LOCAL INTERSTELLAR MEDIUM PROPERTIES AND DEUTERIUM ABUNDANCES FOR THE LINES OF SIGHT TOWARD HR 1099, 31 COMAE, β CETI, AND β CASSIOPEIAE

摘要

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 ε 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 x 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.