Secular evolution of cataclysmic binaries - Evolution of the secondary and the period gap

During the evolution of low mass main-sequence stars subject to mass loss at constant rates, stars of progressively smaller mass become fully convective, and the behavior of convection along the computed sequences is a function of both the star's chemical stratification and the degree of departure from thermal equilibrium. Sequences computed with mass loss rates of 10 to the -10th, 10 to the -9th, and 5 x 10 to the -9th solar masses/year all show that, at some stage, the star begins to depart from thermal equilibrium and, due to the reaction of the convective envelope to mass loss, its radius becomes larger than that corresponding to thermal equilibrium for the same total mass and chemical stratification. Information derived from the numerical computation of the thermal time scales of some of these structures, switching the mass loss on and off and studying the readjustment of the structure, is applied to the interpretation of the secular evolution of cataclysmic binaries.