The Spatial Distribution of SiO Masers in AGB Stars at 43 and 86 GHz

Details The Spatial Distribution of SiO Masers in AGB Stars at 43 and 86 GHz The Spatial Distribution of SiO Masers in AGB Stars at 43 and 86 GHz

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...199.9214m&link_type=abstract

American Astronomical Society, 199th AAS Meeting, #92.14; Bulletin of the American Astronomical Society, Vol. 33, p.1442

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We present Very Long Baseline Interferometric (VLBI) images of the SiO masers near χ Cyg obtained with the Very Long Baseline Array (VLBA). VLBI observations of SiO masers provide information on the structure and dynamics of the inner circumstellar shells near AGB stars. These stars return large quantities of their stellar material to the interstellar medium during the AGB evolutionary stage. SiO masers occur in the innermost regions of the circumstellar shells, just a few stellar radii above the photosphere where the mass loss initiates and are therefore important to understand. For several years, a mild controversy has arisen over whether the v=1 and v=2, J=1 \sbond 0 and J=2 \sbond 1 SiO maser transitions all arise from the same or spatially distinct regions. This is critical for understanding whether collisional or radiative pumping drives the population inversion that sustains the maser radiation. However, because SiO masers change significantly over short timescales, the observations of the transitions must be made nearly simultaneously, a challenging feat for ad hoc VLBI arrays. The high quality 43 GHz performance of the VLBA combined with its newly developed 86 GHz observational capability has allowed us to simultaneously observe multiple SiO maser transitions at 43 and 86 GHz near the stars χ Cyg, TX Cam and R Cas, including some transitions of 29SiO. In this poster, we present maps of some of the transitions observed towards χ Cyg and our initial interpretation of the observations. This project would have been impossible without the upgraded high frequency capability of the VLBA, funded by the National Science Foundation and the hard work of the staff of the National Radio Astronomy Observatory to get the 86 GHz system up and running.

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