such a burning and moving topic, and to Dr James Lequeux for his invaluable help in the edition of several contributions. Finally, the edition of this book would not have been possible with out the skilled and generous aid of Miss Jeannette Caro.

The 4th European Regional Meeting in Astronomy, entitled "Stars and Star Systems", was held in Uppsala, Sweden, on August 7 -12, 1978. It was attended by 228 participants from 24 countries. Over 100 papers were presented; this required parallel sessions throughout the Meeting. Financial support was given by the IAU, the Swedish Department of Education, the Swedish Natural Science Research Council, the Swedish Institute and the University of Uppsala. The members of the Scientific and Local Organizing Committees are listed below, and I thank all of them for their contributions to the Meeting. The Meeting was divided into six sections, according to the scien tific topics: Galaxies (A) - including galactic structure and star for mation; High-Energy Astrophysics (B); Stars (C); Interstellar Processes (D); Astronomical Instrumentation (E) and Education in Astronomy (F). In each section a number of Invited Papers were presented as well as a large number of contributed papers. In addition, each day a General Lecture was given by an Invited Speaker. The present volume contains all the General Lectures and all the Invited Papers presented during the Meeting. In three cases, however, and for various reasons, only brief summaries have been available. Abstracts of the contributed papers may be found in Uppsala Astronomical Observatory, Report No. 12.

The IAU Colloquium No.49, on the formation of images from spatial coherence functions in astronomy, was held at Groningen, the Netherlands, during the period 10-12 August 1978. The colloquium was attended by 108 participants from 14 countries (U.S.A. 29, the Netherlands 20, U.K. 19, Germany 10, France 7, Australia 5, Canada 5, Japan 4, India 2, New Zea land 2, Sweden 2, Argentina I, Belgium I, Israel I). It was sponsored by the Netherlands Foundation for Radio Astronomy, the International Astronomical Union, the Department of Education and Sciences, the Union Radio-Scientifique Internationale, the Leiden Kerkhoven-Bosscha Foundat ion and the State University at Groningen. This volume contains 36 of the 37 papers presented. Nearly all papers are followed by a sununary of the discussion that took place after their presentation. A few papers, published in full elsewhere, are given only as abstracts. The majority of the papers are related to aperture synthesis in radio astronomy; a small number deal with optical astronomy and with applications in acoustics and medicine. The presentations are divided in 7 groups: aperture synthesis and its deficiencies, the problem of limited or missing phase information, techniques for processing and data display, optical interferometric methods, maximum entropy image reconstruction, other image improvement methods, and a survey of image formation from projections. Each group contains one or two invited lectures (see Table of Contents), intended as surveys of particular areas; on the average they occupy twice as many pages as the other papers.

Proceedings of a Symposium organized within the XIXth URSI General Assembly held in Helsinki, Finland, July 31-August 8, 1978

The last major conference on infrared astronomy was the IAU Symposium No. 96 in June 1980. Since then, the discipline has continued to mature and to contribute to all branches of astrophysics. One particular area of growth has been in spectroscopic capabilities at all infrared wavelengths. The purpose of the Symposium in Toledo was to review the scientific questions to be addressed via infrared spectroscopy and to provide, in the proceedings, a useful summary of the field. The sensitivity of infrared spectroscopic observations is still generally limited by detector characteristics or by thermal background radiation. However in recent years improvements in detector technology together with developments in spectroscopic instrumentation have made possible both quite detailed spectroscopy of the brighter members of many classes of galactic sources and also begun to open up some infrared spectroscopy of extragalactic sources. The potential of the field in the next decade or two is clear. The lRAS mission has completed one of the pre-requisites, namely an all-sky photometric survey. Major space missions utilising cryogenic infrared telescopes have been approved in Europe (ISO) and seem likely in the USA (SIRTF); plans for space submillimeter telescopes are firming up. On the ground large telescopes optimized for infrared observations are now in operation at high altitude sites and specialized submillimeter facilities are under construction. The particular advantages of planned, very large telescopes for infrared observations are widely accepted.

Interstellar matter is one of the most active fields of research in present-day astronomy. Observational information spans the full electromagnetic spectrum from gamma rays through rocket-ultraviolet, optical, infrared and millimeter to long radio waves. Results of research in physical chemistry find as much application as mathematical methods. Interstellar matter plays a leading role in studies of our Galaxy and of external galaxies, and contributes increasingly to stellar astronomy. At the 16th General Assembly of the International Astronomical Union, held in August 1976 in Grenoble, France, the many new developments in this vast field were surveyed in a number of sessions of Commission 34 (Interstellar Matter), mostly jointly with other Commissions of the Union. Separate sessions were devoted to: The hot interstellar gas phase, Interaction of stars and interstellar medium, Interstellar molecules and dust, The large-scale distribution of interstellar matter in the Galaxy, and Interstellar matter in external galaxies. Twenty-four invited review papers were presented and discussed in these sessions. The quality and success of these topical reviews made it seem desirable to make them available to a wider audience. Professor Edith Muller, the new General Secretary of the IAU, enthusiastically supported the idea. Most importantly, the reviewers - who had originally been pro mised that an oral paper was the only requirement - agreed to prepare written versions. I am grateful to Mrs. Muller, to the authors, and to Reidel Publishing for their collaboration in the preparation of this book.