The observations were made with the SAO 6 m telescope operated by the Special Astrophysical Observatory, Russia. We thank R. Oudmaijer for valuable discussions on this outstanding object and M.A.T. Groenewegen for providing us with the `1992' data set of the SED. The radiative-transfer calculations are based on the code DUSTY developed by . Ivezi, M. Nenkova and M. Elitzur. A. Gauger and A. Men'shchikov are thanked for various discussions on radiative transfer problems. We are grateful to the referee for instructive remarks.
© European Southern Observatory (ESO) 1999
Online publication: August 13, 199