NEW RADIO RECOMBINATION MASER FEATURES AND CO OBSERVATIONS IN MWC349

We present observations of the J = 1 --> 0 line of CO and of the milli meter recombination lines H30alpha, H35alpha H38alpha and H39alpha tow ard the radio star MWC349. The profiles of the H35alpha and H39alpha l ines show new narrow features (linewidths of 15-20 km s-1 ) at radial velocities of -58 and 58 km s-1, 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 H35alpha line an d relatively weak in the H30alpha line) are inconsistent with LTE emis sion. Therefore these new high-velocity features are very likely radio recombination line masers (high-velocity masers). Contrary to the mil limeter recombination line masers previously discovered in this source at radial velocities of 30 and -14 km s-1 (low-velocity masers) whose intensity increases by a factor approximately 100 between the H39alph a and the H30alpha line, the high-velocity maser intensity increases b y only a factor of less than or similar to 10. We propose a two-compon ent model which qualitatively explains the radial velocities and the l ine intensity characteristics of the two kind of masers observed in th is source. In this model, the high-velocity masers arise from the ioni zed stellar wind and the low-velocity masers from the interface region of the ionized stellar wind and the neutral disk around MWC349. The r adial velocity separation of the low-velocity maser spikes as a functi on quantum number deviates from that expected for a disk in keplerian rotation. We have estimated the CO emission toward MWC349 by subtracti ng from the spectra of the blended CO and H38alpha line that of the H3 9alpha line. We detect a narrow (approximately 5 km s-1) absorption li ne plus a broad (linewidth of approximately 50 km s-1 ) emission. The broad emission is only tentatively detected because of the procedure u sed to derive it. We discuss the possible association of the CO featur es with neutral circumstellar material in MWC349.