O VI in the local interstellar medium

We report the results of a search for Ovi absorption in the spectra of 80 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 approximately 35% of cases (where photospheric material is detected), the velocity differences between the interstellar and photospheric components were beneath the resolution of the FUSE spectrographs. Therefore, in 65% of these stars the interstellar and photospheric contributions could be separated and the nature of the Ovi component unambiguously determined. Furthermore, in other examples, where the spectra were of a high signal-to-noise, no photospheric material was found and any Ovi detected was assumed to be interstellar. Building on the earlier work of Oegerle et al. and Savage and Lehner, we have increased the number of detections of interstellar Ovi and, for the first time, compared their locations with both the soft X-ray background emission and new detailed maps of the distribution of neutral gas within the local interstellar medium. We find no strong evidence to support a spatial correlation between Ovi and SXRB emission. In all but a few cases, the interstellar Ovi was located at or beyond the boundaries of the local cavity. Hence, any T ∼ 300,000 K gas responsible for the Ovi absorption may reside at the interface between the cavity and surrounding medium or in that medium itself. Consequently, it appears that there is much less Ovi-bearing gas than previously stated within the inner rarefied regions of the local interstellar cavity.