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Paper: The D/H Ratio towards PG 0038+199
Volume: 348, Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE
Page: 97
Authors: Williger, G.M.; Oliveira, C.; Hebrard, G.; Dupuis, J.; Dreizler, S.
Abstract: We determine the D/H ratio in the interstellar medium toward the DO white dwarf PG 0038+199 using spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE), with ground-based support from Keck H IRES. We employ curve of growth, apparent optical depth and profile fitting techniques to measure column densities and limits of many other species which allow us to determine related ratios such as D/O, D/N and the H2 fraction. We estimate a distance to PG 0038+199 of 297+164 −104 pc (1σ). We find column densities log N(H I) = 20.41±0.08, log N(D I) = 15.75±0.08 and log N(H2) = 19.33±0.04, yielding a molecular hydrogen fraction of 14±2% (all 2σ errors). [D I + HD]/[H I + 2H2] toward PG 0038+199 is 1.91+0:52−0.42 × 10−5 (2σ). There is no evidence of component structure on the scale of Δv > 8 km s−1 based on Na I, but there is marginal evidence for structure on smaller scales. The D/H value is high compared to the majority of recent D/H measurements, but consistent with the values for two other measurements at similar distances. D/O is in agreement with other distant measurements. The scatter in D/H values beyond ∼ 100 pc remains a challenge for Galactic chemical evolution.
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