Hunting for Runaways from the Orion Nebula Cluster

Abstract

We use Gaia DR2 to hunt for runaway stars from the Orion Nebula Cluster (ONC). We search a region extending 45° around the ONC and out to 1 kpc to find sources that have overlapped in angular position with the cluster in the last ∼10 Myr. We find ∼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.

The Villafranca catalog of Galactic OB groups

“…We have searched the Gaia EDR3 astrometry and found five walkaway/runaway candidates. Two of them, V1321 Ori and Brun 334, are listed as K stars in Skiff (2014) and were already identified as runaways by Schoettler et al (2020) and Farias et al (2020). For another two, BD −05 1322 (with different spectral classifications listed in Skiff 2014, some of them indicating broad lines) and HU Ori we have found no prior identifications as walkaways/runaways.…”

“…The literature on runaway (and walkaway) stars from Villafranca O-023 reaches to the 1950s, as the prototype dynamical ejection that expelled AE Aur, µ Col, and ι Ori (Blaauw & Morgan 1954;Hoogerwerf et al 2000;Maíz Apellániz et al 2018b) took place there 2.5 Ma ago. Recent analyses have been carried out using Gaia DR2 (Schoettler et al 2020;Farias et al 2020) and HST (Platais et al 2020) data. We have searched the Gaia EDR3 astrometry and found five walkaway/runaway candidates.…”

A gravitational and dynamical framework of star formation: The Orion Nebula

“…This is similar to the typical velocity of the stars that are expanding away that we observe. Comparatively, true high velocity walkaway and runaway stars are rare, though, there are several dozen that are currently known to be associated with the ONC (McBride & Kounkel 2019;Schoettler et al 2020;Farias et al 2020). As such, hundreds of stars with lower ejection velocity are expected.…”

Constraints on star formation in NGC 2264

“…This earlier work focused exclusively on the spatial information, such as the overall structure (Cartwright & Whitworth 2004;Cartwright 2009) and the amount of mass segregation (Allison et al 2009) or relative surface densities (Maschberger & Clarke 2011;Parker et al 2014). The Gaia satellite has facilitated a vast improvement in these comparisons by enabling the proper motions of runaway stars to be used as dynamical tracers of the regions' past evolution (Schoettler et al 2019;Farias et al 2020;.…”