Star-forming Region Sh 2-233IR I. Deep NIR Observations toward the
  Embedded Stellar Clusters
  We observed the Sh 2-233IR (S233IR) region with better sensitivity in
near-infrared than previous studies for this region. By applying statistical
subtraction of the back- ground stars, we identified member sources and derived
the age and mass of three distinguishable sub-groups in this region: Sh 2-233IR
NE, Sh 2-233IR SW, and the "distributed stars" over the whole cloud. Star
formation may be occurring sequentially with a relatively small age difference
(\sim 0.2-0.3 Myrs) between subclusters. We found that the slopes for initial
mass function (Gamma \sim -0.5) of two subclusters are flatter than that of
Salpeter, which suggests that more massive stars were preferentially formed in
those clusters compared to other Galactic star-forming regions. These
subclusters may not result from the overall collapse of the whole cloud, but
have formed by triggering before the previous star formation activities
disturbed the natal molecular cloud. Addi- tionally, high star formation
efficiency (&40%) of the subclusters may also suggest that stars form very
efficiently in the center of NE.
