Members of widely-separated stellar binaries (> 0.1 pc) or loosely bound stellar associations and clusters are born with small spreads in kinematics and chemistry, but disrupt and dissociate on timescales comparable to their orbital time within the Milky Way. The kinematic properties of comoving star pairs—bound wide binaries or unbound but coeval stars—are therefore sensitive to both the smooth tidal field and gravitational perturbation spectrum of the Milky Way. In previous work, we identified >4,000 candidate comoving pairs using only astrometric data from the Tycho-Gaia Astrometric Solution (TGAS) catalog and find a large number of pairs with separations > 1 pc. Without radial velocity measurements for the vast majority of these pairs, the false-positive rate at these separations is significant (~50%). Here we present results from our own low-resolution radial-velocity survey of a random sample of the candidate pairs to identify and validate true comoving star pairs. Of the 311 observed comoving pairs, we confirm 127 comoving pairs with separations as large as ~10 pc, our original search limit. Between separations of 0.001 pc to ~0.5 pc, the number of confirmed pairs per separation decreases with increasing separation (number per log separation is uniform). From ~0.5 pc to 10 pc, the number per separation is approximately uniform (number per log separation increases). We confirm the discovery of a population of comoving star pairs at very large separations, suggesting that disrupted wide binaries and stellar associations remain approximately spatially coherent.
A. Price-Whelan, S. Oh and D. Spergel
Wed, 13 Sep 17
Comments: 27 pages, 12 figures; submitted to AAS journals