Computer Science
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5879h&link_type=abstract
HST Proposal ID #5879
Computer Science
Hst Proposal Id #5879 Interstellar Medium
Scientific paper
We will use the GHRS to study the deuterium to hydrogen ratio in the local interstellar medium through observations of their interstellar absorption against the chromospheric HI Lyman-Alpha emission line of 7 nearby late-type stars. This method provides the only reliable determination of the D/H ratio in a setting where the processing of primordial deuterium is relatively well understood. Except for the observation of Linsky et al. (1993), all previous attempts to determine this ratio in the LISM have been compromised by poor signal-to-noise and insufficient instrumental resolution and the best numbers are on the order of 1.0times10^-5 implying a baryon density on the order of 1.0times10^-30 g cm^-3 in the universe. With observations of several stars in different directions we expect to determine the best value for the D/H ratio in the local interstellar medium and to either prove or lay to rest controversial claims of local variations in the ratio. As optical measurements have revealed several velocity components on scales of 5 pc and less in the LISM, we also plan to observe interstellar MgII and, where possible, FeII absorption lines against the same stars. These narrow features will allow us to discriminate between the different velocity components and thus model more precisely the interstellar HI absorption profile. We will thus also be able to place strong constraints on the column density, velocity dispersion, and bulk motion of the interstellar gas along many different lines of sight.
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