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

TL;DR

This study uses AstroSat's UV imaging to analyze the stellar populations of globular cluster NGC 5053, identifying various stellar types and new candidates, and inferring their origins and cluster properties.

Contribution

First UV-based detailed stellar population analysis of NGC 5053, identifying new stellar candidates and characterizing cluster properties with spectral and photometric data.

Findings

Identified 8 new BSS candidates and 6 probable eBSSs.

Cluster's BSS population likely formed through stellar collisions.

Cluster properties best fit with alpha-enhanced models, age 10.5-14.5 Gyr.

Abstract

Globular clusters being old and densely packed serve as ideal laboratories to test stellar evolution theories. Although there is enormous literature on globular clusters 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 globular cluster, 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 CMDs help us locate known stellar populations such as BHB stars, RR-Lyrae stars, RHB stars, BSSs, SX-Phe, RGB and AGB stars. Based on their locations in the CMDs, we have identified 8 new BSS candidates, 6 probable eBSSs, and an EHB candidate. Their nature has been confirmed by fitting their spectral energy distributions 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 alpha-enhanced with a helium fraction of 0.247, metallicity of -1.9 dex and age within a range of 10.5-14.5 Gyr.