Issue |
A&A
Volume 410, Number 1, October IV 2003
|
|
---|---|---|
Page(s) | 239 - 252 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20031221 | |
Published online | 17 November 2003 |
Delays in dwarf novae I: The case of SS Cygni
1
UMR 7550 du CNRS, Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: hameury@astro.u-strasbg.fr
2
Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France e-mail: lasota@iap.fr
Corresponding author: M. R. Schreiber, mschrei@astro.u-strasbg.fr
Received:
27
May
2003
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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