Deuterium in the Line of Sight Towards Procyon and its Cosmological Significance

Astronomy and Astrophysics – Astronomy

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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(deg) , b=+5(deg) ) that D/H = 1.65 (+0.07, -0.18) *E(-5) , T = 7,000+/-200 K and the turbulent velocity is 1.66+/-0.03 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(deg) , b=+13(deg) ). 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 Angstroms and MgII 2796, 2803 Angstroms 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.

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