Evolution of non-synchronized binary systems

A model for binary evolution is introduced which can determine whether the rotation of components is synchronized with the orbital motion, and can cal culate the evolution of both the synchronized and non-synchronized binary s ystems. With this model, the evolution of a binary system consisting of a 9 M. star and a 6 M. star is studied with mass transfer Case B. The result s hows that the synchronization of the rotational and orbital periods can be reached when the binary system is a detached system and before the occurren ce of the first mass transfer. After the onset of the first mass transfer, the binary system becomes non-synchronized. The mass accepted component (th e secondary) rotates faster with a period much smaller than that of the orb ital motion.