Star-forming Region Sh 2-233IR I. Deep NIR Observations toward the Embedded Stellar Clusters

TL;DR

This study used deep near-infrared observations to analyze the stellar populations, ages, and initial mass functions of subclusters within the Sh 2-233IR star-forming region, revealing sequential star formation and efficient star formation in certain subclusters.

Contribution

It provides new detailed near-infrared data and analysis of subcluster properties, including age, mass, and initial mass function slopes, highlighting sequential star formation and triggered cluster formation.

Findings

Subclusters have small age differences (~0.2-0.3 Myrs).

Initial mass function slopes are flatter than Salpeter, indicating more massive star formation.

High star formation efficiency (~40%) in the NE subcluster.

Abstract

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.