Cristina M. Oliveira

Overview of the Far Ultraviolet Spectroscopic Explorer Mission

The Far Ultraviolet Spectroscopic Explorer satellite observes light in the far-ultraviolet spectral region, 905-1187 Angstrom, with a high spectral resolution. The instrument consists of four co-aligned prime-focus telescopes and Rowland spectrographs with microchannel plate detectors. Two of the telescope channels use Al :LiF coatings for optimum reflectivity between approximately 1000 and 1187 Angstrom, and the other two channels use SiC coatings for optimized throughput between 905 and 1105 Angstrom. The gratings are holographically ruled to correct largely for astigmatism and to minimize scattered light. The microchannel plate detectors have KBr photocathodes and use photon counting to achieve good quantum efficiency with low background signal. The sensitivity is sufficient to examine reddened lines of sight within the Milky Way and also sufficient to use as active galactic nuclei and QSOs for absorption-line studies of both Milky Way and extragalactic gas clouds. This spectral region contains a number of key scientific diagnostics, including O VI, H I, D I, and the strong electronic transitions of H-2 and HD.

What Is the Total Deuterium Abundance in the Local Galactic Disk

Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, together with spectra from the Copernicus and interstellar medium absorption profile spectrograph (IMAPS) instruments, reveal an unexplained, very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond the Local Bubble. We argue that spatial variations in the depletion of deuterium onto dust grains can explain these local variations in the observed gas-phase D/H ratios. We present a variable deuterium depletion model that naturally explains the constant measured values of D/H inside the Local Bubble, the wide range of gas-phase D/H ratios observed in the intermediate regime [log N(H ) = 19.2-20.7], and the low gas-phase D/H ratios observed at larger hydrogen column densities. We consider empirical tests of the deuterium depletion hypothesis: (1) correlations of gas-phase D/H ratios with depletions of the refractory metals iron and silicon, and (2) correlation with the H2 rotational temperature. Both of these tests are consistent with deuterium depletion from the gas phase in cold, not recently shocked regions of the ISM, and high gas-phase D/H ratios in gas that has been shocked or otherwise heated recently. We argue that the most representative value for the total (gas plus dust) D/H ratio within 1 kpc of the Sun is ≥23.1 ± 2.4(1 σ) parts per million (ppm). This ratio constrains Galactic chemical evolution models to have a very small deuterium astration factor, the ratio of primordial to total (D/H) ratio in the local region of the Galactic disk, which we estimate to be fd ≤ 1.19(1 σ) or ≤1.12 ± 0.14(1 σ) depending on the adopted light-element nuclear reaction rates.

Abundances of Deuterium, Nitrogen, and Oxygen in the Local Interstellar Medium: Overview of First Results from the FUSE Mission

Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D i ,N i, and O i along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 to 179 pc. Five of the sight lines are within the Local Bubble, and two penetrate the surrounding H i wall. Reliable values of N(H i) were determined for five of the sight lines from Hubble Space Telescope (HST) data, International Ultraviolet Explorer (IUE) data, and published Extreme Ultraviolet Explorer (EUVE) measurements. The weighted mean of D i/H i for these five sight lines is ð1:52 � 0:08 Þ� 10 � 5 (1 � uncertainty in the mean). It is likely that the D i/H i ratio in the Local Bubble has a single value. The D i/O i ratio for the five sight lines within the Local Bubble is ð3:76 � 0:20 Þ� 10 � 2 .I t is likely that O i column densities can serve as a proxy for H i in the Local Bubble. The weighted mean for O i/H i for the seven FUSE sight lines is ð3:03 � 0:21 Þ� 10 � 4 , comparable to the weighted mean ð3:43 � 0:15 Þ� 10 � 4 reported for 13 sight lines probing larger distances and higher column densities. The FUSE weighted mean of N i/H i for five sight lines is half that reported by Meyer and colleagues for seven sight lines with larger distances and higher column densities. This result combined with the variability of O i/N i (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O i ,N i cannot be used as a proxy for H i or as a metallicity indicator in the LISM. Subject headings: cosmology: observations — Galaxy: abundances — ISM: abundances — ISM: evolution — ultraviolet: ISM

