AAS 197, January 2001
Session 8. Circumstellar Matter and Winds
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[8.04] Using Astrospheric Ly\alpha Absorption Observed by HST to Study the Stellar Winds of \alpha~Cen~AB and Proxima~Cen

B.E. Wood, J.L. Linsky (JILA/Univ. Colo.), H.-R. Mueller, G.P. Zank (Bartol Res. Inst.)

Using HST observations of the nearby \alpha~Cen~AB binary system (G2~V+K0~V) and its distant companion star Proxima~Cen (M5.5~Ve), we study H~I Ly\alpha absorption produced by heated neutral hydrogen gas in the heliosphere, and we also study absorption from analogous ``astrospheric'' material surrounding the stars. We use these data to show how astrospheric Ly\alpha absorption allows us for the first time to estimate the properties of solar-like stellar winds. Unlike \alpha~Cen~AB, no astrospheric absorption whatsoever is detected toward Proxima Cen, suggesting that Proxima~Cen's wind must be significantly weaker than that of the \alpha~Cen~AB system. Hydrodynamic models of the astrospheres are computed assuming different mass-loss rates to determine which predict the correct amount of H~I absorption, and these studies suggest a mass-loss rate of \dot{M} \approx 2~\dot{M}\odot for \alpha~Cen~AB and \dot{M} \leq 0.2~\dot{M}\odot for Proxima~Cen.

Support for this work is provided by NASA grants NAG5-9041 and S-56500-D to the University of Colorado.

The author(s) of this abstract have provided an email address for comments about the abstract: woodb@casa.colorado.edu

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