The molecular core associated with DR 21

Abstract

DR 21 has been observed in the J = 1-0 line of HCN with a resolution of 12.5 by 15.5 arcsec using the mm-wave interferometer at the Hat Creek Observatory. The HCN line is seen in both emission and absorption as an isolated clump immediately adjacent to the compact H II regions of DR 21. The full extent of the clump is about 30 arcsec in R.A. and 60 arcsec in decl. which corresponds to 0.3 by 0.6 pc for an assumed distance of 2 kpc. The mass of the clump is estimated to be about 200 solar masses. Two velocity components are present: the more intense one at -5 km/s is only seen in emission, and the other at -2.4 km/s is seen in emission in the northwest and mostly in absorption against the continuum source. The component at -5.0 km/s is identified to have higher excitation, and the one at -2.4 km/s to have greater column density.