Other
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...439..957s&link_type=abstract
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 2, p. 957-962
Other
51
Absorption Spectra, Abundance, Carbon, Cataclysmic Variables, Lyman Alpha Radiation, Novae, Spectroscopy, White Dwarf Stars, Faint Object Camera, Hubble Space Telescope, Metallicity, Photosphere, Spectrum Analysis, Stellar Composition, Stellar Envelopes
Scientific paper
Two consecutive Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra of the exposed white dwarf in the ultrashort-period, high-amplitude, dwarf nova WZ Sge, reveal a rich absorption line spectrum of neutron carbon and ionized metals, the Stark-broadened Lyman-alpha absorption wing, the H2 quasi-molecular Lyman-alpha 'satellite' absorption line, and a double-peaked C IV emission line which is variable with orbital phase. A synthetic spectral analysis of the white dwarf yields Teff = 14,900 K +/- 250 K, log g = 8.0. In order to fit the strongest C I absorption lines and account for the weakness of the silicon absorption lines, the abundance of carbon in the photosphere must be approximately 0.5 solar, silicon abundance is 5 x 10-3 solar, with all other metal species appearing to be 0.1-0.001 times solar. The H2 quasi-molecular absorption is fitted very successfully. The photospheric metals have diffusion timescales of fractions of a year, and thus they must have been accreted long after the 1978 December outburst. The source of the most abundance metal, carbon, is considered. If the time-averaged accretion rate during quiescence is low enough for diffusive equilibrium to prevail, then the equilibrium accretion rate pf neutron carbon is 7 x 10-16 solar mass/yr. A convective dredge-up origin for the concentration of carbon is extremely unlikely, given that the white dwarf atmosphere is H-rich while in single degenerates showing carbon and hydrogen, the C and H are trace elements in a helium background. Additional implications are explored.
Cheng Fu-Hua
Gilliland Ron L.
Huang Min
Hubeny Ivan
Long Knox S.
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