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Session 63 - Stars and A Radio Source.
Oral session, Tuesday, January 14
Harbour C,
SiO maser emission provides a unique probe of both the kinematics and magnetic field structure in the extended atmospheres of late-type stars. Recent Very Long Baseline Interferometry (VLBI) observations of the SiO masers towards several late-type stars show that they are confined to a narrow ring-like morphology and typically lie within 2--4 stellar radii of the center of the star. Using NRAO's Very Long Baseline Array (VLBA), we have obtained 5 epochs of full-polarization observations of the v=1, J=1-0 SiO maser emission towards the Mira variable in the symbiotic binary R Aqr. These observations occurred at various phases in the stellar pulsation cycle allowing us to monitor variations in both the structure and the polarization of the maser emission with time. We find the SiO masers towards R Aqr lie in a ring-like distribution with a radius of \sim3.5 AU (\sim2 R_\ast). In addition, both the polarization and the structure of the maser emission vary significantly over timescales of \sim1--2 months.
