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J.L. Linsky (JILA/Univ. Colorado), B.T. Draine (Princeton Univ.), H.W. Moos (JHU), E.B. Jenkins (Princeton Univ. Obs.), B.E. Wood (JILA/Univ. Colorado), C. Oliveira, W.P. Blair (JHU), S.D. Friedman (STScI), C. Gry (Lab. d'Astro. Marseille), D. Knauth (Northwestern Univ.), J.W. Kruk (JHU), S. Lacour (Obs. Paris-Meudon), N. Lehner (Univ. Wisconsin), S. Redfield (Univ. Texas), J.M. Shull (CASA/Univ. Colorado), G. Sonneborn (Lab. Obs. Cosmology/GSFC), G.M. Williger (JHU)
Analyses of spectra obtained with the FUSE satellite, together with spectra from the Copernicus and IMAPS instruments, reveal a very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond the Local Bubble (the region of space extending to roughly 100 pc from the Sun). For gas located beyond the Local Bubble but within several hundred parsecs, the observed D/H ratios differ by a factor of 4--5, which is difficult to explain solely on the basis of either: (i) small-scale spatial variations in stellar nuclear processes that convert deuterium to heavier elements; or (ii) the infall of deuterium-rich gas from the Galactic halo and the IGM. We argue instead that spatial variations in the depletion of deuterium onto dust grains can explain these local variations in the observed gas-phase D/H ratios. We present a variable deuterium depletion model that naturally explains the constant measured values of D/H inside the Local Bubble, the wide range of gas-phase D/H ratios observed in the intermediate regime (\log N(H~I) = 19.2--20.7), and the low gas-phase D/H ratios observed at larger hydrogen column densities. We test the deuterium depletion hypothesis by: (i) correlations of gas-phase D/H ratios with depletions of the refractory metals iron and silicon, and (ii) correlation with HD in heavily reddened lines of sight. Both of these tests are consistent with deuterium depletion from the gas phase in cold, not recently shocked, regions of the ISM, and high gas-phase D/H ratios in gas that has been shocked or otherwise heated recently. We argue that the total (gas plus dust) D/H ratio within 1 kpc of the Sun has a much larger value than D/H in the gas phase in the Local Bubble, indicating that over the lifetime of the Galaxy there has been a relatively small decrease in the total D/H ratio from its primordial value.
This work is based on observations made with the NASA-CNES-CSA FUSE satellite, which is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.