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Paper: Kinematics, Ionization, and Abundances of the High Velocity Clouds Toward PG1116+215
Volume: 348, Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE
Page: 394
Authors: Ganguly, R.; Sembach, K.R.; Savage, B.D.; Tripp, T.M.
Abstract: We present ultraviolet spectra of the high Galactic latitude sight-line toward PG1116+215 from FUSE and HST/STIS. The high resolution (20 km/s for FUSE, 6.5 km/s for STIS) and broad wavelength coverage (905—2820 Å) allow us to examine the detailed kinematics, ionization, and abundances of the high velocity cloud (HVC) at vLSR = +184km s−1. We detect a wide range of ions, including H I, O I, and O VI. The fortuitous detection of both O I and H I in this isolated HVC allows for a robust, albeit uncertain, metallicity constraint of ∼0.2 solar for the neutral gas. From comparison of the O VI, Si II, and O I column densities, we estimate that ionized gas dominates neutral gas by at least 10:1. We suggest a scenario where clumps of gas, which produce low ions, are interacting with a low-density medium, such as the Galactic halo or corona, which produces the high ions in the interaction region. A simple photoionization model of the neutral and low ions implies densities of at least 2×10−3 cm−3 for the low ionization gas.
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