The Deuterium, Oxygen, and Nitrogen Abundance Toward LSE 44

We present measurements of the column densities of interstellar DI, OI, NI, and H2 made with FUSE, and of HI made with IUE toward the sdO star LSE 44, at a distance of 554+/-66 pc. This target is among the seven most distant Galactic sight lines for which these abundance ratios have been measured. The column densities were estimated by profile fitting and curve of growth analyses. We find D/H = (2.24 +1.39 -1.32)E-5, D/O = (1.99 +1.30 -0.67)E-2, D/N = (2.75 +1.19 -0.89)E-1, and O/H = (1.13 +0.96 -0.71)E-3 (2 sigma). Of the most distant Galactic sight lines for which the deuterium abundance has been measured LSE 44 is one of the few with D/H higher than the Local Bubble value, but D/O toward all these targets is below the Local Bubble value and more uniform than the D/H distribution. (Abstract abridged.)Comment: 20 pages, including 9 figures. Accepted for publication in Ap

Deuterium and Oxygen Toward Feige 110: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

We present measurements of the column densities of interstellar DI and OI made with the Far Ultraviolet Spectroscopic Explorer (FUSE), and of HI made with the International Ultraviolet Explorer (IUE) toward the sdOB star Feige 110 [(l,b) = (74.09, -59.07); d = 179 +265 -67 pc; z = -154 +57 -227 pc]. Our determination of the DI column density made use of curve of growth fitting and profile fitting analyses, while our OI column density determination used only curve of growth techniques. The HI column density was estimated by fitting the damping wings of the interstellar Ly alpha profile. We find log N(DI) = 15.47 +/- 0.06, log N(OI) = 16.73 +/- 0.10, and log N(HI) = 20.14 +0.13 -0.20 (all errors 2 sigma). This implies D/H = (2.14 +/- 0.82) x 10^-5, D/O = (5.50 +1.64 -1.33) x 10^-2, and O/H = (3.89 +/- 1.67) x 10^-4. Taken with the FUSE results reported in companion papers (Moos et al. 2001) and previous measurements of the local interstellar medium, this suggests the possibility of spatial variability in D/H for sight lines exceeding ~100 pc. This result may constrain models which characterize the mixing time and length scales of material in the local interstellar medium.Comment: 24 pages, 9 figures. Accepted for publication in the Astrophysical Journal Supplement Series. Replacement corrects a typo in original submissio

Neutron-induced nucleosynthesis

Neutron--induced nucleosynthesis plays an important role in astrophysical scenarios like in primordial nucleosynthesis in the early universe, in the s--process occurring in Red Giants, and in the $\alpha$--rich freeze--out and r--process taking place in supernovae of type II. A review of the three important aspects of neutron--induced nucleosynthesis is given: astrophysical background, experimental methods and theoretical models for determining reaction cross sections and reaction rates at thermonuclear energies. Three specific examples of neutron capture at thermal and thermonuclear energies are discussed in some detail.Comment: 40 pages (uses kluwer.sty), 2 postscript figures (uses psfig), accepted for publication in Surveys in Geophysics, uuencoded tex-files and postscript-files available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Geo.u