This volume contains papers presented at IAU Colloquium No. 90. at the Crimean Astrophysical Observatory in May of 1985. A few additional contributions are included from authors who for various reasons were unable to attend the meeting. Four years have passed since the last major international conference on chemically peculiar stars of the upper main sequence was held in Liege. Belgium in 1981. Previous conferences were held in 1975 (Vienna. Austria) and in 1965 (Greenbelt. Maryland. USA). As the proceedings of this Colloquium show. the recent availability of ultraviolet spectra of large numbers of normal and chemically peculiar A and B stars is having a major impact on the way we study these objects. and has led to many new. exciting and unanticipated results. Simultaneously. the more traditional study of optical spectra has been advanced through the increasing use of very high spectral resolution with high signal-to-noise detectors. The chemically peculiar (CP) stars on the upper main sequence belong in the standard framework within which we understand stellar evolution and the history of matter. Recent work has made it clear that the unusual chemistry and magnetic structure of these objects is of relevance across the broad domain of stellar astronomy. from the upper main sequence to horizontal branch stars and white dwarfs. Metal poor (J>. Boo) as well as metal rich (Ap. Am) stars are an integral part of the picture.

From the reviews: Astronomy and Astrophysics Abstracts has appeared in semi-annual volumes since 1969 and it has already become one of the fundamental publications in the fields of astronomy, astrophysics and neighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. ... The abstracts are classified under more than hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world." Space Science Reviews #1 "Dividing the whole field plus related subjects into 108 categories, each work is numbered and most are accompanied by brief abstracts. Fairly comprehensive cross-referencing links relevant papers to more than one category, and exhaustive author and subject indices are to be found at the back, making the catalogues easy to use. The series appears to be so complete in its coverage and always less than a year out of date that I shall certainly have to make a little more space on those shelves for future volumes." The Observatory Magazine #1

Throughout his career Sir Robert Wilson has demonstrated that advances in a wide variety of fields in astrophysics and laboratory physics are achievable through the application of fundamental plasma spectroscopy. His work has included: optical studies that probed the nature of interstellar dust and first revealed the existence of O star winds; vacuum ultraviolet and X-ray diagnosis of fusion plasmas; rocket ultraviolet and X-ray observations of the Sun; and the conception, development and use of the International Ultraviolet Explorer (IUE) satellite which has contributed greatly to stellar, interstellar and extragalactic astrophysics. This volume contains reviews honouring Sir Robert and reflecting his interests.

The first comprehensive monograph on this active and productive field of research investigates solar-type activity amongst the large spectrum of low- and middle-mass main sequence stars, and presents the subject in a systematic and comprehensive fashion.

Despite more than one century of observational stellar spectroscopy, the resulting data are not available in an easily accessible format. The necessity of such basic information is greater than ever, because new wavelength regions (ultraviolet, infrared) are now accessible and because modern receivers can only analyze short stretches of spectra, so that a careful pre-selection of strategic elements is mandatory. This book presents a summary of our knowledge of the behavior of all chemical elements identified in stars, based on observations rather than on their interpretations. Whenever possible the behavior is described quantitatively, with the help of equivalent widths in different types of stars, or different ionization stages, for both absorption and emission features. It will be essential to the spectroscopist when confronted with questions like the following: . What is the behavior of europium in metallic line stars or in S-type stars? Are the neutral lines of this element visible, are they strengthened or weakened with regard to normal dwarfs? A huge amount of data has been gathered by experts in the field and presented in a way that will be invaluable to professional astrophysicists, cosmochemists and their students.

The authors give an overview of atomic diffusion as applied to all types of stars, showing where it plays an essential role and how it can be implemented in modelling. Part I describes the tools that are required to include atomic diffusion in models of stellar interiors and atmospheres. An important role is played by the gradient of partial radiative pressure, or radiative acceleration, which is usually neglected in stellar evolution. In Part II, the authors systematically review the contribution of atomic diffusion to each evolutionary step. The dominant effects of atomic diffusion are accompanied by more subtle effects on a large number of structural properties throughout evolution. The goal of this book is to provide the means for the astrophysicist or graduate student to evaluate the importance of atomic diffusion in a given star. A fundamental physical process, atomic diffusion can significantly affect the superficial abundances of stars and/or their evolution. This guide includes all the information needed to take proper account of atomic diffusion's impact.

"Astronomy and Astrophysics Abstracts" appearing twice a year has become oneof the fundamental publications in the fields of astronomy, astrophysics andneighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. The abstrats are classified under more than a hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world.