OXYGEN GAS-PHASE ABUNDANCE REVISITED

We present new measurements of the interstellar gas-phase oxygen abundance along the sight lines toward 19 early-type Galactic stars at an average distance of 2.6 kpc. We derive O i column densities from Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) observations of the weak 1355 Ainter- system transition. We derive total hydrogen column densities (NðH i Þþ 2NðH2Þ) using HST/STIS observa- tions of Lyand Far Ultraviolet Spectroscopic Explorer (FUSE) observations of molecular hydrogen. The molecular hydrogen content of these sight lines ranges from f ðH2 Þ¼ 2NðH2Þ=½NðH i Þþ 2NðH2Þ� ¼ 0:03 to 0.47. The average hHtot=EBV i of 6:3 � 10 21 cm � 2 mag � 1 with a standard deviation of 15% is consistent with previous surveys. The mean oxygen abundance along these sight lines, which probe a wide range of Galactic environments in the distant interstellar medium, is 10 6 (O/H)gas¼ 408 � 13 (1 � in the mean). We see no evi- dence for decreasing gas-phase oxygen abundance with increasing molecular hydrogen fraction, and the rela- tive constancy of (O/H)gas suggests that the component of dust containing the oxygen is not readily destroyed. We estimate that, if 60% of the dust grains are resilient against destruction by shocks, the distant interstellar total oxygen abundance can be reconciliated with the solar value derived from the most recent measurements of 10 6 (O/H)gas� ¼ 517 � 58 (1 � ). We note that the smaller oxygen abundances derived for the interstellar gas within 500 pc or from nearby B star surveys are consistent with a local elemental deficit. Subject headings: dust, extinction — ISM: abundances — ultraviolet: ISM

Interstellar Deuterium, Nitrogen, and Oxygen Abundances toward GD 246, WD 2331–475, HZ 21, and Lanning 23: Results from the FUSE Mission*

The interstellar abundances of D i ,N i, and O i in the local ISM are studied using high-resolution spectra of four hot white dwarfs. The spectra of GD 246, WD 2331� 475, HZ 21, and Lan 23 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) in the wavelength range 905–1187 A ˚ . The line of sight to GD 246 probes the Local Interstellar Cloud and at least one other H i cloud inside the Local Bubble, which contains most of the gas seen along this line of sight. The column densities of Hi ,C ii*, Sii, and Siii are measured using archival Hubble Space Telescope STIS echelle-mode observations. The H i column density is deter... . .. . .. . .. . .. ... ...

High-resolution FUSE and HST ultraviolet spectroscopy of the white dwarf central star of Sh 2-216

Context. We perform a comprehensive spectral analysis of LS V +46°21  in order to compare its photospheric properties to theoretical predictions from stellar evolution theory as well as from diffusion calculations. Aims. LS V +46°21 is the DAO-type central star of the planetary nebula Sh 2-216. High-resolution, high- S/N ultraviolet observations obtained with FUSE and STIS aboard the HST as well as the optical spectrum have been analyzed in order to determine the photospheric parameters and the spectroscopic distance. Methods. We performed a detailed spectral analysis of the ultraviolet and optical spectrum by means of state-of-the-art NLTE model-atmosphere techniques. Results. From the N IV – N V, O IV – O VI, Si IV – Si V, and Fe V – Fe VII ionization equilibria, we determined an effective temperature of

Abundances of Deuterium, Nitrogen, and Oxygen toward HZ 43A: Results from the FUSE Mission

(95\pm 2)\,{\rm kK}

Velocity Dispersion of the High Rotational Levels of H2

with high precision. The surface gravity is

Deuterium and Oxygen toward Feige 110: Results from the FUSE Mission

\log g~=~6.9\pm 0.2

O/H in the local bubble

. An unexplained discrepancy appears between the spectroscopic distance