Hunting for Runaways from the Orion Nebula Cluster
Journal article, 2020

We use Gaia DR2 to hunt for runaway stars from the Orion Nebula Cluster (ONC). We search a region extending 45 degrees around the ONC and out to 1 kpc to find sources that have overlapped in angular position with the cluster in the last similar to 10 Myr. We find similar to 17,000 runaway/walkaway candidates that satisfy this 2D traceback condition. 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 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 Wide-field Infrared Survey Explorer photometry; (3) having a high degree of optical variability; (4) having closest approach distances well-constrained to within the cluster half-mass radius; (5) having ejection directions that avoid the main Galactic streaming contamination zone; and (6) having a required radial velocity (RV) for 3D overlap of reasonable magnitude (or, for the 7% of candidates with measured RVs, satisfying 3D traceback). Thirteen sources, not previously noted as Orion members, pass all these tests, while another twelve are similarly promising, except they are in the main Galactic streaming contamination zone. Among these 25 ejection candidates, ten with measured RVs pass the most restrictive 3D traceback condition. We present full lists of runaway/walkaway candidates, estimate the high-velocity population ejected from the ONC, and discuss its implications for cluster formation theories via comparison with numerical simulations.

Star formation

Runaway stars

Young star clusters

Stellar kinematics


Stellar dynamics


Juan Pablo Farias Osses

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Jonathan Tan

University of Virginia

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Laurent Eyer

University of Geneva

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 900 1 14

Subject Categories

Astronomy, Astrophysics and Cosmology


Geosciences, Multidisciplinary



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