Computer Science
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5893v&link_type=abstract
HST Proposal ID #5893
Computer Science
Hst Proposal Id #5893 Interstellar Medium
Scientific paper
The proposed observations are the necessary continuation of an approved Cycle 1 proposal aiming at deriving the deuterium abundance in the local interstellar medium toward nearby hot stars. The present D/H ratio within the galaxy is one of the key-parameters of galactic evolution models. Although a very accurate measurement of the interstellar D/H ratio was made recently toward Alpha Aur using HST-GHRS (Linsky et al., 1993), it seems to us that the value of the present D/H ratio is not settled as yet. Many data set, as well as our recent Cycle 1 data toward G191-B2B, have suggested the possible existence of variations of this ratio, which might have some consequence on the galactic evolution of deuterium. These same Cycle 1 data seem to indicate also that a refined estimate of the Linsky et al. value should lie closer to 1.4 times 10^-5 than to 1.7 times 10^-5. We propose to carry out new and highly accurate measurements of the D/H ratio in the local medium by complementing our Cycle 1 observations toward G191-B2B with observations of two extremely important spectral regions using the Ech-A grating, namely the N I triplet (1200Angstrom) and the Lyman-alpha line where our previous G160M grating prevented us from constraining more tightly the D/H ratios. The efficiency and the availability of the Ech-A grating, as well as the quality of our already acquired data provides exceptional opportunities for carrying out precise measurements of D/H ratios in a relatively short integration time.
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