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

A gap in the double white dwarf separation distribution caused by the common-envelope evolution: astrometric evidence from Gaia

“…Systems with more than 2 companions could contribute to lift up the log 𝛿𝑎 > −1 wing of the distribution. As discussed in Belokurov et al (2020) and Penoyre et al (2022), triples and higher multiples tend to provide objects with the highest detected wobble amplitude 𝛿𝑎. Note that to date, very few observational constraints exist for WDs in triples (see e.g.…”

“…Observational biases and sample contamination. Using the results of Penoyre et al (2021), (see also Penoyre et al 2020Penoyre et al , 2022, we estimate the selection efficiency of the astrometric wobble method not to vary dramatically in the range of 𝛿𝑎 considered here. Note however that as shown in Figure 15 of Penoyre et al (2021) the drop in efficiency around log 𝛿𝑎 ≈ −2 is fast and thus may have affected the lowest amplitude portion of the wobble distribution more than envisaged.…”

Vetting the Lobster Diagram: Searching for Unseen Companions in Wide Binaries using NASA Space Exoplanet Missions

“…To provide additional evidence that the "Lobster diagram" finds unresolved companions, we can examine the Gaia data itself. The Reduced Unit Weight Error (RUWE) parameter is an indicator of how good the astrometric fit is for a given star and can be used as a powerful tool to identify unresolved binaries within Gaia (Belokurov et al 2020;Stassun & Torres 2021;Penoyre et al 2022). Single stars with good astrometric fits typically have a RUWE between 1.0 and 1.4, although Stassun & Torres (2021) found evidence in a sample of eclipsing binaries systems that an eDR3 RUWE value in that range does not guarantee that a star does not have an unresolved companion.…”

HD-TESS: An Asteroseismic Catalog of Bright Red Giants within TESS Continuous Viewing Zones

“…The ever increasing precision of astrometry from the Gaia space mission (Gaia Collaboration et al 2018 has proven extremely valuable for the study of both resolved (e.g., El-Badry et al 2019Makarov & Fabricius 2021) and unresolved stellar companions (e.g., Belokurov et al 2020;Penoyre et al 2022) of nearby stars. Of particular interest are binary systems for which one of its components is an oscillating giant because these enable direct constraints on the age of the co-eval companion.…”