We are indebted to Ewine van Dishoeck and David Jansen for providing us with their detailed radiative transfer models. We also thank the JCMT personnel, in particular Remo Tilanus, for their support and help in obtaining the observations discussed in this paper, and Jeroen Stil for considerable help in producing Fig. 2. The IRAM observations were kindly obtained for us by Gabriel Paubert in service mode.
© European Southern Observatory (ESO) 1999
Online publication: November 2, 1999