KINEMATICS OF THE ORION NEBULA CLUSTER: VELOCITY SUBSTRUCTURE AND SPECTROSCOPIC BINARIES

We present a kinematic study of the Orion Nebula Cluster (ONC) based upon RVs measured by multifiber echelle spectroscopy at the 6.5 m MMT and Magellan telescopes. Velocities are reported for 1613 stars, with multi-epoch data for 727 objects as part of our continuing effort to detect and analyze spectroscopic binaries (SBs). We confirm and extend the results of Furesz et al. showing that the ONC is not relaxed, consistent with its youth, and that the stars generally follow the position–velocity structure of the moderate density gas in the region, traced by 13CO. The additional RVs we have measured enable us to probe some discrepancies between stellar and gaseous structure which can be attributed to binary motion and the inclusion of nonmembers in our kinematic sample. Our multi-epoch data allow us to identify 89 SBs; more will be found as we continue monitoring. Our results reinforce the idea that the ONC is a cluster in formation, and thus provide a valuable testing ground for theory. In particular, our observations are not consistent with the quasi-equilibrium or slow contraction models of cluster formation, but are consistent with cold collapse models.