Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two New Low Galactic D/H Measurements from FUSE   We analyze interstellar absorption observed towards two subdwarf O stars, JL
9 and LSS 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)e-5 towards JL 9, and D/H=(0.76+/-0.36)e-5 towards LSS
1274 (2 sigma uncertainties). With distances of 590+/-160 pc 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 log
N(H I)<19.2 suggest that the gas-phase D/H value within the Local Bubble is
(D/H)_LBg=(1.56+/-0.04)e-5. However, the four longest Galactic lines of sight
with measured D/H, which have d>500 pc and log N(H I)>20.5, suggest a
significantly lower value for the true local-disk gas-phase D/H value,
(D/H)_LDg=(0.85+/-0.09)e-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)_LDg for the true local-disk D/H, D/H)_LD. However, if (D/H)_LDg is
different from (D/H)_LBg simply because of variable astration and incomplete
ISM mixing, then (D/H)_LD=(D/H)_LDg.

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The categories of this paper are: acc-phys
1
The categories of this paper are: cs
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex