AAS 195th Meeting, January 2000
Session 45. Stellar Diameters and Circumstellar Material
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

## [45.07] On the Nature of the Masing Circumstellar Disk in MWC349

L.J. Jisonna Jr. (U. Arizona & Maria Mitchell Observatory), M. Gordon (NRAO), V. Strelnitski (Maria Mitchell Observatory)

We use the results of a 2-year monitoring of the masing component of two millimeter recombination lines of MWC349, H30\alpha and H35\alpha, for obtaining information about the structure and kinematics of the masing circumstellar disk and the physics of the maser process. The blue'' (B) and red'' (R) masing peaks in the H30\alpha line are comparable in intensity, whereas the blue component of the H35\alpha line is always considerably weaker than the red. We explain this by the inhomogeneity of the masing disk. Time variations of the B/R ratio in both lines correlate. This is explained by the interlocking of different masing lines, so that the strongest of them can influence the others. We reveal at least three time scales of B/R variations in the stronger, H30\alpha line and the proportionality of the amplitude of variations to the time scale. This is tentatively explained by the non-linear self-oscillations of maser intensity in a ring maser caused by the competition of maser modes for pumping. We confirm previously established anti-correlation of the radial velocities of the B and R peaks. This is naturally explained by the change of the effective radius of the masing ring due to the change of the intensity of the pumping from the star. However, we also reveal periods where the radial velocities of the two peaks correlate, which means that the two projected masing chords in the Keplerian disk move in the same direction relative to the central star (one approaching the star and the other receding from it). This asymmetry can be due to anisotropy of the radiative pumping of the masing disk by the rotating central star. It also may indicate a close-binary nature of MWC349A. One of the most enigmatic new facts is the monotonic increase of the systemic radial velocity as indicated by the H30\alpha line (but not by the H35\alpha line).

This project was supported by the NSF/REU grant AST-9820555.

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