The OVI Issue
Résumé
We report the results of a search for O VI absorption in the spectra of ~100 hot DA white dwarfs observed by the FUSE satellite. We have carried out a detailed analysis of the radial velocities of interstellar and (where present) stellar absorption lines for the entire sample of stars. In many cases, the velocity differences between the interstellar and photospheric components are below the resolution of the FUSE spectrographs. However, in a significant number of cases the interstellar and photospheric contributions can be separated. Within this group, for those stars where O VI is positively detected, it is possible to unambiguously determine the nature of the O VI component (interstellar or photospheric). In the majority of stars where we find O VI absorption lines, the material is clearly associated with the stellar photosphere and not the interstellar medium. There are a number of lines-of-sight where the gas is interstellar in nature. Mostly these stars are located beyond the boundaries of the local cavity or are at high galactic latitude. Hence, it appears that the Local Bubble contains little hot gas. That component responsible for the O VI absorption may reside at the interface between the cavity and surrounding medium or in that medium itself and is also associated with the soft X-ray background