A MODEL OF LIGHT-CURVE SYNTHESIZING FOR DWARF NOVAE AND THE ANALYSIS OF THE OY CAR OBSERVATIONS BY APPLICATION OF THE INVERSE-PROBLEM METHOD

The paper contains a model synthesizing the light curves of novae and novae-like stars, as well as of active close binaries (CB) in the phas e of an intensive matter exchange between the components with accretio n onto a white dwarf. The model considers the radial and azimuthal tem perature distributions in the disk enabling a successful interpretatio n of asymmetrically deformed light curves characteristic for these sys tems. The analysis of the observed light curves is performed by using the inverse-problem method (Djurasevic, 1992b) adapted to this model. In the particular case the parameters for the dwarf-nova OY Car are es timated on the basis of the U and B observations (Wood et al., 1989). The synthetic light curves obtained through the inverse-problem solvin g, as a whole, fit the observations well which indicates that it is po ssible to estimate the system parameters on the basis of the model pro posed here. The obtained results indicate a complex hot-spot structure approximated in the model with two components - a central part and a surrounding spot larger in size. The central hot-spot part (temperatur e about 10000 K is surrounded asymmetrically by the larger spot lower in temperature (about 7000 K). The radiation of the central hot spot i s 'beamed' forward by about 20 degrees. The angular size of the hot-sp ot central part is about 5 degrees, the centre longitude is 322 degree s, whereas for the surrounding spot the size is about 33 degrees and t he longitude of the centre about 300 degrees. For the mass ratio of th e components q = 0.102 one finds for the orbit inclination about 83 de grees.8. The analysis shows that the disk radius is about 51% of the c orresponding Roche lobe radius. Based on the U and B light curves the quiescent disk-edge temperature is estimated to about 5500 K (U), i.e. 4400 K (B). The disk-radial-temperature profile is much flatter than in the steady-state-approximation case. Beginning from the edge toward s the disk centre the temperature slowly increases attaining about 720 0 K (U), i.e. 5700 K (B) near the white dwarf. The differences in the solutions for the U and B light curves can be due to deviations in the disk radiation from the blackbody approximation assumed in the presen t model. Expressed in the units of the distance between the component centres [D = 1] the disk size is estimated to about 0.304 [D = 1], its thickness to 0.014 [D = 1], and the white-dwarf radius to about 0.02 [D = 1]. The white-dwarf temperature is about 15 000 K. The obtained r esults are in a relatively good agreement with the system parameters e stimated earlier (Wood et al., 1989). This indicates that the proposed model of the system and the corresponding inverse-problem method brie fly presented here are fully applicable to the analysis of active CB l ight curves in this evolutionary phase. Though the model given here in cludes a number of approximations, it enables an independent procedure in the observational-material analysis based on the light-curve synth esis and on the application of the inverse-problem method. Results obt ained by applying such an independent method can also serve as a reaso nable way in testing the solutions obtained by utilising the earlier a pproaches.