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Session 109 - Novae & Cataclysmic Variables.
Display session, Saturday, January 10
Exhibit Hall,

[109.12] Implications of the Photospheric Chemical Abundances of the White Dwarf in the Ultra-Short Period Dwarf Nova WZ Sagittae

R. Slevinsky, D. Stys, S. West, E. M. Sion, F. H. Cheng (Villanova U.), P. Szkody (U.WA)

We present chemical abundances obtained from Hubble Space Telescope Goddard High-Resolution Spectrograph G140L spectra, FOS G130H spectra, and IUE archival spectra of the white dwarf in WZ Sge, exposed during quiescence since the time of its 1978 December outburst. All spectra are dominated by strong, broadened photospheric C I absorption features centered at 1356 ÅÅ\ and 1464 Åand N I centered at 1494 ÅThe spectra also show the Stark-broadened Ly\alpha red absorption wing, H_2 quasi-molecular Ly\alpha ``satellite'' absorption lines, and Si IV \lambda\lambda1393,1402 absorption lines. Our best fitting synthetic spectra yielded a rapidly rotating white dwarf with velocity V_rot sin i =1,200^+300_-400 km s^-1 (Cheng et al. 1997, ApJL, 484, L149), white dwarf effective temperature T_wd = 14,800 K, the gravity log g = 8.0, the chemical abundances with 3\sigma error-bars, in number relative to solar, C, 5.0^+2.0_-2.0; N, 3.0^+1.0_-1.0; Si, <0.1; and all other metals, 0.01. Earlier FOS G130H spectra reported by Sion and coworkers reveal rotational velocity V_rot sin i = 1,100^+400_-400 km s^-1, T_wd = 14,800 K, the gravity log g = 8.1, the chemical abundances, C, 2.0^+5.0_-1.5; N, 1.0^+3.0_-1.0; Si, <0.1; and all other metals, 0.01. We present several possible interpretations of the chemical abundances including processed matter from the stripped core of the substellar secondary, accretion-diffusion during ongoing accretion, ordinary convective dredgeup and shear mixing dredgeup of metals from deeper layers during the tangential accretion process. This work is supported by Summer Undergraduate Research Grants from the NASA Delaware Space Grant Colleges Consortium, by NASA LTSA grant NAG-3221 and by GO-6085.01-95a from the Space Telescope Science Institute which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA Contract NAS5-26555.

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