IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity
  Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333
  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 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 sub-virial velocity dispersion of 0.5 km/s.
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 micro-Gauss
magnetic field acting on the dense cores, or be the signature of a cluster with
initial sub-structure undergoing global collapse.
