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Session 45 - Interstellar Medium I.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
We present new GHRS observations of the Lyman-\alpha lines of \epsilon Indi (K5 V) and \lambda Andromedae (G8 IV-III + ?). Analysis of the interstellar H I and D I absorption lines reveals that the velocities and temperatures inferred from the H I lines are inconsistent with the properties of the D I lines, unless the H I absorption is assumed to consist of two absorption components. For both lines of sight, one absorption component is produced by interstellar material, with velocities consistent with those predicted by the local flow vector. For the 3.46 pc (23 pc) line of sight to \epsilon Ind (\lambda And), the average density for the interstellar medium is found to be n_H I=0.094\pm 0.022 cm^-3 (n_H I=0.040\pm 0.014 cm^-3).
We believe hot hydrogen surrounding \epsilon Ind and \lambda And is responsible for the second H I absorption component. These ``hydrogen walls'' are produced by the interaction of the winds of these stars with the surrounding interstellar material. An analogous solar hydrogen wall has been predicted by recent models of the heliospheric interface region and confirmed by GHRS observations of \alpha Cen. The temperatures we measure for the second components are 100,000\pm 20,000 and 62,000\pm 18,000 K for \epsilon Ind and \lambda And, respectively. These temperatures are too hot for the solar hydrogen wall, and for \epsilon Ind the velocity of the second component is clearly inconsistent with the solar hydrogen wall. Thus, we assume a stellar origin for these components, where the higher temperatures are a consequence of higher interstellar wind velocities in the stellar rest frames. Because the heliospheric models demonstrate the importance of a hot wind in the formation of the solar hydrogen wall, our detection of analogous structures around \epsilon Ind and \lambda And may constitute a first detection of solar-like winds around dwarf and subgiant stars.
This work was sponsored by NASA Interagency Transfer S-56460-D to the National Institute of Standards and Technology
