Comoving Stars in Gaia DR1: An Abundance of Very Wide Separation Comoving Pairs
Abstract
The primary sample of the Gaia Data Release 1 is the TychoGaia Astrometric Solution (TGAS): ≈2 million Tycho2 sources with improved parallaxes and proper motions relative to the initial catalog. This increased astrometric precision presents an opportunity to find new binary stars and moving groups. We search for highconfidence comoving pairs of stars in TGAS by identifying pairs of stars consistent with having the same 3D velocity using a marginalized likelihood ratio test to discriminate candidate comoving pairs from the field population. Although we perform some visualizations using (biascorrected) inverse parallax as a point estimate of distance, the likelihood ratio is computed with a probabilistic model that includes the covariances of parallax and proper motions and marginalizes the (unknown) true distances and 3D velocities of the stars. We find 13,085 comoving star pairs among 10,606 unique stars with separations as large as 10 pc (our search limit). Some of these pairs form larger groups through mutual comoving neighbors: many of these pair networks correspond to known open clusters and OB associations, but we also report the discovery of several new comoving groups. Most surprisingly, we find a large number of very wide (> 1 pc) separation comoving star pairs, the number of which increases with increasing separation and cannot be explained purely by falsepositive contamination. Our key result is a catalog of highconfidence comoving pairs of stars in TGAS. We discuss the utility of this catalog for making dynamical inferences about the Galaxy, testing stellar atmosphere models, and validating chemical abundance measurements.
 Publication:

The Astronomical Journal
 Pub Date:
 June 2017
 DOI:
 10.3847/15383881/aa6ffd
 arXiv:
 arXiv:1612.02440
 Bibcode:
 2017AJ....153..257O
 Keywords:

 binaries: visual;
 methods: statistical;
 open clusters and associations: general;
 parallaxes;
 proper motions;
 stars: formation;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 published in AJ with minor revision