The alpha Centauri Line of Sight: D/H Ratio, Physical Properties of Local Interstellar Gas, and Measurement of Heated Hydrogen (The 'Hydrogen Wall') Near the Heliopause

Abstract

view Abstract Citations (234) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The α Centauri line of sight: D/H ratio, physical properties of local interstellar gas, and measurement of heated hydrogen (the "hydrogen wall") near the heliopause. Linsky, Jeffrey L. ; Wood, Brian E. Abstract The authors analyze high resolution spectra of the nearby (1.34 pc) stars α Cen A (G2 V) and α Cen B (K1 V), which were obtained with the GHRS on the HST. The observations consist of echelle spectra of the Mg II 2800 Å and Fe II 2599 Å resonance lines and the Lyman-α lines of hydrogen and deuterium. The interstellar gas has a velocity of v = -18.0±0.2 km s-1. The temperature and nonthermal velocity inferred from the Fe II, Mg II, and D I line profiles are T = 5400±500K and ξ = 1.20±0.25 km s-1, respectively. However, single component fits to the H I Lyman-α lines yield a Doppler parameter (bHI = 11.80 km s-1) that implies a significantly higher temperature of 8350K, and the velocity of the H I absorption is redshifted by about 2.2 km s-1 with respect to the Fe II, Mg II, and D I lines. The one component model of the interstellar gas suggests log NHI = 18.03±0.01 and D/H = (5.7±0.2)×10-6. The most sensible way to resolve the discrepancy between H I and the other lines is to add a second absorption component to the H I lines. This component is hotter, is redshifted relative to the primary component by 2 - 4 km s-1, and has a column density too low to be detected in the Fe II, Mg II, and D I lines. The authors propose that the gas responsible for this component is located near the heliopause, consisting of the heated H I gas from the interstellar medium that is compressed by the solar wind (the solar "hydrogen wall"). After considering the effects of a possible similar hydrogen wall around α Cen on the analysis, the authors derive for the solar hydrogen wall the parameters: log NHI = 14.74±0.24, bHI = 21.9±1.7 km s-1 (corresponding to T = 29,000±5000K) and vHI > -16 km s-1. Taking the solar hydrogen wall into account, the H I column density along the line of sight to α Cen is log NHI = 17.80±0.30, corresponding to nHI = 0.15 cm-3 (± a factor of 2), and D/H is in the range (0.5 - 1.9)×10-5. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177238 Bibcode: 1996ApJ...463..254L Keywords: Centaurus Constellation; Interstellar Matter; Interstellar Gas; Hydrogen; High Resolution; Chemical Properties; Hubble Space Telescope; Spectrographs; Temperature Measurement; D Lines; H Lines; Heliosphere; Lyman Alpha Radiation; Plasma Interactions; Solar Energy; Subgiant Stars; Solar Physics; Interstellar Matter: Deuterium; Interstellar Matter: UV Lines; Interstellar Matter: Solar Neighborhood; Heliosphere: Interstellar Clouds full text sources ADS | data products SIMBAD (10) MAST (1) ESA (1)