Department of Physics & Astronomy
University of New Mexico

Center for Astrophysics Research and Technologies Seminar Series

Probing the Galactic AGB population through infrared and SiO maser emission

Presented by Megan Lewis (UNM)

The mass-loss from evolved Asymptotic Giant Branch (AGB) stars enshrouds the central star in a circumstellar envelope (CSE) that redistributes most of the stellar light into the infrared (IR) regime of the spectrum. In the CSEs of oxygen-rich AGB stars molecules including SiO form, and under certain conditions maser emission from SiO can make AGB stars bright beacons at radio frequencies (e.g., 43 and 86 GHz). SiO masers are ideal observational probes of AGB sources, providing data on their sky positions, line-of-sight velocities, and CSE conditions all without extinction or reddening effects, even in the Galactic plane and bulge. The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey observes SiO emission in thousands of Galactic AGB stars, and the BAaDE IR selection, observation strategies, and calibration methods have enabled the efficient detection of nearly 10,000 maser sources with the VLA so far. The general characteristics of the BAaDE sample, including the extent of the maser detections as compared to previous observations, the completeness of the survey, and the accuracy of the derived velocities show that BAaDE is unmatched in probing stellar properties and dynamics in the bulge. Homogenizing the sample by identifying O-rich AGB sources in the catalog using IR data and follow-up radio spectra not only improves the sample, but also demonstrates the utility of SiO masers as tracers of certain stellar populations (namely thin-shelled O-rich AGB stars) throughout the Galaxy. Observational data from BAaDE are the state-of-the-art comparison for maser pumping models, and the statistical behavior of 43 GHz SiO masers in the sample exposes gaps in the understanding of SiO maser pumping and can guide future models.

2:00 pm, Thursday, April 1, 2021

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