Young Blue Straggler Stars in the Galactic Field

TL;DR

This paper identifies 80 field blue straggler stars with UV excess indicating hot white dwarf companions, analyzes their properties, and suggests a formation mechanism involving case B mass transfer.

Contribution

It introduces a new fitting routine for binary SEDs and provides evidence supporting the case B mass transfer as the primary formation channel for field blue stragglers.

Findings

80 stars with UV excess identified

White dwarf companions peak at ~0.4 solar masses

Lower limit of mass transfer efficiency estimated at ~0.5

Abstract

In this study we present an analysis of a sample of field blue straggler (BS) stars that show high ultra violet emission in their spectral energy distributions (SED): indication of a hot white dwarf (WD) companion to BS. Using photometry available in the Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX ) surveys we identified 80 stars with UV excess. To determine the parameter distributions (mass, temperature and age) of the WD companions, we developed a fitting routine that could fit binary model SEDs to the observed SED. Results from this fit indicate the need for a hot WD companion to provide the excess UV flux. The WD mass distribution peaks at $\sim$$0.4\ M_{\odot}$, suggesting the primary formation channel of field BSs is case B mass transfer, i.e. when the donor star is in red giant phase of its evolution. Based on stellar evolutionary models, we estimate the lower limit of the binary mass transfer efficiency to be $\beta \sim 0.5$.