The Abundance of Interstellar Fluorine and Its Implications

We report results from a survey of neutral fluorine (F I) in the interstellar medium. Data from the Far Ultraviolet Spectroscopic Explorer (FUSE) were used to analyze 26 lines of sight lying both in the galactic disk and halo, including lines to Wolf-Rayet stars and through known supernova remnants. The equivalent widths of fluorine resonance lines at 951.871 A and 954.827 A were measured or assigned upper limits and combined with a nitrogen curve of growth to obtain F I column densities. These column densities were then used to calculate fluorine depletions. Comparisons are made to the previous study of F I by Federman et al. (2005) and implications for F I formation and depletion are discussed.Comment: 32 pages, 10 figures, Accepted to Ap

Molecular Hydrogen in the FUSE Translucent Lines of Sight: The Full Sample

We report total abundances and related parameters for the full sample of the FUSE survey of molecular hydrogen in 38 translucent lines of sight. New results are presented for the "second half" of the survey involving 15 lines of sight to supplement data for the first 23 lines of sight already published. We assess the correlations between molecular hydrogen and various extinction parameters in the full sample, which covers a broader range of conditions than the initial sample. In particular, we are now able to confirm that many, but not all, lines of sight with shallow far-UV extinction curves and large values of the total-to-selective extinction ratio, $R_V$ = $A_V$ / $E(B-V)$ -- characteristic of larger than average dust grains -- are associated with particularly low hydrogen molecular fractions ($f_{\rm H2}$). In the lines of sight with large $R_V$, there is in fact a wide range in molecular fractions, despite the expectation that the larger grains should lead to less H$_2$ formation. However, we see specific evidence that the molecular fractions in this sub-sample are inversely related to the estimated strength of the UV radiation field and thus the latter factor is more important in this regime. We have provided an update to previous values of the gas-to-dust ratio, $N$(H$_{\rm tot}$)/$E(B-V)$, based on direct measurements of $N$(H$_2$) and $N$(H I). Although our value is nearly identical to that found with Copernicus data, it extends the relationship by a factor of 2 in reddening. Finally, as the new lines of sight generally show low to moderate molecular fractions, we still find little evidence for single monolithic "translucent clouds" with $f_{\rm H2}$ $\sim$ 1.Comment: 35 pages, 5 tables, 7 figures, accepted for publication in The Astrophysical Journal Supplements Serie

A New FUSE Survey of Interstellar HD

We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with a wide range of extinctions. This follow up to an earlier survey was made to further assess the utility of HD as a cosmological probe; to analyze the HD formation process; and to see what trends with other interstellar properties were present in the data. We employed the curve-of-growth method, supported by line profile fitting, to derive accurate column densities of HD. We find that the N(HD)/2N(H2) ratio is substantially lower than the atomic D/H ratio and conclude that the molecular ratio has no bearing on cosmology, because local processes are responsible for the formation of HD. Based on correlations with E(B-V), H2, CO, and iron depletion, we find that HD is formed in the densest portion of the clouds; the slope of the logN(HD)/log(H2) correlation is greater than 1.0, caused by the destruction rate of HD declining more slowly than that of H2; and, as a sidelight, that the depletions are density dependent.Comment: 30 pages, 13 figures; Accepted for publication in Ap

An ultraviolet search for interstellar CS

High- and medium-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) and the Goddard High Resolution Spectrograph (GHRS) were used to study the diatomic molecule CS through the C-X(0,0) band at 1401 \uc5. The band was modeled to verify profile shape. The rest wavelength of the C-X band is refined to a value of 1400.88 \uc5 and a 3σ lower limit is set on the oscillator strength at 0.14 based on equivalent width upper limits of the A-X(0,0) CS Band at 2577 \uc5. The strength of the 1401 \uc5 band is compared to other interstellar parameters and implications for CS formation and destruction are briefly discussed

An ultraviolet search for interstellar CS

High- and medium-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) and the Goddard High Resolution Spectrograph (GHRS) were used to study the diatomic molecule CS through the C-X(0,0) band at 1401 \uc5. The band was modeled to verify profile shape. The rest wavelength of the C-X band is refined to a value of 1400.88 \uc5 and a 3σ lower limit is set on the oscillator strength at 0.14 based on equivalent width upper limits of the A-X(0,0) CS Band at 2577 \uc5. The strength of the 1401 \uc5 band is compared to other interstellar parameters and implications for CS formation and destruction are briefly discussed