Variable Stars: Key to Stellar Evolution and Structure of the Galaxies

Variable star studies play an important roles in understanding the physical properties of the galaxies and clusters they are present in. The stars in globular clusters are believed to have formed roughly at the same time (although there is also mounting evidence that some clusters have formed via several episodes of star formation), from the same primordial material, and with the same composition. This should lead to a homogeneity in certain fundamental properties of the stars within each cluster, but with differences between the clusters. Knowledge about these properties, such as metallicity, age, and kinematics, are therefore important. One way to obtain better constraints on some of these physical parameters is to study the population of variable stars, especially RR Lyrae stars. Observing variable stars in different galaxy environments makes it possible to relate the types of variable stars to the stellar populations in their host galaxies.