AAS 195th Meeting, January 2000
Session 53. ISM: Ionized Gas
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

## [53.03] UV Absorption by Intermediate and High Velocity Galactic Gas toward PG0953+415

D. Fabian, B. D. Savage (U. Wisconsin - Madison), T. M. Tripp (Princeton U.)

We present an analysis of the ultraviolet interstellar absorption lines seen with the STIS E140M grating at a spectral resolution of R~40,000 toward the quasar PG0953+415 (z=0.239, l=179\arcdeg.79, b=+51\arcdeg.71). This diffuse galactic halo sightline shows absorption due to zero velocity gas, two intermediate velocity clouds at VLSR=-75, +52 km~s-1, and two high velocity clouds at VLSR=-150, +125 km~s-1. A deep \ion{H}{1} observation of this sightline with the Green Bank 140' indicates the presence of the intermediate velocity cloud IV16 at ~-75 km~s-1, and a broad emission component covering the velocity range +75 km~s-1 to +130 km~s-1. IV16 is detected in \ion{Al}{2}, \ion{S}{2}, \ion{Fe}{2}, and \ion{Si}{2} and we derive abundances from component fitting to those features. The positive velocity gas is highly ionized (\ion{Si}{3}/\ion{Si}{2} ~3) and seen in two distinct components in \ion{C}{2}, \ion{Si}{2}, and \ion{Si}{3}. \ion{C}{4} shows a broad absorption trough through those velocities. We also report the presence of a strong metal line absorption component at -150 km~s-1 that is not seen in \ion{H}{1} emission down to a detection limit of 8\times1017 cm-2. Complex A (~10\arcdeg away) is the only gas in the vicinity at the proper velocity. This component is also highly ionized (\ion{Si}{3}/\ion{Si}{2} ~1) and is seen in the strong neutral gas lines but not at all in the high ion species. We discuss the physical and chemical properties of these objects in the context of other HVC studies.

We appreciate NASA support for this research through grant GO-06499.02 from STScI.

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