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J.E. Andrews (Col. of Charleston & Maria Mitchell Obs.), V. Strelnitski (Maria Mitchell Obs.)
We present an analysis of variability over a period of seven years of the millimeter-wavelength continuum and line emission from the unique emission-line star MWC349. This variability is strongly supported by the correlations between the independently observed spectral features.
The intensity variations occur over various time scales. For the masing spectral features, the amplitude of variations attains 100% or more on a time scale of a year and drops to about 20% on a time scale of a month. The shortest, marginally detected variations, on a time scale of a day, do not surpass 10%. The ratio of the blue (B) and red (R) masing spectral peaks (these peaks arise at the opposite sides of the edge-on circumstellar disk) is measured more accurately than the absolute intensities of the peaks. The variations of the B/R ratio suggest quasi-periodic oscillations whose amplitude is roughly proportional to the period.
Correlations and anti-correlations between the radial velocities of the B and R peaks of the H30\alpha line can be explained by a variable central source of pumping rotating with a period of 2-3 months and lacking axial symmetry. Gigantic star spots could be the cause of the asymmetry. A ring (possibly protoplanetary) of variable width and density rotating around the center at the radius of the masing can explain the difference in the peaks' intensity (the B peak tends to be weaker). It can also account for the overall change of their radial velocities, indicating that during the past seven years the region responsible for the R peak was steadily approaching the center and the region responsible for the B peak was moving away. This project was supported by the NSF/REU grant AST-0354056 and the Nantucket Maria Mitchell Association.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.