THE NATURE OF THE RADIO RECOMBINATION LINE EMISSION FROM MWC 349A

This paper reports the detection of the H39 beta radio recombination line (RRL) (205 GHz) from the star MWC 349A. Comparison of this observation with the H40 alpha (99 GHz) line shows directly that the ''horn'' features of the previously detected H31 alpha (210 GHz), H30 alpha (232 GHz), and H29 alpha (256 GHz) lines are indeed strong RRL masers, thereby confirming inference made previously from time variations (Martin-Pintado et al.) and from radio interferometer observations (Planesas et al.). On the other hand, the H40 alpha, H39 beta, and the central ''pedestal'' emission of the H31-29 alpha lines appear to be emitted in near-LTE conditions on the basis of their relative intensities.