Lyα Absorption from Heliosheath Neutrals
- 1 March 2007
- journal article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 657 (1), 609-617
- https://doi.org/10.1086/510844
Abstract
We assess what information HST observations of stellar Ly-alpha lines can provide on the heliosheath, the region of the heliosphere between the termination shock and heliopause. To search for evidence of heliosheath absorption, we conduct a systematic inspection of stellar Ly-alpha lines reconstructed after correcting for ISM absorption (and heliospheric/astrospheric absorption, if present). Most of the stellar lines are well centered on the stellar radial velocity, as expected, but the three lines of sight with the most downwind orientations relative to the ISM flow (Chi1 Ori, HD 28205, and HD 28568) have significantly blueshifted Ly-alpha lines. Since it is in downwind directions where heliosheath absorption should be strongest, the blueshifts are almost certainly caused by previously undetected heliosheath absorption. We make an initial comparison between the heliosheath absorption and the predictions of a pair of heliospheric models. A model with a complex multi-component treatment of plasma within the heliosphere predicts less absorption than a model with a simple single-fluid treatment, which leads to better agreement with the data. Finally, we find that nonplanetary energetic neutral atom (ENA) fluxes measured by the ASPERA-3 instrument on board Mars Express, which have been interpreted as being from the heliosheath, are probably too high to be consistent with the relative lack of heliosheath absorption seen by HST. This would argue for a local interplanetary source for these ENAs instead of a heliosheath source.Comment: 27 pages, 7 figures, AASTEX v5.0, accepted by ApThis publication has 29 references indexed in Scilit:
- ASPERA-3 on Mars ExpressIcarus, 2006
- Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary MediumThe Astrophysical Journal, 2006
- A model for the tail region of the heliospheric interfaceAstronomy Letters, 2003
- Determination of geometrical and kinematical properties of halo coronal mass ejections using the cone modelJournal of Geophysical Research, 2002
- Determination of accurate stellar radial-velocity measuresAstronomy & Astrophysics, 2002
- Energetic neutral atom imaging of the heliospheric boundary regionJournal of Geophysical Research, 2001
- Evaluating Possible Heating Mechanisms Using the Transition Region Line Profiles of Late‐Type StarsThe Astrophysical Journal, 1997
- Effect of local interstellar medium hydrogen fractional ionization on the distant solar wind and interface regionJournal of Geophysical Research, 1995
- A search for substellar companions to southern solar-type starsThe Astrophysical Journal, 1993
- The influence of the interface between the heliosphere and the local interstellar medium on the penetration of the H atoms to the solar systemThe Astrophysical Journal, 1991