IN-SYNC. II. Virial Stars from Subvirial Cores—the Velocity Dispersion of Embedded Pre-main-sequence Stars in NGC 1333

Creators: Foster, Jonathan B.; Cottaar, Michiel; Covey, Kevin R.; Arce, Héctor G.; Meyer, Michael R.; Nidever, David L.; Stassun, Keivan G.; Tan, Jonathan C.; Chojnowski, S. Drew; Da Rio, Nicola; Flaherty, Kevin M.; Rebull, Luisa; Frinchaboy, Peter M.; Majewski, Steven R.; Skrutskie, Michael; Wilson, John C.; Zasowski, Gail

Abstract

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 ± 0.12 km s^(–1) after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s^(–1). Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 μG magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse.

Additional Information

© 2015 American Astronomical Society. Received 2014 September 19; accepted 2014 November 21; published 2015 January 22. J.B.F. performed the analysis contained herein and wrote the manuscript. M.C. developed and ran the spectral analysis routines producing the stellar parameters used in this paper. K.R.C., J.C.T., and M.R.M. conceived the program's scientific motivation and scope, led the initial ancillary science proposal, oversaw the project's progress, and contributed to the analysis of the stellar parameters; K.R.C. also led the target selection and sample design process and provided assistance with the analysis and interpretation of the APOGEE spectra. H.A.G. provided access to the dense gas data and help with interpreting the comparison between stellar and gas velocities. D.L.N. assisted in the interpretation of the APOGEE data products and reduction algorithms, particularly those related to radial velocity measurements. N.D.R. provided comparison with the gas and stellar velocities in Orion. K.M.F. assisted with target selection. K.G.S. contributed to the discussion of velocity spreads. S.D.C. and G.Z. oversaw the design of the APOGEE plates utilized for IN-SYNC observations. S.R.M., M.F.S., and P.M.F. contributed to defining the scope and implementation plan for this project and, with J.C.W., developed and provided high-level leadership for the broader APOGEE infrastructure and survey that enabled this science. L.R. contributed to the development of the input catalog for NGC 1333a. This research made use of Astropy, a community-developed core Python package for astronomy (Astropy Collaboration et al. 2013). This research has made use of NASA's Astrophysics Data System. We thank Stella Offner, Alyssa Goodman, Alvaro Hacar, Ralf Klessen, and Mark Heyer for insightful discussions. We thank our referees for insightful reports that improved this paper. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III Web site is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration, including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

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