Light-curve synthesis for close binaries: An extended shock as an analog of a hot spot in cataclysmic variables

Abstract

Studies of the light curves of close binary systems (CBSs) at late stages of their evolution provide rich information about the structure of gas streams, flows, disks, and other formations associated with the flow of matter onto the relativistic object. Simple intuitive concepts about the matter-flow pattern in CBSs are often unable to fully explain the observed light curves, which sometimes display very complicated shapes. This is true both of cataclysmic binary systems (eruptive variables), with a red dwarf that fills its Roche lobe and overflows onto its companion through the inner Lagrangian point, and of white dwarfs surrounded by optically bright and geometrically thick accretion di sks. The orbital light curves of cataclysmic variables often display “humps”—recurrent increases of the brightness by up to ~1 m , usually at orbital phases ~0.7—0.9 (phase 0.0