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The Astrophysical Journal


We present FUSE observations of the hot white dwarfs in the post-common-envelope binaries Feige 24, EUVE J0720-317, BPM 6502, and EUVE J2013+400. The spectra show numerous photospheric absorption lines, which trace the white dwarf orbital motion. We report the detection of C III, O VI, P V, and Si IV in the spectra of Feige 24, EUVE J0720-317, and EUVE J2013+400 and the detection of C III, N II, Si III, Si IV, and Fe III in the spectra of BPM 6502. Abundance measurements support the possibility that white dwarfs in post-common-envelope binaries accrete material from the secondary star wind. The FUSE observations of BPM 6502 and EUVE J2013+400 cover a complete binary orbit. We used the FUSE spectra to measure the radial velocities traced by the white dwarf in the four binaries, where the zero-point velocities were fixed using the ISM velocities in the line of sight of the stellar systems. For BPM 6502 we determined a white dwarf velocity semiamplitude of KWD = 18.6 ± 0.5 km sˉ¹, and with the velocity semiamplitude of the red dwarf companion (KRD = 75.2 ± 3.1 km sˉ¹), we estimate the mass ratio to be q = 0.25 ± 0.01. Adopting a spectroscopic mass determination for the white dwarf, we infer a low secondary mass of M RD = 0.14 ± 0.01 M⊙. For EUVE J2013+400 we determine a white dwarf velocity semiamplitude of KWD = 36.7 ± 0.7 km sˉ¹. The FUSE observations of EUVE J0720-317 cover approximately 30% of the binary period and, combined with the HSTGHRS measurements, we update the binary properties. FUSE observations of Feige 24 cover approximately 60% of the orbit, and we combine this data set with HST STIS data to update the binary properties.



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