FUSE Observations of O 6 Absorption in the Local Interstellar Medium

Details FUSE Observations of O 6 Absorption in the Local Interstellar Medium FUSE Observations of O 6 Absorption in the Local Interstellar Medium

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...197.0718o&link_type=abstract

American Astronomical Society, 197th AAS Meeting, #07.18; Bulletin of the American Astronomical Society, Vol. 32, p.1404

Astronomy and Astrophysics

Astronomy

3

Scientific paper

We report the results of an initial FUSE survey of O 6 λ 1032 absorption along the lines of sight to eleven nearby white dwarfs, ten of which are within the Local Bubble (LB; d ⪉ 100 pc). A goal of this survey is to investigate the possible formation of 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 O 6 throughout the Galactic disk. We find no O 6 absorption toward two stars, and the column densities along three additional sight lines are quite low; N(O 6) ~ 5 x 1012 cm-2. In several directions, we observe rather broad, shallow absorption with N(O 6) ~ 1-2 x 1013 cm-2. Models of conductive interfaces predict narrow profiles with N(O 6) ⪆ 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 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 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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