CCD TIME-SERIES PHOTOMETRY OF VARIABLE STARS IN GLOBULAR CLUSTERS AND THE METALLICITY DEPENDENCE OF THE HORIZONTAL BRANCH LUMINOSITY

We describe and summarize the findings from our CCD time-series photometry of globular clusters (GCs) program and the use of difference image analysis (DIA) in the extraction of precise light curves down to V approximate to 19 mag in crowded regions. We have discovered approximately 250 variable stars in a sample of 23 selected GCs. The absolute magnitude and [Fe/H] for each individual 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 light 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 considered separately for the RRab and RRc stars.