Volume 410, Number 1, October IV 2003
|Page(s)||239 - 252|
|Section||Stellar structure and evolution|
|Published online||17 November 2003|
Delays in dwarf novae I: The case of SS Cygni
UMR 7550 du CNRS, Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: firstname.lastname@example.org
2 Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France e-mail: email@example.com
Corresponding author: M. R. Schreiber, firstname.lastname@example.org
Accepted: 25 July 2003
Using the disc instability model and a simple but physically reasonable model for the X-ray, extreme UV, UV and optical emission of dwarf novae we investigate the time lags observed between the rise to outburst at different wavelengths. We find that for “normal”, i.e. fast-rise outbursts, there is good agreement between the model and observations provided that the disc is truncated at a few white dwarf radii in quiescence, and that the viscosity parameter α is ~0.02 in quiescence and ~0.1 in outburst. In particular, the increased X-ray flux between the optical and EUV rise and at the end of an outburst, is a natural outcome of the model. We cannot explain, however, the EUV delay observed in anomalous outbursts because the disc instability model in its standard α-prescription form is unable to produce such outbursts. We also find that the UV delay is, contrary to common belief, slightly longer for inside-out than for outside-in outbursts, and that it is not a good indicator of the outburst type.
Key words: accretion, accretion discs / instabilities / stars: individual: SS Cygni / stars: novae, cataclysmic variables / stars: binaries : close
© ESO, 2003
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