AAS 199th meeting, Washington, DC, January 2002
Session 65. FUSE Only
Display, Tuesday, January 8, 2002, 9:20am-6:30pm, Exhibit Hall

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[65.01] Illuminating Trends in ISM Elemental Abundances Revealed by STIS and FUSE Observations

S.I.B. Cartledge, D.M. Meyer, J.T. Lauroesch (Northwestern U.), U.J. Sofia (Whitman College)

We present HST STIS measurements of the interstellar O I, Mg II, P II, Mn II, Ni II, Cu II, Ge II, and Kr I absorption lines in over 40 sight lines with pathlengths of up to 5 kpc through the Galactic disk. Utilizing targeted and archival FUSE data, we have also obtained H2 measurements for over half of our sight lines. A trend toward lower gas-phase elemental abundance ratios with increasing mean total hydrogen sight line density (< nH > = N(H)/d) is evident for each element except krypton. Although such trends have previously been identified by Copernicus measurements, they are more distinct in our STIS/FUSE data which benefit from the improved measurement capabilities of these instruments. The case of oxygen in low density sight lines (< nH > less than 1 cm-3) is particularly intriguing. Although there is no trend with < nH > in this sample, shorter sight lines (d < 750 pc) have about 0.15 dex lower gas-phase oxygen abundances than for longer sight lines. In addition, we report the first sight line (HD152590) with an apparently solar Kr/H ratio. Since the inferred depletions for other elements in this sight line are characteristic of the cold ISM, the krypton enhancement appears to be a nucleosynthetic effect.

Financial support for this work was provided by the Space Telescope Science Institute through grants to Northwestern Univerisity and Whitman College.

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