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Register a new userA Near-Infrared Study of the Highly-Obscured Active Star-Forming Region W51B
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We present wide-field JHKs-band photometric observations of the three compact HII regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact HII regions show the excess number of stars in the J-Ks histograms compared with reference fields. While the mean color excess ratio E(J-H)/E(H-Ks) of the three compact HII regions are similar to ~ 2.07, the visual extinctions toward them are somewhat different: ~ 17 mag for G48.9-0.3 and G49.0-0.3; ~ 23 mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact HII region is =< 2 Myr. The inferred total stellar mass, ~ 1.4 x 10^4 M_sun, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of ~ 10 %.
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We report the results of a near-infrared imaging study of a $7.8 times 7.8$ arcmin$^2$ region centered on the 6.7 GHz methanol maser associated with the RCW 34 star forming region using the 1.4m IRSF telescope at Sutherland. A total of 1283 objects were detected simultaneously in J, H, and K for an exposure time of 10800 seconds. The J-H, H-K two-colour diagram revealed a strong concentration of more than 700 objects with colours similar to what is expected of reddened classical T Tauri stars. The distribution of the objects on the K {it vs} J-K colour-magnitude diagram is also suggestive that a significant fraction of the 1283 objects is lower mass pre-main sequence stars. We also present the luminosity function for the subset of about 700 pre-main sequence stars and show that it suggests ongoing star formation activity for about $10^7$ years. An examination of the spatial distribution of the pre-main sequence stars shows that the fainter (older) part of the population is more dispersed over the observed region and the brighter (younger) subset is more concentrated around the position of the O8.5V star. This suggests that the physical effects of the O8.5V star and the two early B-type stars on the remainder of the cloud out of which they formed, could have played a role in the onset of the more recent episode of star formation in RCW 34.
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