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A.P. Linnell, P. Szkody (U.Wash.)
V1159~Ori belongs to the subgroup of four dwarf novae with very short supercycles. Important characteristics are: orbital period, 89.54 min.; mean interval between outbursts, 3.75d; supercycle, 45d; no eclipses. We have used the BINSYN program suite to fit synthetic system spectra to IUE spectra for two normal outbursts, a superoutburst, and a quiescent state. It is not possible to fit the outburst spectra with a standard model stationary accretion disk (i.e.,T(R)=T*(R/R*)-0.75). By adopting flatter temperature profiles we achieved accurate fits to outburst spectra over a spectral range of 1800Å. The outer part of the outburst accretion disk is hotter than on the stationary model. There is no evidence for a boundary layer. A putative rim bright spot would be overwhelmed by the accretion disk luminosity during outburst.
Disk instability models presume that, during quiescence, accretion disk mass accumulates at a T\rm eff less than about 6000K. For this condition, the white dwarf and rim bright spot would dominate the FUV system light. BINSYN showed that no model with these characteristics could fit the observed IUE flux level of 35% of outburst maximum. The observations demand a radiating area large enough that only the accretion disk face can provide it. It is believed that much of the quiescent accretion disk is optically thin and that the standard model would not be applicable. Nevertheless, by adopting a reduced rate of mass transfer and a standard model we were able to produce a fairly good fit to the observed IUE spectrum at quiescence. Interestingly, in this model roughly the inner half of the accretion disk remained above the high viscosity state transition temperature. Evidence for a hot quiescent boundary temperature is absent. As a check, we used BINSYN to calculate the relative system V luminosity at normal outburst and during quiescence. The calculated outburst amplitude is in reasonable accord with observation. Tha data are consistent with outside-in outbursts, in accord with theory for high \dot{M} systems, but with a cooling wave that does not reach the inner disk region.
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