Properties of O vi Absorption in the Local Interstellar Medium

We report on the properties of LISM O VI absorption observed with 20 km/sresolution FUSE observations of 39 white dwarfs (WDs) ranging in distance from37 to 230 pc with a median distance of 109 pc. LISM O VI is detected with>2sigma significance along 24 of 39 lines of sight. The column densities rangefrom log N(O VI) = 12.38 to 13.60 with a median value of 13.10. The line ofsight volume density, n(O VI) = N(O VI)/d exhibits a large dispersion rangingfrom (0.68 to 13.0)x10(-8) cm(-3) with an average value 3.6x10(-8) cm(-3) twicelarger than found for more distant sight lines in the Galactic disk. Thenarrowest profiles are consistent with thermal Doppler broadening of O VI nearits temperature of peak abundance, 2.8x10(5) K. Comparison of the averagevelocities of O VI and C II absorption reveals 10 cases where the O VIabsorption is closely aligned with the C II absorption as expected if the O VIis formed in a condensing interface between the cool and warm absorption and ahot exterior gas. The comparison also reveals 13 cases where O VI absorption isdisplaced to positive velocity by 7 to 29 km/s from the average velocity of CII. The positive velocity O VI appears to be tracing the evaporative flow of OVI from a young interface between warm gas and a hot exterior medium. However,it is possible the positive velocity O VI is instead tracing cooling hot LocalBubble (LB) gas. The properties of the O VI absorption in the LISM are broadlyconsistent with the expectations of the theory of conductive interfaces caughtin the old condensing phase and possibly in the young evaporative phase oftheir evolution.Comment: 64 pages and 12 figures. Accepted by the Astrophysical Journal Supplement, January 2006, v16