Astronomy and Astrophysics, volume 286, 890-897 (1994/6-3)
New radio recombination maser features and CO observations in MWC349.
MARTIN-PINTADO J., NERI R., THUM C., PLANESAS P. and BACHILLER R.
Abstract (from CDS):
We present observations of the J=1-0 line of CO and of the millimeter recombination lines H30α, H35α, H38α and H39α toward the radio star MWC349. The profiles of the H35α and H39α lines show new narrow features (linewidths of 15-20 km/s ) at radial velocities of -58 and 58 km/s , close to the terminal velocity of the ionized wind. These features are time variable and their intensities for different quantum numbers (strong emission in the H35α line and relatively weak in the H30α line) are inconsistent with LTE emission. Therefore these new high-velocity features are very likely radio recombination line masers (high-velocity masers). Contrary to the millimeter recombination line masers previously discovered in this source at radial velocities of 30 and -14km/s (low-velocity masers) whose intensity increases by a factor ∼100 between the H39α and the H30α line, the high-velocity maser intensity increases by only a factor of ≲10. We propose a two-component model which qualitatively explains the radial velocities and the line intensity characteristics of the two kind of masers observed in this source. In this model, the high-velocity masers arise from the ionized stellar wind and the low-velocity masers from the interface region of the ionized stellar wind and the neutral disk around MWC349. The radial velocity separation of the low-velocity maser spikes as a function quantum number deviates from that expected for a disk in keplerian rotation. We have estimated the CO emission toward MWC349 by subtracting from the spectra of the blended CO and H38α line that of the H39α line. We detect a narrow (∼5km/s ) absorption line plus a broad (linewidth of ∼50km/s ) emission. The broad emission is only tentatively detected because of the procedure used to derive it. We discuss the possible association of the CO features with neutral circumstellar material in MWC349.