AAS 201st Meeting, January, 2003
Session 17. Stellar Evolution and Metal-Poor Stars
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[17.10] VLBA Observations of the RS CVn Binary System \sigma Geminorum

D. A. Boboltz, A. L. Fey, K. J. Johnston (U.S. Naval Observatory)

We report the results of our VLBA observations of the RS CVn binary system \sigma Geminorum (HR 2973, HD 62044). \sigma Gem consists of a K1 III giant primary (MV = 4.15) and an unseen companion with an uncharacteristically long orbital period of ~19.6 days. In addition to strong Ca II H and K emission, the system exhibits the UV, X-ray, and radio emission typical of a chromospherically active binary. We observed the 8.4-GHz radio emission toward \sigma Gem as part of an astrometric VLBI experiment in March 2000 using the VLBA. The image produced from the full 6 hours of data shows several radio features including a strong compact feature at the phase center, and a weaker extended feature to the SE. There is also a marginal detection of a third feature to the NW of the central component with a peak ~12\sigma above the noise. To check for possible motions of the radio components, we divided the observations into three 2-hr, non-overlapping data sets and imaged each set individually. All three features are visible in the images produced from the subsets of the data. The SE radio feature was found to be moving to the north and inward toward the central feature, while the NW feature moved to the south and also inward. Physical implications of the component characteristics and motions are discussed along with the applicability of current models for the generation of radio emission from RS CVn binaries.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.