Observations of maser RRLs from the star MWC 349A

Abstract

Observations of H29α, H30α, and H31α radio recombination lines (RRLs) with rest frequencies 256 GHz, 232 GHz, and 210 GHz, respectively, from the star MWC 349A show variations in intensity and radial velocity over a period of 2.5 yrs. The data are consistent with a model of a star with a circumstellar disk embedded within an expanding, ionized atmosphere. Presumably, outbursts on the surface of the the star itself would cause changes in the circumstellar disk, which would affect the intensities of the RRLs. In this model the double-peaked profiles seen at mmwave frequencies would originate from 2 regions on opposite sides of a circumstellar disk in Keplerian motion, each region lying at a radius of ≈ 30 AU from the star. The separation of the emitting regions would then be ≈ 60 AU. The average radial velocity of the 2 peaks marks the radial velocity of the central star MWC 349A. At lower frequencies, the masing would subside. The increased opacity of the ionized wind would absorb the weakened RRLs from the disk and, correspondingly, generate increasingly visible RRLs from the stellar wind.

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