A VLT/NACO Study of Star Formation in the Massive Embedded Cluster RCW
  38
  We present adaptive optics (AO) near-infrared (JHKs) observations of the
deeply embedded massive cluster RCW 38 using NACO on the VLT. Narrowband AO
observations centered at wavelengths of 1.28, 2.12, and 2.17 micron were also
obtained. The area covered by these observations is about 0.5 pc square,
centered on the O star RCW 38 IRS2. We use the JHKs colors to identify young
stars with infrared excess. Through a detailed comparison to a nearby control
field, we find that most of the 337 stars detected in all three infrared bands
are cluster members (~317), with essentially no contamination due to background
or foreground sources. Five sources have colors suggestive of deeply embedded
protostars, while 53 sources are detected at Ks only; their spatial
distribution with respect to the extinction suggests they are highly reddened
cluster members. Detectable Ks-band excess is found toward 29 +/- 3 % of the
stars. For comparison to a similar area of Orion observed in the near-infrared,
mass and extinction cuts are applied, and the excess fractions redetermined.
The resulting excesses are then 25 +/- 5 % for RCW 38, and 42 +/- 8 % for
Orion. RCW 38 IRS2 is shown to be a massive star binary with a projected
separation of ~500 AU. Two regions of molecular hydrogen emission are revealed
through the 2.12 micron imaging. One shows a morphology suggestive of a
protostellar jet, and is clearly associated with a star only detected at H and
Ks, previously identified as a highly obscured X-ray source. Three spatially
extended cometary-like objects, suggestive of photoevaporating disks, are
identified, but only one is clearly directly influenced by RCW 38 IRS2. A King
profile provides a reasonable fit to the cluster radial density profile and a
nearest neighbor distance analysis shows essentially no sub-clustering.
