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

[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.