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J. Dupuis (JHU), S. Vennes (ANU), T. Lanz (U. of Maryland & GSFC), P. Chayer (UVIC & JHU)
We present FUSE observations of the hot white dwarfs in the post-CE binaries BPM 6502, EUVEJ2013+400, and EUVEJ0720-317. The abundance pattern observed in these stars is possibly affected by accretion from the cool star companion. In order to better understand the effect of accretion on the atmospheric composition of these stars, we measure the abundances of C, N, O, Si, P, and Fe from lines detected in the FUSE spectra. We report the detection of CIII, OVI, PV, and SiIV in the spectra of EUVEJ2013+400 (Teff = 48,000K) and EUVEJ0720-317 (Teff = 53,000K). BPM~6502, a cooler DA (Teff = 21,000K), shows photospheric absorption lines of CIII, NII, SiIII, SiIV, and FeIII. We measure the following abundances in EUVEJ0720-317 and EUVEJ2013+400 respectively: log (C/H) = -6.0, -5.8; log (O/H) = -6.1, -5.6; log (Si/H) = -6.1, -6.5; log (P/H) = -7.0, -7.7. For BPM~6502, we measure log (C/H) = -6.2, log (N/H) = -6.6, log (Si/H) = -6.1, and log (Fe/H) = -7.5. It is remarkable that although the carbon abundance is quite similar in the three stars, we see a decrease in the silicon and phosphorus abundances with decreasing effective temperature (as predicted by the radiative levitation theory) and an increase in the oxygen abundance. The presence of iron in BPM~6502 is surprising since it should not be supported by radiative levitation and is a possible evidence of ongoing accretion. This research is funded by NASA grants NAG5-11717 and NAG5-6551.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.