Astrophys. J., 609, 838-853 (2004/July-2)
Two new low galactic D/H measurements from the Far Ultraviolet Spectroscopic Explorer.
WOOD B.E., LINSKY J.L., HEBRARD G., WILLIGER G.M., MOOS H.W. and BLAIR W.P.
Abstract (from CDS):
We analyze interstellar absorption observed toward two subdwarf O stars, JL 9 and LS 1274, using spectra taken by the Far Ultraviolet Spectroscopic Explorer (FUSE). Column densities are measured for many atomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, Fe II, and H2), but our main focus is on measuring the D/H ratios for these extended lines of sight, as D/H is an important diagnostic for both cosmology and Galactic chemical evolution. We find D/H=(1.00±0.37)x10–5 toward JL 9 and D/H=(0.76±0.36)x10–5 toward LS 1274 (2 σ uncertainties). With distances of 590±160 and 580±100 pc, respectively, these two lines of sight are currently among the longest Galactic lines of sight with measured D/H. With the addition of these measurements, we see a significant tendency for longer Galactic lines of sight to yield low D/H values, consistent with previous inferences about the deuterium abundance from D/O and D/N measurements. Short lines of sight with H I column densities of logN(HI)<19.2 suggest that the gas-phase D/H value within the Local Bubble is (D/H)LBg=(1.56±0.04)x10–5. However, the four longest Galactic lines of sight with measured D/H, which have d>500 pc and logN(HI)>20.5, suggest a significantly lower value for the true local disk gas-phase D/H value, (D/H)LDg=(0.85±0.09)x10–5. One interpretation of these results is that D is preferentially depleted onto dust grains relative to H and that longer lines of sight that extend beyond the Local Bubble sample more depleted material. In this scenario, the higher Local Bubble D/H ratio is actually a better estimate than (D/H)LDgfor the true local disk D/H, (D/H)LD. However, if (D/H)LDgis different from (D/H)LBgsimply because of variable astration and incomplete interstellar medium mixing, then (D/H)LD=(D/H)LDg.
ISM: Abundances - Stars: Individual: Alphanumeric: JL 9 - Stars: Individual: Alphanumeric: LS 1274 - Ultraviolet: ISM
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