2021MNRAS.502..313K

We present detailed photometric observations of the Galactic globular cluster NGC 7492 using the data obtained with two far-ultraviolet (FUV; 1300-1800 Å) and three near-ultraviolet (NUV; 2000-3000 Å) filters of Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. We confirmed the cluster membership of the extracted sources using Gaia data release 2 (Gaia DR2) proper motion data. We have used colour-magnitude diagrams (CMDs) using UVIT and GAIA filters to separate out different evolutionary stages of the stars present in the cluster. We have identified a new extreme horizontal branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The estimated distance modulus of the cluster is 16.95 ± 0.05 obtained by fitting BaSTI isochrones with cluster parameters, [Fe/H] = -1.8 dex and age =12.0 Gyr on the V - I versus V CMD. Interestingly, only the EHB star and blue horizontal branch stars (BHBs) among the UV-bright hot sources are detected in FUV filters of UVIT. We have derived the effective temperature of BHBs using colour-temperature relation and spectral energy distributions (SEDs) of multiband filters, which are in the range from 8000 to 10 500 K. We find a variation of He abundance of BHBs by fitting the BaSTI ZAHB (zero-age horizontal branch). The range in the He abundance of the BHBs corresponding to the best-fitting isochrones is from 0.247 to 0.350. We have estimated various physical parameters of the newly identified EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have studied the radial distribution of all the sources of the cluster detected in UVIT. The sources detected in FUV filters extend beyond the half-light radius (1.15 arcmin) of the cluster, whereas the sources detected in NUV filters extend beyond the tidal radius (9.2 arcmin) of the cluster.