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We will report here on our ongoing program to measure the deuterium/hydrogen (D/H) ratio and interstellar gas properties along many lines-of-sight through the local interstellar medium using the HST Goddard High Resolution Spectrograph. We have previously reported (ApJ 402, 694 (1993)) that for the line-of-sight towards Capella (12.5 pc, l=163$^{\circ}$, b=+5$^{\circ}$) that D/H = 1.65 (+0.07, -0.18) $\times10^{-5}$, T = $7,000\pm200$ K and the turbulent velocity is $1.66\pm0.03$ km s$^{-1}$. These quantities were determined by modeling the interstellar hydrogen and deuterium Lyman-$\alpha$ lines and the resonance lines of FeII and MgII against the background stellar emission line profiles.
We now report on the analysis of these spectral lines for the line-of-sight towards Procyon (3.5 pc, l=214$^{\circ}$, b=+13$^{\circ}$). Our new data set consists of very high signal-to-noise G160M spectra of the Lyman-$\alpha$ lines and Echelle spectra of the FeII 2599 \AA\ and MgII 2796, 2803 \AA\ lines. Comparison of these new data with those for the Capella line-of-sight will provide information on the nonuniformity of the local interstellar medium and begin to tell us whether the D/H ratio is constant or varies with line-of-sight in the local interstellar medium. We infer the primordial value of D/H from Galactic evolution models and comment on the inferred baryon density of the Universe.
This work is supported by NASA grants, including Interagency Transfer No. S-56460-D to the NIST.
