On the Variability of Radio Emission from MWC 349
Abstract
We analyze the results of 15-year monitoring of millimeter radio emission from MWC 349 in hydrogen recombination α-lines and in continuum made on the 12-m and 10-m radio telescopes of Arizona Radio Observatory (ARO). Both the masing lines and the continuum show large intensity variations, up to a factor of a few, at various time scales, from days to years. Other line parameters vary more moderately. In the best studied double-peaked H30α line, both the width of the peaks and their radial velocities (relative to the systemic velocity) vary within ±10%.The narrowness of the peaks and the rate of their intensity variations indicate that the H30α maser is essentially unsaturated. The observed single case of short-time scale correlated variability of H30α and the optical Hα line (the latter monitored with the Maria Mitchell Obs.’s 24-inch CCD telescope) confirms this conclusion. The changes of the “red” (R) and “blue” (B) peaks correlate but to varying extent, which indicates the presence of both a variable central source of excitation and the independently varying local conditions in the portions of the circumstellar disk where the B and R masers are assumed to arise. The variability pattern and the computer calculations of hydrogen level populations under the putative conditions in the disk allow us to estimate the unsaturated gain of the maser as |τ| ≈ 3±1. The observed anti-correlation of the B and R radial velocities for H30α and H35α lines confirms a common variable central source of excitation and the location of the masers at opposite sides of a (quasi)-Keplerian disk. We acknowledge with gratitude the TAC and the technical staff of ARO for the allocated time and help with the observations. This project was supported by NSF/REU grant AST-0851892 and the Nantucket Maria Mitchell Association.
- Publication:
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American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22114410P