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

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[45.09] VLBI Imaging of the 3mm SiO Masers Around R Cassiopeia

G.R. Sivakoff (Brandeis University), R.B. Phillips, C.J. Lonsdale, S.S. Doeleman (MIT Haystack Observatory)

In Asymptotic Giant Branch and Mira-like stars, 3mm SiO masers allow observers to probe the inner region of the circumstellar envelope close to the photosphere. In December 1998, the v=1, J=2 to 1 SiO transition of R Cas was observed at 86.2 GHz using the joint resources of the CMVA and VLBA. The images presented here are the first multi-baseline VLBI images of SiO masers in R Cas, and reveal a loosely organized ring similar to those seen around the small number of SiO stars imaged at 7mm.

We discuss the mapping techniques used and analysis of the resulting high fidelity maps which reveal approximately 57 "families" of maser features, each with well defined spatial and velocity extent. Quantifiable characteristics of these components indicate complex stellar dynamics. At a velocity resolution of 0.1 km/s, several families show velocity coherence of up to 2 km/s. These dentification algorithms are being applied to test the lifetimes of families across multiple observing epochs, and our goal is to make more rigorous probes into the physical conditions within stellar mass loss envelopes.

This research was carried out under the Research Experiences for Undergraduates (REU) Program at Haystack. The REU and CMVA programs at Haystack are sponsored by the National Science Foundation.

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