IN-SYNC. V. Stellar Kinematics and Dynamics in the Orion A Molecular Cloud

Abstract

The kinematics and dynamics of young stellar populations enable us to test theories of star formation. With this aim, we continue our analysis of the SDSS-III/APOGEE IN-SYNC survey, a high-resolution near-infrared spectroscopic survey of young clusters. We focus on the Orion A star-forming region, for which IN-SYNC obtained spectra of ∼2700 stars. In Paper IV we used these data to study the young stellar population. Here we study the kinematic properties through radial velocities (v r ). The young stellar population remains kinematically associated with the molecular gas, following a~-10 km s 1 gradient along the filament. However, near the center of the region, the v r distribution is slightly blueshifted and asymmetric; we suggest that this population, which is older, is slightly in the foreground. We find evidence for kinematic subclustering, detecting statistically significant groupings of colocated stars with coherent motions. These are mostly in the lower-density regions of the cloud, while the ONC radial velocities are smoothly distributed, consistent with it being an older, more dynamically evolved cluster. The velocity dispersion s v varies along the filament. The ONC appears virialized, or just slightly supervirial, consistent with an old dynamical age. Here there is also some evidence for ongoing expansion, from a v r -extinction correlation. In the southern filament, s v is ∼2-3 times larger than virial in the L1641N region, where we infer a superposition along the line of sight of stellar subpopulations, detached from the gas. In contrast, s v decreases toward L1641S, where the population is again in agreement with a virial state.

The APOGEE-2 Survey of the Orion Star-forming Complex. II. Six-dimensional Structure

“…While the pipeline does try to interpolate between grid points, it is less successful in some regimes than others (mainly with respect to T ef f ), and particular val- Comparison of T ef f and log g between the correlations produced with various grids. First row shows comparison with the results from Cottaar et al (2014) andDa Rio et al (2016), second row is restricted to sources in Pleiades (plateau is from the Coelho grid edges), bottom row includes sources that were observed by APOGEE towards the observed star forming regions that have both T ef f and log g produced in the ASPCAP catalog (which limits the sample primarily to the background red giants).…”

Is stellar multiplicity universal? Tight stellar binaries in the Orion Nebula Cluster

“…As-suming random directions for the traveling directions of systems, the encounter velocity can be approximated as twice the velocity dispersion of the population. Given the current velocity dispersion in the cluster (≈2 km s −1 ; Da Rio et al 2017), this implies that systems with orbital velocities of 4 km s −1 can survive contemporary and future interactions in the cluster. Assuming a mean system mass of 1.5 M and circular orbits, this orbital velocity corresponds to a semimajor axis of ≈80 au.…”

Gaia stellar kinematics in the head of the Orion A cloud: runaway stellar groups and gravitational infall

“…However, recent studies of star kinematics in Orion A find no evidence for star contraction. Da Rio et al (2017) provide signs of star expansion in the ONC based on the correlation between source extinction and radial velocities derived via near-IR Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectroscopy. The Gaia-APOGEE study of the Orion Complex including Orion A by Kounkel et al (2018) reports random stellar motions across ONC with "slight preference for expansion near the outer edges".…”