Far Ultraviolet Spectroscopic ExplorerSurvey of the Local Interstellar Medium within 200 Parsecs

We present FUSE observations of the interstellar gas toward 30 white dwarfand 1 subdwarf (SdO) stars. These sightlines probe the Local Bubble (LB) andthe local interstellar medium (LISM) near the LB. Our survey detected onlydiffuse H_2 molecular clouds along six sightlines. There is no evidence fromthis study that H_2 exists well inside the perimeter of the LB. The kinematicaltemperature for H_2 is less than the usual temperature observed in the localinterstellar clouds, implying different gas phases in the LISM. The relativeabundance ratios of Si II, P II, and Fe II give insight about the dust content.These ratios vary, but are similar to the depletion patterns observed in warmand halo diffuse clouds in more distant sightlines in the Galaxy. The N I/O Iand Ar I/O I ratios are significantly subsolar within the LB. Outside the LB alarger scatter is observed from subsolar to solar. Because Ar and N are onlyweakly depleted into dust grains if at all, the deficiencies of their neutralforms are likely due to photoionization. The evidence for significantionization of N (and hence Ar) is strengthened by the detection and measurementof N II, which is a dominant ion for this element toward many sightlines. Theseobservations imply that photoionization is the main ionization mechanism in theLISM and do not support the existence of a highly ionized condition in thepast. In view of the variations observed in the different atomic and ionicratios, the photoionization conditions vary significantly in the LB and theLISM. [Abridged.]Comment: Accepted for publication in the Ap