Astrometric identification of nearby binary stars II: Astrometric binaries in the Gaia Catalogue of Nearby Stars

TL;DR

This study uses Gaia data to identify unresolved binary stars through astrometric deviations, revealing the binary fraction among different stellar types and discussing the method's limitations for detecting non-luminous companions.

Contribution

The paper introduces a renormalized astrometric deviation metric (LUWE) for binary detection and applies it to Gaia data, providing the first large-scale binary candidate catalog within 100 pc.

Findings

Approximately 10% of sources within 100 pc are binary candidates.

Binary fraction is about 20% for giants, 10% for Main Sequence stars, and less than 1% for White Dwarfs.

VIMs may account for a significant portion of binaries among sub-Solar mass MS stars.

Abstract

We examine the capacity to identify binary systems from astrometric deviations alone. We apply our analysis to the Gaia eDR3 and DR2 data, specifically the Gaia Catalogue of Nearby Stars. We show we must renormalize (R)UWE over the local volume to avoid biasing local observations, giving a Local Unit Weight Error (LUWE). We use the simple criterion of LUWE>2, along with a handful of quality cuts to remove likely contaminants, to identify unresolved binary candidates. We identify 22,699 binary candidates within 100 pc of the Sun (just under 10% of sources in this volume). We find an astrometric binary candidate fraction of around 20% for giant stars, 10% on the Main Sequence and lower than 1% for White Dwarfs. We also look for Variability Induced Movers, by computing the correlation between photometric variability and astrometric noise -- and show that VIMs may dominate the binary population of sub-Solar mass MS stars. We discuss the possibility and limitations of identifying non-luminous massive companions from astrometry alone, but find that our method is insensitive to these. Finally, we compare the astrometric deviations of MS binaries to the simulated sample from paper I, which show excellent agreement, and compute the astrometric candidate binary fraction as a function of absolute magnitude.