Pulsating Stars in Globular Clusters and Their Use

Summary

About Pulsating Stars

Introduction

The discussions in the following sections are limited to pulsating variables and thus omit such objects as eclipsing and cataclysmic variables. Rather than try to cover every conceivable aspect of the subject an attempt is made to discuss in detail a few problems of current interest. This has meant that some types of pulsating variable are not dealt with at all, e.g. Type II Cepheids (including RV Tau stars), SX Phe variables and the recently discovered pulsating K giants in globular clusters (Edmonds and Gilliland 1996). In several of the areas covered strongly divergent views are held by different workers. In such cases an attempt is made to summarize the arguments of the various groups whilst at the same time indicating what in the present writer's opinion seems most likely to be the correct interpretation.

Pulsating stars are of importance for a variety of reasons. First, a study of their light, colour, and radial velocity, changes through the pulsation cycle tell us a great deal about the stars themselves – about their structure – which we cannot easily learn in other ways. Secondly, because pulsating variables are rather easily classified into groups with homogeneous properties it is possible to use them, provided their absolute magnitudes can be calibrated, to derive distances. Pulsating stars are at the basis of the galactic and extragalactic distance scales and are important in determining the distances and ages of classical, old, globular clusters.