AAS 197, January 2001
Session 7. Gas in the Galactic ISM
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[7.18] FUSE Observations of \ion{O}{6} Absorption in the Local Interstellar Medium

W.R. Oegerle (JHU), E.B. Jenkins (Princeton), R.L. Shelton (JHU), D.V. Bowen (Princeton), FUSE Team

We report the results of an initial FUSE survey of \ion{O}{6} \lambda1032 absorption along the lines of sight to eleven nearby white dwarfs, ten of which are within the Local Bubble (LB; d \la 100 pc). A goal of this survey is to investigate the possible formation of \ion{O}{6} in the conductive interfaces between cool (~104 K) clouds immersed in the presumably hot (106 K) gas within the LB. This mechanism is often invoked to explain the widespread presence of \ion{O}{6} throughout the Galactic disk.

We find no \ion{O}{6} absorption toward two stars, and the column densities along three additional sight lines are quite low; N(\ion{O}{6}) ~5 \times 1012 cm-2. In several directions, we observe rather broad, shallow absorption with N(\ion{O}{6}) ~1-2 \times 1013 cm-2. Models of conductive interfaces predict narrow profiles with N(\ion{O}{6}) \ga 1013 cm-2 per interface (Slavin 1989, Borkowski et al 1990), in the absence of a significant transverse magnetic field. Hence, our observations of weak \ion{O}{6} absorption indicate that conduction is being quenched, possibly by non-radial magnetic fields.

Alternatively, the gas within the LB may not be hot. Breitschwerdt & Schmutzler (1994) have proposed a model for the LB in which an explosive event within a dense cloud created rapid expansion and adiabatic cooling, resulting in a cavity containing gas with a kinetic temperature of T~ 50,000 K, but with an ionization state characteristic of much hotter gas. This model has a number of attractive features, but appears to predict significantly more \ion{O}{6} than we observe.

This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U. S. participants has been provided by NASA contract NAS5-32985.

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