Abstract Details
| Name: Armando Arellano Ferro Affiliation: Institute of Astronomy, UNAM, Mexico Conference ID: ASI2015_395 Title : CCD time-series photometry of Variable Stars in Globular Clusters and the metallicity dependence of Horizontal Branch structure Authors and Co-Authors : Sinetra Giridhar, IIA, Bangalore, India Daniel M. Bramich, Qatar Environment and Energy Research Institute, Qatar Foundation, Tornado Tower, Floor 19, P.O. Box 5825, Doha, Qatar Abstract Type : Oral Abstract Category : Stars, The Milky Way Galaxy and its neighbours Abstract : We present here the major findings of our ongoing program on time-series CCD photometry of globular clusters (GC) based upon the use of the Difference Image Approach (DIA) leading to extraction of very accurate light curves even in the crowded central regions down to V ~ 19 mag with uncertainties of ~0.1 mag. We have discovered nearly 200 variable stars from the extensive photometry of 12 GCs covering a metallcity range of [Fe/H]= -2.1 to -0.5 and have, thereby, updated the census of variables in each system and in some favourable cases have argued for the completenes of the RR Lyrae stars present in the cluster. The absolute magnitude and [Fe/H] for individual RR Lyrae stars has been obtained via the Fourier decomposition of the light curve, after setting the zero points of the calibrations to a homogeneous scale in a sample of 17 GC of Oosterhoff types I and II and including the two metal-rich and peculiar NGC 6388 and NGC 6441, probably of Oo III. This enables us to get an estimate of the mean distance and metallicity of the parent GC and to discuss the dependence of the horizontal branch with the metallicity via the Mv-[Fe/H] relation. We also present a calibration of the P-L relation for SX Phe stars, which enables an independent estimation of the cluster distance. |