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S. Moringello (Vassar College \& Maria Mitchell Obs.), M. Gordon (NRAO), V. Strelnitski (Maria Mitchell Obs.)
The double-peaked profiles of masing hydrogen millimeter recombination lines in MWC349 were previously shown to originate from opposite sides of a circumstellar Keplerian disk seen edge-on. We have monitored the H30\alpha and H35\alpha lines in MWC349 with the 12-m telescope of NRAO. The frequent (2-3 times a month), long integration time observations in the period from December 1997 to June 1998 allowed us to reveal a probable periodic component in the variations of the Blue/Red peak intensity ratio of the H30\alpha line, with a period of 84 +/- 3 days. The amplitude of the periodic component makes about +/- 10% of the peaks' intensity. The less precise data for the weaker, double-peaked masing component of the H35\alpha line seem to agree with this conclusion. These results confirm and quantitatively specify the periodicity of the B/R ratio suggested by Thum et al. in 1992. Our preliminary results for a longer observational period indicate possible interruptions of this oscillatory regime, which seem to correlate with the intensity of masing. We propose that the periodic variations of the B/R ratio are due to auto-oscillations of spatial maser modes competing for pumping in a disk maser. The interruptions in the periodic behavior can be due to destruction of the auto-oscillatory regime when the intensity of the pumping goes beyond certain limits.
The author(s) of this abstract have provided an email address for comments about the abstract: vladimir@mmo.org