Disk Material Inflates Gaia RUWE Values in Single Stars

TL;DR

This study reveals that disk material can inflate Gaia RUWE values in young stars, suggesting the need for a higher threshold to distinguish single stars from binaries in systems with circumstellar disks.

Contribution

It demonstrates that protoplanetary disks can cause inflated RUWE values, leading to a revised threshold for binary detection in young star systems.

Findings

Disk presence inflates RUWE in young stars.

A new RUWE threshold of 2.5 is recommended for disk-hosting stars.

Traditional RUWE > 1.2 may misclassify single stars as binaries.

Abstract

An understanding of the dynamical evolution of binary star systems, and their effects on stellar and planetary evolution, requires well-characterized binary populations across stellar ages. However, the observational resources required to find and characterize binaries are expensive. With the release of high-precision Gaia astrometry, the re-normalized unit weight error (RUWE) statistic has been shown to reveal the presence of binary systems, with RUWE values greater than 1.2 indicating the presence of a stellar companion within $ \sim 1$". Our goal is to assess whether this new diagnostic, which was developed for field-age systems ($>$1 Gyr), applies to young systems; specifically, those that host circumstellar disks. With a control sample of single-star systems, compiled from high-contrast imagining surveys of the Taurus and Upper Scorpius star-forming regions, we compare the RUWE values for systems with and without circumstellar disks. We show that the presence of a protoplanetary disk alone can result in inflated RUWE values. Based on the distribution of the RUWE for disk-bearing single stars, we suggest a more conservative single-star -- binary threshold is warranted in the presence of disk material. We place this cutoff at the distribution's 95th percentile, with RUWE $= 2.5$.