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B.D. Savage (U.W. Madison), K.R. Sembach (JHU), E.B. Jenkins (Princeton), J.M. Shull (U. Colorado), D.G. York (U. Chicago), G. Sonneborn (NASA/GSFC), H.W. Moos, S.D. Friedman, W.R. Oegerle, J.D. Kruk (JHU), FUSE Science Team
Far Ultraviolet Spectroscopic Explorer observations of stars in the Magellanic Clouds, AGNs, and QSOs are analyzed to obtain information about O VI 1031.93 and 1037.62 Å\ absorption occurring over long paths through the Milky Way halo. With 113.87 eV required to ionize O V, O VI is the best diagnostic of the hot interstellar medium at wavelengths > 912 Å. O VI peaks in abundance at T ~ 3 \times105 K for gas in collisional ionization equilibrium and is an excellent tracer of cooling hot gas. The FUSE observations were obtained prior to telescope focusing and have spectral resolutions of ~ 15,000, or 20 km /sec. The AGNs and QSOs studied include ESO141-055, H1821+643, VIIZw118, PG0804+761, PG0052+251, Mrk876, and several others scheduled for November and December 1999. The O VI line at 1037.62 Å\ is often blended with absorption from C II* and the H2 (5,0) R(1) and P(1) lines. However, the O VI 1031.93 Å\ line is usually free of blending. Since the O VI 1031.93 Å\ halo gas absorption is relatively broad compared to the instrumental resolution, the measurements provide reliable information about the O VI column density and the kinematics of the gas. The FUSE observations are combined with earlier O VI results from the Copernicus Satellite and from ORFEUS to obtain measures of the general distribution of O VI in the halo of the Galaxy, the scale height of O VI, the degree of irregularity in the distribution of hot halo gas, and the relationships between O VI and other highly ionized species including Si IV, C IV, and N V. This work is supported by NASA contract NAS5-32985.