The heliospheric hydrogen wall and astrospheres
Abstract
Charge exchange processes in the outer heliosphere produce a population of hot hydrogen gas within the heliosphere, creating a "hydrogen wall" in between the heliopause and bow shock. The heliospheric hydrogen wall scatters Ly photons passing through it, producing a detectable absorption signature in observations of Ly emission from nearby stars. This heliospheric absorption has been observed using observations from the Hubble Space Telescope (HST), and these observations have also yielded detections of analogous "astrospheric" absorption from material surrounding the observed stars. The astrospheric detections dramatize the importance of understanding the heliospheric interaction, since similar interactions exist around other stars and can now be detected and studied with HST. We present comparisons between the observed heliospheric absorption and the predictions of various kinetic and multifluid models in order to explore the constraints that the absorption can furnish for heliospheric models. The astrospheric absorption provides a way to empirically estimate the mass loss rates of solar-like stars, leading to the first empirical estimates of how solar-like winds vary with stellar age and activity. These estimates require the use of models, providing an important new application for heliospheric/astrospheric modeling. Finally, astrospheres are also potential sources of Ly emission as well as absorption. We present model Ly images of astrospheres and our heliosphere, and we also present HST's attempt to detect this emission around the star 40 Eri A.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E.836W