Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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A NEAR-INFRARED STUDY OF THE HIGHLY-OBSCURED ACTIVE STAR-FORMING REGION W51B

  • Kim, Hyo-Sun (Department of Physics and Astronomy, Seoul National University) ;
  • Nakajima, Yasushi (National Astronomical Observatory of Japan) ;
  • Sung, Hwan-Kyung (Department of Astronomy and Space Science, Sejong University) ;
  • Moon, Dae-Sik (Division of Physics, Mathematics, and Astronomy, California Institute of Technology) ;
  • Koo, Bon-Chul (Department of Physics and Astronomy, Seoul National University)
  • Published : 2007.03.31
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Abstract

We present wide-field $JHK_s$-band photometric observations of the three compact H II 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 H II regions show the excess number of stars in the $J-K_s$ histograms compared with reference fields. While the mean color excess ratio $(E_{J-H}/E_{H-K_s})$ of the three compact H II regions are similar to ${\sim}2.07$, the visual extinctions toward them are somewhat different: ${\sim}17$ mag for G48.9-0.3 and G49.0-0.3; ${\sim}23$ mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is ${\leq}2\;Myr$. The inferred total stellar mass, ${\sim}1.4{\times}10^4M_{\odot}$, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of ${\sim}10%$.

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