The study of stellar pulsation is an old topic, but still a very active research area. Observations from space are now starting to become available and the field is probably more active than ever. The hope is that these data will help us resolve some notoriously difficult problems in stellar physics concerning convection, rotation, and magnetic fields. In this book, the author takes us to the frontiers of research in this field. The title Challenges in Stellar Pulsation reflects the main message of the book, with the emphasis on unsolved problems in stellar pulsation.
The book begins with a brief theoretical background presented almost without formulae. Still, unprepared readers become suffciently equipped with basic concepts needed for understanding the material presented later. Subsequent sections are devoted to various types of pulsating stars ordered according to evolutionary phases, starting with stars on or near the main sequence and ending with white dwarfs. We find a comprehensive description of the observational characteristics of each type of star, detailed information on selected individual objects of particular interest, and interpretations in terms of stellar physics.
The unsolved problems constitute challenges for both stellar pulsation and stellar evolution. In some cases we do not understand how the modes are excited, and even in the cases where we do, the observed range of pulsation is a puzzle. The most important data for testing stellar models are the oscillation frequencies. In a number of cases, including the Sun and Cepheids, comparisons of observed and calculated frequencies point to a need for improvement in model calculations and/or the stellar microphysics. In recent years, much progress has been made concerning the effects of rotation and magnetic fields on stellar pulsation, but much remains to be done in this important and difficult subject.
There is a wide spectrum of people who may benefit from reading this book. From amateurs, who are often passionate variable star observers and may want to learn about the context of their activity, to professional astronomers who spent their careers on studying pulsating stars but may want to broaden their knowledge and have a handy source of references to the original papers. Most importantly of all, however, I would recommend this book to young astronomers looking for challenging problems in the subject.
Warsaw, February 2010
As a result of a commitment to develop software for the Southern African Large Telescope, I had to break astronomical research for five years. To re-start research after this hiatus, I had to embark on an extensive study of the literature. This was no easy task, but I soon found myself organizing the comprehensive information in terms of chapter topics. It struck me that if these notes were helpful to me, they might be helpful to others, and so the idea behind this book was born.
This book is, in reality, a review of the state of research on pulsating stars over the last ten years, but I have included material which I hope will assist the young researcher who intends writing a PhD or even an undergraduate who is searching for an entry into a research career in this field. There is no in-depth description of stellar pulsation and few equations in this book. Several excellent books already exist which cover this topic. My aim was to provide a clear explanation in physical terms for the processes which occur in pulsating stars. The field of stellar pulsation is large and it is difficult to have a reasonable grasp of the main research results in all the different classes of pulsating stars. My hope is that this book will fill that gap. In particular, I have tried to highlight problems which offer a reasonable prospect for solution, which are the challenges referred to in the title.
At the end of each chapter there is a "Discussion" section. This section is a collection of thoughts which expresses my personal views on the topics. The idea is to provide a recapitulation of what is known and more importantly, what I believe needs to be explored.
A great motivating factor for writing this book is the encouragement I received from my colleagues. Without this support this book would certainly not have been written. I thank Michel Breger, Conny Aerts, Don Kurtz, Mike Jerzykiewicz and Hiromoto Shibahashi for their encouragement. Most of all I thank Wojtek Dziembowski for reading the book and supplying useful comments. I also thank Igor Soszynski for kindly allowing the inclusion of two of his figures and to Joyce Guzik for useful discussions. This book could not have been made without the use of NASA's Astrophysics Data System.
Luis A. Balona
Cape Town, February 2010
List of Contributors
L. A. Balona
South African Astronomical Observatory