Study of blue metal-poor stars using UVIT/AstroSat

TL;DR

This study uses UV imaging from AstroSat to analyze blue metal-poor stars, revealing their binary nature and possible formation mechanisms involving white dwarf companions.

Contribution

First UV imaging observations of blue metal-poor stars with spectral energy distribution fitting to explore their binary nature and formation channels.

Findings

BMP17's companion may be a cooled white dwarf undetectable in UV.

BMP37 has a hot white dwarf companion, indicating mass transfer.

Both stars are confirmed binaries with different companion characteristics.

Abstract

Blue metal-poor stars are main-sequence stars that are bluer and brighter than typical turn-off stars in metal-poor globular clusters. They are thought to have either evolved through post-mass transfer mechanisms as field blue straggler stars or have accreted from Milky Way dwarf satellite galaxies. It has been found that a considerable fraction of blue metal poor stars are binaries, possibly with a compact companion. We observed 27 blue metal poor stars using UV imaging telescope of AstroSat in two far-UV filters, F148W and F169M. In this work, we explain the possible formation channels of two stars, BMP17 and BMP37. We fit BMP17 with a single-component spectral energy distribution whereas BMP37 with a binary-component spectral energy distribution. As both of them are known SB1s, we suggest that the WD companion of BMP17 may have cooled down so that it is out of UV imaging telescope detection limit. On the other hand, we discover a normal mass white dwarf as the hot companion of BMP37, indicating mass transfer as the possible formation channel