The D/H Ratio toward PG 0038+199
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 HIRES. We employ curve-of-growth, apparent optical depth, and profile-fitting techniques to measure the column densities and limits of many other species (H2, Na I, C I, C II, C III, N I, N II, O I, Si II, P II, S III, Ar I, and Fe II), which allows us to determine related ratios such as D/O, D/N, and the H2 fraction. Our efforts are concentrated on measuring gas-phase D/H, which is key to understanding Galactic chemical evolution, and comparing it to predictions from big bang nucleosynthesis. We find column densities logN(HI)=20.41+/-0.08, logN(DI)=15.75+/-0.08, and logN(H2)=19.33+/-0.04, yielding a molecular hydrogen fraction of 0.14+/-0.02 (2 σ errors), with an excitation temperature of 143+/-5 K. The high H I column density implies that PG 0038+199 lies outside of the Local Bubble; we estimate its distance to be 297+164-104 pc (1 σ). [DI+HD]/[HI+2H2] toward PG 0038+199 is 1.91+0.52-0.42×10-5 (2 σ). 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.
This paper is dedicated in memory of Ervin J. Williger, father of the first author, who passed away on 2003 September 13. His enthusiastic support and encouragement were essential to its successful completion. Based on data from the Far Ultraviolet Spectroscopic Explorer and the W. M. Keck Observatory.- Publication:
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The Astrophysical Journal
- Pub Date:
- May 2005
- DOI:
- 10.1086/429315
- arXiv:
- arXiv:astro-ph/0501320
- Bibcode:
- 2005ApJ...625..210W
- Keywords:
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- ISM: Abundances;
- ISM: Evolution;
- Ultraviolet: ISM;
- Stars: White Dwarfs;
- Astrophysics
- E-Print:
- 59 pages, 7 tables, 18 figures (1 standalone), accepted by ApJ v2 minor typos corrected