Studies of Blue Stragglers in star clusters with AstroSat

Abstract

We present an overview of Blue Stragglers (BSs) studies in star clusters using UVIT observations onboard AstroSat. The formation of BSs has puzzled scientists for several decades since their discovery. Two main scenarios proposed for their formation are stellar collisions leading to mergers in high-density environments and mass transfer between an evolved primary donor to the secondary star, mostly dominating in low-density environments. These stars being bluer and brighter than the main-sequence (MS) turn-off stars in the optical color-magnitude diagrams should have evolved long ago given their respective cluster ages according to the standard stellar evolution theory. BSs, being massive and hotter than the dominant cluster population of MS and red-giant stars mainly emit in UV. Thus, UV observations are advantageous in identifying these stars by reducing the crowding. Most of the studies related to the BSs are based on the NUV and optical data from HST, Gaia, and ground-based observations. However, dedicated FUV surveys of star clusters are needed to identify the hot companions to BSs and understand their nature. Taking the advantage of multiple filters in the two UV channels of UVIT, we have combined them with the multi-wavelength archival data to sample the spectral energy distributions of BSs and unravel their properties. We discuss the exciting results from the UV analysis of BSs in open and globular clusters.