http://arxiv.org/abs/2005.04762
We use Gaia DR2 to hunt for runaway and walkaway stars from the Orion Nebula Cluster (ONC). We search a large area of the sky extending 45$^\circ$ in radius around the ONC and out to a distance of 1 kpc to find sources that overlapped in angular position with the cluster in the last ~10 Myr, also accounting for the ONC’s own proper motion. We construct a main sample of ~17,000 runaway/walkaway candidates selected by this 2D traceback condition. However, most of these are expected to be contaminants, e.g., caused by Galactic streaming motions of stars at different distances. We thus examine six further tests or “flags” to help identify real runaways, namely: (1) possessing young stellar object (YSO) colors and magnitudes based on Gaia optical photometry; (2) having IR excess consistent with YSOs based on 2MASS and WISE photometry; (3) having a high degree of optical variability; (4) having closest approach distances to the ONC core well constrained within the half-mass radius of the cluster; (5) having direction of ejection from the ONC that avoids the main contamination zone due to Galactic streaming; and (6) having a required radial velocity (RV) for 3D overlap with the ONC that is of reasonable magnitude (or, for the small fraction, 7%, of candidate stars with Gaia measured RVs, satisfying 3D traceback). Thirteen sources, not previously noted as Orion members, pass all of these tests, while another twelve are similarly promising, except that they are located in the zone most contaminated by Galactic streaming. Among these 25 ejection candidates, there are ten with measured RVs that pass the most restrictive 3D traceback condition. We present full lists of runaway/walkaway candidate stars, estimate the high-velocity population ejected from the ONC and discuss its implications for star cluster formation theories via comparison with numerical simulations.
J. Farias, J. Tan and L. Eyer
Tue, 12 May 20
14/64
Comments: 22 pages, 10 figures and 5 tables. Submitted to ApJ, comments welcome