Stellar populations of the globular cluster NGC 5053 investigated using AstroSat-Ultra Violet Imaging Telescope

Abstract

ABSTRACT Globular clusters (GCs), being old and densely packed, serve as ideal laboratories to test stellar evolution theories. Although there is enormous literature on GCs in optical bands, studies in the ultraviolet (UV) regime are sparse. In this work, we study the stellar populations of a metal-poor and a rather dispersed GC, NGC 5053, using the UV instrument of AstroSat, namely the Ultra Violet Imaging Telescope in three far-UV (F154W, F169M, F172M) and three near-UV (N219M, N245M, N263M) filters. Photometry was carried out on these images to construct a catalogue of UV stars, of which the cluster members were identified using Gaia EDR3 catalogue. UV and optical colour–magnitude diagrams (CMDs) help us locate known stellar populations such as blue horizontal branch stars, RR-Lyrae stars, red horizontal branch stars, blue straggler stars (BSSs), SX-Phe, red giant branch, and AGB stars. Based on their locations in the CMDs, we have identified eight new BSS candidates, six probable eBSSs, and an extreme horizontal branch candidate. Their nature has been confirmed by fitting their spectral energy distributions (SEDs) with stellar atmospheric models. We believe the BSS population of this cluster is likely to have a collisional origin based on our analyses of their radial distribution and SEDs. BaSTI-IAC isochrones were generated to characterize the cluster properties, and we find that the observed brightness and colours of cluster members are best fit with a model that is α-enhanced with Y =0.247, [Fe/H] = −1.9, and age =12.5 ± 2.0 Gyr.