Astronomy and Astrophysics, volume 288, L25-28 (1994/8-2)
Detection of H21α maser emission at 662GHz in MWC 349.
THUM C., MATTHEWS H.E., HARRIS A.I., TACCONI L.J., SCHUSTER K.F. and MARTIN-PINTADO J.
Abstract (from CDS):
We report the detection of maser emission towards MWC349 in the 662 GHz H21α line, by far the highest frequency radio recombination line (RRL) detected to date. The peak flux densities of the two maser spikes are a factor ∼1.7 stronger than those of the H26α transition at 354 GHz observed simultaneously. This increase and the accompanying increase of the widths of both spikes indicates that the degree of maser saturation is still increasing at quantum numbers n∼21. The broad pedestal emission has increased even more, by factors of 2-4 relative to the H26α pedestal, probably due to strong stimulated emission. The relative line enhancement is greatest at the extreme velocities from which we infer a velocity of 42 km/s for the ionized wind. The velocity separation of the H21α maser spikes is identical to that observed at H26α, confirming the apparent flattening of the disk rotation curve noted before. This may be explained by the disk being braked inside the H30α emission radius or by a situation where all RRL masers below n∼30 are emitted by essentially the same volume of gas.