Observations of maser RRLs from the star MWC 349A

Abstract

Observations of H29-alpha, H30-alpha, and H31-alpha 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 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 mm-wave frequencies would originate from two regions on opposite sides of a circumstellar disk in Keplerian motion, each region lying at a radius of about 30 AU from the star. ^The separation of the emitting regions would then be about 60 AU. ^The average radial velocity of the two 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. ^(Author (revised))