Local Interstellar Medium Properties and Deuterium Abundances for the Lines of Sight toward HR 1099, 31 Comae, β Ceti, and β Cassiopeiae
Abstract
We analyze Goddard High-Resolution Spectrograph data to infer the properties of local interstellar gas and the deuterium/hydrogen (D/H) ratio for lines of sight toward four nearby late-type stars--HR 1099, 31 Comae, β Ceti, and β Cassiopeiae. The data consist of spectra of the hydrogen and deuterium Lyα lines, and echelle spectra of the Mg II h and k lines toward all stars except β Cas. Spectra of the RS CVn-type spectroscopic binary system HR 1099 were obtained near opposite quadratures to determine the intrinsic stellar emission line profile and the interstellar absorption separately. Multiple-velocity components were found toward HR 1099 and β Cet. The spectra of 31 Com and β Cet are particularly interesting because they sample lines of sight toward the north and south Galactic poles, respectively, for which H I and D I column densities were not previously available.
The north Galactic pole appears to be a region of low hydrogen density like the ``interstellar tunnel'' toward ɛ CMa. The temperature and turbulent velocities of the local interstellar medium (LISM) that we measure for the lines of sight toward HR 1099, 31 Com, β Cet, and β Cas are similar to previously measured values (T ~ 7000 K and ξ = 1.0-1.6 km s-1). The deuterium/hydrogen ratios found for these lines of sight are also consistent with previous measurements of other short lines of sight, which suggest D/H ~ 1.6 × 10-5. In contrast, the Mg abundance measured for the β Cet line of sight [implying a logarithmic depletion of D(Mg) = +0.30 +/- 0.15] is about 5 times larger than the Mg abundance previously observed toward α Cen, and about 20 times larger than all other previous measurements for the LISM. These results demonstrate that metal abundances in the LISM vary greatly over distances of only a few parsecs. 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 1997
- DOI:
- 10.1086/303449
- Bibcode:
- 1997ApJ...474..315P
- Keywords:
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- Stars: Binaries: Spectroscopic;
- ISM: Abundances;
- ISM: Clouds;
- Ultraviolet: ISM