UVIT Observations of UV-Bright stars in Galactic Globular Clusters

Abstract

We analyze four Galactic halo globular clusters (GCs): NGC7492, NGC4590, NGC4147 and NGC5053 using three each far-UV and near-UV filters of Ultraviolet Imaging Telescope (UVIT) onboard Indian satellite AstroSat. The unprecedented resolution (∼ 1.5 arcsec) of UVIT has able to resolve core cluster members of GCs. We present the color-magnitude diagram (CMD) for all these sources. We determine distance, metallicity and age of the GCs using isochrone fitting on CMDs. We have detected total numbers of 215 horizontal branch (HB) stars,∼ 50 Blue stragglers (BSS), 3 white dwarfs and 1 ultra UV bright sources in four GCs. We study the temperature, spectral energy distribution and evolution curve of newly detected UV bright sources using Kurucz stellar atmosphere models with the help of six UVIT fliters and five Pan-STARRS filters (Optical/IR). We confirm the membership of newly detected UV bright sources using GAIA DR2 catalog and study the kinematics of BSS and HB stars using GAIA proper motion measurements. We show the geometrical distribution of UV bright cluster members with surface density plots of UVIT resolved core members and GALEX observed outer sources within one degree field of view. We present the global metallicity relation of Galactic halo GCs using integrated magnitude of our observed four GCs.