UVIT/AstroSat Investigation of a low luminous Blue Straggler Star in NGC 362: Detection of extremely low mass white dwarf as companion

TL;DR

This study identifies an extremely low-mass white dwarf as a binary companion to a low luminous blue straggler star in NGC 362, using multi-source data to analyze their properties and formation mechanism.

Contribution

First detection of an extremely low-mass white dwarf companion to a blue straggler in NGC 362, with detailed characterization and formation scenario analysis.

Findings

White dwarf has T_eff=15000 K, radius=0.17 Rsun, luminosity=1.40 Lsun, mass=0.19-0.20 Msun

Blue straggler's position suggests formation via Case A/B mass transfer

Confirmed binary nature through spectral energy distribution analysis

Abstract

In the present study, we identified an extremely low-mass white dwarf as a companion to a low luminous blue straggler star within the Galactic globular cluster NGC 362. To conduct the analysis, we utilized data obtained from various sources, including AstroSat Ultra Violet Imaging Telescope, UVOT, and the 2.2-m ESO telescope. By examining the spectral energy distribution of the blue straggler star candidate, we successfully identified an extremely low mass white dwarf as its binary companion. We determined the effective temperature, radius, and luminosity for both, the extremely low-mass white dwarf and the blue straggler star candidate. Specifically, the extremely low-mass white dwarf exhibits an effective temperature of 15000 K, a radius of 0.17 Rsun, a luminosity of 1.40 Lsun, and a mass range of 0.19-0.20 Msun. Furthermore, the position of the straggler star within the cluster suggests their formation via the Case A/B mass-transfer mechanism in a low-density environment.