The D/H Ratio toward PG 0038+199

We determine the D/H ratio in the interstellar medium toward the DO whitedwarf PG0038+199 using spectra from the Far Ultraviolet Spectroscopic Explorer(FUSE), with ground-based support from Keck HIRES. We employ curve of growth,apparent optical depth and profile fitting techniques to measure columndensities and limits of many other species (H2, NaI, CI, CII, CIII, NI, NII,OI, SiII, PII, SIII, ArI and FeII) which allow us to determine related ratiossuch as D/O, D/N and the H2 fraction. Our efforts are concentrated on measuringgas-phase D/H, which is key to understanding Galactic chemical evolution andcomparing it to predictions from Big Bang nucleosynthesis. We find columndensities log N(HI) = 20.41+-0.08, log N(DI)=15.75+-0.08 and log N(H2) =19.33+-0.04, yielding a molecular hydrogen fraction of 0.14+-0.02 (2 sigmaerrors), with an excitation temperature of 143+-5K. The high HI column densityimplies that PG0038+199 lies outside of the Local Bubble; we estimate itsdistance to be 297 (+164,-104)pc (1 sigma). D/[HI+2H2] toward PG0038+199 is1.91(+0.52,-0.42) e-5 (2 sigma). There is no evidence of component structure onthe scale of Delta v > 8 km/s based on NaI, but there is marginal evidence forstructure on smaller scales. The D/H value is high compared to the majority ofrecent D/H measurements, but consistent with the values for two othermeasurements at similar distances. D/O is in agreement with other distantmeasurements. The scatter in D/H values beyond ~100pc remains a challenge forGalactic chemical evolution.Comment: 59 pages, 7 tables, 18 figures (1 standalone), accepted by ApJ v2 minor typos correcte