Problems Of Stellar Convection

D. O. GOUGH Institute of Astronomy. Madingley Road. Cambridge. U. K. IAU Colloquium 66 on 'Problems of Solar and Stellar Oscillations' was held at the Crimean Astrophysical Observatory, U. S. S. R. , on 1-5 September, 1981. The principal purpose of the colloquium was to study the low-amplitude oscillations of the Sun and, to a lesser extent, to consider similar oscillations of other stars. Much of the emphasis of the discussions was on the diagnostic value of the oscilla tions. In the last few years we have become aware that the frequencies of the five-minute modes of high degree, which constitute the major component of the oscillations discovered twenty years ago by Evans and Michaud, can be used to put quite tight bounds on the stratification of the solar convection zone. These permit a calibration of solar models computed from so-called standard evolution theory. Modes of low degree penetrate beneath the convection zone to the core of the Sun, and can in principle test the evolution theory. Therefore there was considerable interest in the reports of the latest observations of such modes. Broadly speaking, those observations confirm the cali bration by the high-degree modes, but there remain some systematic discrepancies that demand some revision of the theory. Besides the gross aspects of evolution theory, there are also more intricate details to be understood.

This book represents the proceedings of a NATO Advanced Study Institute which was held at Bonas from August 25 till Sep tember 5, 1980 and was devoted to the study of "Solar Phenomena in Stars and Stellar Systems". It is intended for a broad audi ence. Students and post-doctoral scientists for example can dis cover new aspects of astrophysics. The general spirit of the ASI was aimed at presenting a unified aspect of astrophysical phenomena which can be studied intensively on the Sun although they are of a much more general nature. On the other hand, spe cialists in solar or stellar physics will find here the latest theoretical developments and/or the most recent observations made in their own field of research. An extensive bibliography will be found throughout the various sections, to which the reader may refer, for more detailed developments in various specific areas. In the past, stellar and solar astrophysics have more or less followed their own independent tracks. However, with the rapid development of modern techniques, in particular artificial satellites like the International Ultraviolet Explorer and the Einstein Observatory, which provide a new wealth of data, it appears that chromospheres, coronae, magnetic fields, mass loss and stellar winds, etc . . . . , are found not only in the Sun but occur also in other stars. Frequently these other stars represent quite different conditions of gravity, lumino~ity, and other parameters from those occurring in the Sun.

This volume contains the reviews and poster papers presented at the workshop Solar Convection and Oscillations and their Relationship: SCORe '96, held in Arhus, Denmark, May 27 - 31, 1996. The aim of this workshop was to bring together experts in the fields of convection and helioseismology, and to stimulate collaborations and joint research. The participation to this workshop was purposely kept limited in order to provide optimal conditions for informal discussions. In autumn of 199,5 the long-awaited GONG network of solar telescopes became fully operational and the first data already show significant improvement over existing datasets on solar oscillations. Furthermore, in December of 1995 the satellite SOHO was launched which, together with GONG, provides a major step forward in both the quantity and the quality of available solar oscillation data. It is with this in mind that we decided to organize the workshop to prepare for the optimal use of this wealth of data, with which to deepen our understanding of solar structure and specifically, of one of the longest-standing problems in solar and stellar modelling: the treatment of convection.

"Stellar Physics" is a rather unique book in the growing literature on star formation and evolution. Not only does the author, a leading expert in the field, give a very thorough description of the current knowledge about stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 650 entries makes this book an unparalleled source of references. "Stellar Evolution and Stability" is the second volume and can be read, as can the first volume, as a largely independent work. It traces in great detail the evolution of the protostar towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to the mighty supernovae explosions and blackhole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars.