Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003apj...582..352w&link_type=abstract
The Astrophysical Journal, Volume 582, Issue 1, pp. 352-357.
Astronomy and Astrophysics
Astronomy
23
Accretion, Accretion Disks, Stars: Binaries: Close, Stars: Novae, Cataclysmic Variables, Stars: Individual: Constellation Name: Ww Ceti, Stars: Individual: Constellation Name: Em Cygni, Stars: Individual: Constellation Name: Cz Orionis, Stars: White Dwarfs
Scientific paper
We explore the origin of the far-UV (FUV) spectra of three dwarf novae using combined high-gravity photosphere and accretion disk models. We have carried out an IUE archival comparative study of the three U Gem-type dwarf novae EM Cyg, CZ Ori, and WW Cet. For EM Cyg, the FUV spectrum during quiescence is dominated by an accretion disk with M=5×10-11 Msolar yr-1 contributing 92% of the FUV light and a white dwarf with upper limit Teff<24,000 K contributing <~8% of the light. For CZ Ori, the accretion disk with M=3.5×10-10 Msolar yr-1 contributes 99% of the FUV light while the white dwarf has an upper limit Teff<21,000 K and contributes <~1% of the light. For WW Cet, we find that best-fitting disk models and disk plus white dwarf models yield a distance that appears far too large. A single-temperature white dwarf fit with Teff=22,000 K implies a distance of 150 pc. CZ Ori and EM Cyg are dominated by the accretion disk during quiescence but with accretion rates that differ by over a factor of 10. In the case of EM Cyg, which has a higher inclination, it is possible that the nearly edge-on aspect of the disk may hide a much hotter white dwarf. There are now 17 analyzed dwarf nova systems with Porb<120 mintues and 11 systems with Porb>180 m. The average Teff below the lower boundary of the period gap is Teff=15,547 K, while the average Teff above the upper boundary of the period gap is Teff=31,182 K. The Teff of the white dwarfs strengthens the overall conclusion that the white dwarfs in cataclysmic variables above the period gap appear to be a factor of 2 times hotter than the accreting white dwarfs in dwarf novae below the period gap.
Sion Edward M.
Winter Lisa
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