AAS 201st Meeting, January, 2003
Session 33. Stars Dead or Alive
Oral, Monday, January 6, 2003, 2:00-3:30pm, 606-607

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[33.01] Orbital Parameters of the Post-CE Binaries BPM 6502, EUVE 0720-317 and EUVE 2013+400

S. Vennes (ANU), J. Dupuis (JHU), A. Kawka (Murdoch)

We present FUSE observations of the hot white dwarfs in the post-CE binaries BPM~6502, EUVE~0720-317, and EUVE~2013+400. The spectra show numerous photospheric absorption lines which trace the white dwarf orbital motion. The FUSE observation of BPM~6502 covers a complete binary orbit. We used the ephemeris of Kawka et al. (2002, AJ, in press) to determine the orbital phase of velocity measurements extracted from \ion{C}{3}, \ion{Si}{3}, and \ion{Fe}{3} absorption lines, and we determined the white dwarf velocity semi-amplitude K1 = 18.6±.9 km s-1. Using the velocity semi-amplitude of the red dwarf measured by Kawka et al., K2 = 77± km s-1, we estimate the mass ratio q = M2/M1 = 0.242±.017. Adopting a spectroscopic mass determination for the white dwarf, we infer a low secondary mass of M2 = 0.12±.01. We discuss the implications of the discovery of a low-mass secondary for common-envelope theory. The FUSE observations of EUVE~0720-317 and EUVE~2013+400 cover approximately 0.3 binary phase and are primarily useful for abundance determinations (see abstract by Dupuis et al.), but we compare the new velocity measurements to the HST GHRS velocity measurements (Vennes et al. 1999, ApJ 523, 386). Abundance measurements in all three objects support the possibility that white dwarfs in post-CE binaries accrete material from the secondary star wind. This work is supported by NASA grants NAG5-11717 and NAG5-6551. S.V. is a QEII fellow of the ARC.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.