Chandra Detection of An Evolved Population of Young Stars in Serpens
  South
  We present a Chandra study of the deeply embedded Serpens South star-forming
region, examining cluster structure and disk properties at the earliest stages.
In total, 152 X-ray sources are detected. Combined with Spitzer and 2MASS
photometry, 66 X-ray sources are reliably matched to an IR counterpart. We
identify 21 class I, 6 flat spectrum, 16 class II, and 18 class III young
stars; 5 were unclassified. Eighteen sources were variable in X-rays, 8
exhibiting flare-like emission, and one periodic source. The cluster X-ray
luminosity distance was estimated, the best match was to the nearer distance of
260pc for the front of the Aquila Rift complex. The $N_{H}$ vs. $A_{K}$ ratio
is found to be $\sim$0.68x10$^{22}$, similar to that measured in other young
low mass regions, but lower than that measured in the ISM and high mass
clusters ($\sim$1.6-2x10$^{22}$). We find the spatial distribution closely
follows that of the dense filament from which the stars have formed, with the
class II population still strongly associated with the filament. There are four
sub-clusters in the field, with three forming knots in the filament, and a
fourth to the west, which may not be associated but may be contributing to the
distributed class III population. A high percentage of diskless class IIIs
(upper limit 30% of classified X-ray sources) in such a young cluster could
indicate that processing of disks is influenced by the cluster environment and
is not solely time-scale dependent.
