A Survey ofO vi A bsorption in the LocalInterstellar M edium W illiam

W e report the results ofa survey ofO vi 1032 absorption along the lines ofsight to 25 white dwarfs in the localinterstellar m edium (LISM ) obtained with theFarUltravioletSpectroscopicExplorer(FUSE).W e nd thatinterstellar O viabsorption along allsightlinesisgenerally weak,and in a num berofcases, com pletely absent. No O viabsorption was detected with signi cance greater than 2 for12 ofthe25 stars,wherethe1 uncertainty is 4 m A,equivalent to an O vicolum n density of 3 10 cm 2 . Ofthe rem aining stars,m ost havecolum n densitiesN(O vi)< 10 cm 2 and no colum n densitiesexceed 1:7 10 cm 2 . For lines ofsight to hot (Te > 40;000 K) white dwarfs,there is som eevidencethattheO viabsorption m ay beatleastpartially photosphericor circum stellarin origin.W einterpretthe\patchy"distribution ofO viabsorption in term sofa m odelwhereO viisform ed in evaporativeinterfacesbetween cool cloudsand the hot,di use gasin the LocalBubble (LB).Ifthe cloudscontain tangled ortangentialm agnetic elds,then therm alconduction willbequenched overm ostofthe cloud surface,and O viwillbe form ed only in local\patches" where conduction isallowed to operate. W e nd an average O vispace density in the LISM of2:4 10 8 cm 3 ,which issim ilarto,orslightly largerthan,the valuein theGalacticdisk overkpcscales.Thislocaldensity im pliesan average O vicolum n density of 7 10 cm 2 over a path length of100 pc within