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C. Miskey (CUA/IACS/GSFC), F. Bruhweiler (CUA/IACS), J. Gabel (CUA/IACS/GSFC), W. Feibelman (NASA/GSFC), J. Holberg (LPL/Arizona), M. Barstow (Leichester)
We present preliminary results for observations obtained by the Far-Ultraviolet Spectral Explorer (FUSE) of three Wolf-Rayet pre-white dwarfs, the nuclei of NGC 6905, NGC 5189, and NGC 5315. These stars represent some of the hottest objects (Teff ~ 100-170k K) in the H-R diagram. All three stars display ultra-high ionization emission lines, most notably emission from hydrogen-like O V III at UV and optical wavelengths. Previous results indicate this emission is superposed upon lower ionization, slightly shortward-shifted absorption features that may arise from the base of a stellar wind. The absorption and emission clearly delineate two distinct regions of ionization. Time-tagged FUSE data can test whether the emission is localized to "hot spots" on the stellar surface. These data, for all three stars, reveal no apparent temporal variability over timescales comparable to the stellar rotation periods, which tends to rule out the hot spot model. Interstellar H I/Ly-beta and molecular hydrogen absorption complicates the analysis of the stellar O VI resonance doublet P Cygni profiles. Nonetheless, these O VI features show pronounced net emission overwhelming any shortward-shifted absorption. The O VI emission equivalent width is quite strong in the stars of NGC 5189 and 6905, but significantly weaker in NGC 5315. The emission complex at 1160-1185 A is largely dominated by C IV 1168 in NGC 5189 and NGC 6905. In NGC 5315, this emission complex appears to be almost entirely the P Cygni profile of the 3P-3P0 multiplet of C III 1175. Possible O VIII 1165 emission is seen in the FUSE bandpass only in the central star of NGC 6905. This is the star with the most pronounced UV and optical O VIII emission as well. Line identification and a comparsion of the FUSE and IUE spectra for these objects are also presented.