Deep Near‐Infrared Observations of the W3 Main Star‐forming Region

We present a deep JHKs-band imaging survey of the W3 Main star formingregion, using the near-infrared camera, SIRIUS, mounted on the University ofHawaii 2.2m telescope. The near-infrared survey covers an area of ~ 24 sq.arcmin with 10 sigma limiting magnitudes of ~ 19.0, 18.1, and 17.3 in J, H, andKs-band, respectively. We construct JHK color-color and J/J-H and K/H-Kcolor-magnitude diagrams to identify young stellar objects and estimate theirmasses. Based on these color-color and color-magnitude diagrams, a richpopulation of YSOs is identified which is associated with the W3 Main region. Alarge number of previously unreported red sources (H-K > 2) have also beendetected around W3 Main. We argue that these red stars are most probablypre-main sequence stars with intrinsic color excesses. We find that the slopeof the Ks-band luminosity function of W3 Main is lower than the typical valuesreported for the young embedded clusters. The derived slope of the KLF is thesame as that found by Megeath et al. (1996), from which analysis by Megeath etal. indicates that the W3 Main region has an age in the range of 0.3--1 Myr.Based on the comparison between models of pre-main sequence stars with theobserved color-magnitude diagram we find that the stellar population in W3 Mainis primarily composed of low mass pre-main sequence stars. We also report thedetection of isolated young stars with large infrared excesses which are mostprobably in their earliest evolutionary phases.