CCD time-series photometry of variable stars in globular clusters and the metallicity dependence of the horizontal branch luminosity

Abstract

We describe and summarize the findings from our CCD time-seri es photom- etry of globular clusters (GCs) program and the use of differe nce image analysis (DIA) in the extraction of precise light curves down to V ≈ 19 mag in crowded regions. We have discovered approximately 250 variable sta rs in a sample of 23 selected GCs. The absolute magnitude and [Fe/H] for each ind ividual RR Lyrae is obtained via the Fourier decomposition of the light curve . An average of these parameters leads to the distance and metallicity of the host GCs. We present the mean [Fe/H], M V and distance for 26 GCs based exclusively on the RR Lyrae ligh t curve Fourier decomposition technique on an unprecedented homogeneous scale. We also discuss the luminosity dependence of the horizontal branch (HB) via the M V -[Fe/H] relation. We find that this relation should be consid ered separately for the RRab and RRc stars.