UOCS – XI. Study of blue straggler stars in open cluster NGC 7142 using UVIT/AstroSat

Abstract

We present a study of blue straggler stars (BSSs) of open cluster NGC 7142 using AstroSat/UVIT data and other archival data. Using a machine-learning-based algorithm, ML-MOC, on Gaia DR3 data, we find 546 sources as cluster members. Based on the location on the Gaia colour–magnitude diagram, we identify 10 BSS candidates, also detected in UVIT/F148W filter. We study the variable nature of BSSs by constructing their light curves using the Transiting Exoplanet Survey Satellite data. Two BSSs reported as eclipsing binaries in Gaia DR3 are confirmed to be eclipsing binaries based on our analysis and also show the presence of hot companions as per the multiwavelength spectral energy distributions (SEDs). The physical parameters of the hot companions of these two BSSs derived by fitting binary models to their light curves and those derived from the SEDs are found to be in good agreement. Additionally, five more BSSs in the cluster shows UV excess, four of which are likely to have a hot companion based on SEDs. The hot companions with the estimated temperatures ∼14 000–28 000 K, radii ∼0.01–0.05 R, and luminosities ∼0.03–0.1 L are inferred to be extremely low-mass (0.6 M) white dwarfs (WDs). For the first time in an open cluster, we find the entire range of masses in WDs found as hot companions of BSSs. These masses imply that the Case-A/Case-B mass transfer and merger are responsible for the formation of at least 60 per cent of the BSSs of this cluster.