Observational Estimates for the Mass-Loss Rates of α Centauri and Proxima Centauri Using Hubble Space Telescope Lyα Spectra
Abstract
We study H I Lyα absorption observed by the Hubble Space Telescope toward the nearby binary system α Centauri (G2 V + K0 V) and its distant companion star Proxima Centauri (M5.5 Ve). Absorption from heliospheric H I heated by the solar wind/interstellar medium interaction is observed toward both α Cen and Proxima Cen. Absorption from analogous ``astrospheric'' material surrounding the stars is detected toward α Cen but not Proxima Cen. The nondetection of astrospheric absorption toward Proxima Cen suggests that the stellar wind of Proxima Cen must be significantly weaker than that of the α Cen system. We compute several hydrodynamic models of the astrospheres assuming different mass-loss rates in order to predict astrospheric Lyα absorption for comparison with the observations. The model that best matches the α Cen data has a mass-loss rate of M=2 Msolar, and the models suggest an upper limit of M<=0.2 Msolar for Proxima Cen. Finally, we note that the heliospheric absorption observed toward Proxima Cen in 2000 May is identical to the heliospheric absorption observed toward α Cen in 1995 May, implying that the structure of the outer heliosphere does not change significantly during the solar activity cycle. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2001
- DOI:
- 10.1086/318888
- arXiv:
- arXiv:astro-ph/0011153
- Bibcode:
- 2001ApJ...547L..49W
- Keywords:
-
- Hydrodynamics;
- Stars: Individual: Constellation Name: α Centauri;
- Stars: Individual: Constellation Name: Proxima Centauri;
- Stars: Winds;
- Outflows;
- Ultraviolet: ISM;
- Ultraviolet: Stars;
- Astrophysics
- E-Print:
- 11 pages, 3 figures