Does the D/H Ratio Vary in Local Interstellar Gas?

Details Does the D/H Ratio Vary in Local Interstellar Gas? Does the D/H Ratio Vary in Local Interstellar Gas?

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8595s&link_type=abstract

HST Proposal ID #8595

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Hst Proposal Id #8595 Ism And Circumstellar Matter

Scientific paper

Measurements of the D/H ratio in the Local Interstellar Cloud {LIC} are consistent with 1.5 +/- 0.1 X 10^-5, while for other clouds within 100 pc, the measurement uncertainties are larger. Current data provide limited information on whether the D/H ratio varies between the LIC and the other clouds. We propose to determine if the D/H ratio varies, by high- precision D/H measurements and by devising strategies to reduce both random and systematic errors. STIS E140H & E230H mode {R 150, 000} data will resolve the velocity components and allow reliable determinations of component-to-component variations. Two target white dwarfs {WDs} HZ 43 and GD 153 are chosen because EUVE data show low HI column densities, thereby reducing the probabilities of multiple velocity components and saturation of the DI line. The WDs have pure-H atmospheres, so contamination of the interstellar lines by photospheric metal lines is not an issue. Physically realistic NLTE models will be used to accurately predict the WD Lyman-Alpha contributions. HST-STIS, with its higher velocity resolution {compared to GHRS & FUSE}, wider wavelength coverage, and better scattered light corrections {compared to GHRS} is the facility best suited for this project. We have demonstrated the capabilities of STIS in our study of the G191-B2B sightline, which is the only published STIS measurement of the D/H ratio to date.

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