Physics
Scientific paper
Jul 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009hst..prop12287f&link_type=abstract
HST Proposal ID #12287. Cycle 18
Physics
Scientific paper
Measuring the abundance of deuterium relative to hydrogen in the interstellar medium provides a method to assess the effects of astration and subsequent chemical enrichment of the ISM by supernovae, massive star winds, infalling gas, and mixing. It is now well established that the gas phase of D/H is approximately constant within the Local Bubble, where log{N{HI}} < 19.2. At higher column densities D/H is highly variable, which has been attributed to varying levels of depletion of deuterium onto dust grains and enhancement due to the infall of low-metallicity, deuterium-rich material onto the Galaxy. We request observations of the Lyman-alpha profiles of 17 targets with the focused goal of reducing the greatest contribution to the error in Galactic D/H measurements: the poor determination of N{HI}. We will reduce the error on log N{HI} by an average of nearly a factor of 4. For all targets excellent measurements of N{DI} have already been made from FUSE observations. These new data will leverage off the more than 3 million seconds FUSE devoted to its deuterium program and give far more secure estimates of the level of spatial variability of gas-phase D/H. For 5 targets we will also observe metal lines of O I, Mn II, Mg II, Ni II, and possibly P II. Utilizing a new depletion unification method we will extend previous studies of the expected correlation between observed D/H and levels of depletion of many refractory elements, and this analysis can be applied to the remaining targets if at least one metal column density is known. These results will permit us to substantially improve constraints on models of galactic chemical evolution, including the degree of astration of gas in the Milky Way, relative to primordial estimates of D/H.;
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