Close Binary Stars. I: Simple Models

The paper analyzes observations of close binary systems (CBSs), their radial velocity curves, and light curves. Various methods are described for fitting the light curve of eclipsing systems that consist of two spherical stars in a circular or elliptical orbit, as well as methods for considering the third light and the influence of a third body on the times of minima, and rectifying the light curves of eclipsing systems. The rotation of the apsidal line in a CBS is considered, as well as its use for determining the concentration of matter in the star's body. Possible mechanisms for variation in the orbital eccentricity in CBSs, the causes of variation in their orbital periods, and the effects of the mutual proximity of the components are discussed.