An analysis of active close binaries (CB) based on photometric measurements

This is the first in a series of papers devoted to the actual problematics in the determination of orbital and physical parameters of active CB on the basis of the interpretation of photometric observations. One solves the problem in two stages: by obtaining a synthetic light curve in the case when the parameters of the corresponding CB model are givena priori (direct problem) and by determining the parameters of the given model for which the best fit between the synthetic light curve and the observations is achieved (inverse problem (see Djura?evi?, 1991). In the first article of the series one presents the basis of the model developed for the synthesis of asymmetric, deformed, light curves of active CB with spots on their components. The modelling of the CB systems is based on the principles orginated in the Wilson and Devinney (1971; hereafter referred to as WD) model for the synthesis of a light curve generalised to include also the case of a nonsynchronous rotation of the components. The shapes of the components correspond to the equipotentials in the Roche model so that the critical Roche limits can be filled up to an arbitrary degree. In a spherical-coordinate system the surfaces of the components are divided into a large number of elementary cells whose intensity and angular radiation distribution are determined by the star temperature. limb darkening, gravitational darkening, and by the effect of reflection in the system. The active regions are approximated with circular spots. The presence of spots (dark or hot) enables to explain the asymmetry and depressions on the light curves of active CB. The model enables to be also interpreted the light curves of classic CB (without spots).