Stellar population in GC NGC 5053

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.