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C. M. Oliveira, H. W. Moos (Johns Hopkins University), G. Hebrard (Institut d'Astrophysique de Paris), D. C. Knauth (Northwestern University)
Observations of the deuterium abundance, D/H, in the interstellar medium provide important constraints on Galactic chemical evolution models as well as on the Big Bang nucleosynthesis theory.
Recent results from FUSE have shown that for sightlines with log N(H) > 20.7, D/H is approximately half of that in the Local Bubble (D/HLB ~ 1.6E-5), with large variations for sightlines with N(H) larger than the Local Bubble but smaller than ~ 20.7. These results, in conjunction with results obtained with other observatories such as Copernicus and IMAPS, have questioned the previously held assumption that D/HLB is representative of the present-epoch abundance of deuterium. The causes of the low D/H at high N(H) as well as of the variations in the intermediate N(H) range are currently unknown. Depletion onto dust grains, infall of metal-poor gas and variable astration are mechanisms being considered to explain the D/H variations. However, the small number of sightlines with log N(H)> 20.7 for which D/H has been measured limits progress in this area.
In this work we use new FUSE data to derive column densities of DI, NI, OI, FeII and other species along three sightlines with log N(H) > 20.9, probing gas over distances larger than 1 Kpc. In conjunction with N(HI) derived from IUE data we compute D/H, N/H, O/H, and Fe/H ratios which are then compared to values in the literature.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by The Johns Hopkins University. Financial support to U. S. participants has been provided in part by NASA contract NAS5-32985 to Johns Hopkins University.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.