On the mass transfer process in binary systems

The condition that the radius of one component of a binary star is equal to that of its Roche lobe has so far been used as a criterion for the occurre nce of mass transfer. However, this criterion is only approximate. It is in troduced for the simplification of the calculations from three-dimensions t o one-dimension. A modified criterion is introduced, which is more strict a nd can also be used in one-dimensional calculations. In order to study the effect of the modified criterion on the evolution of binary systems, we cal culate the evolution of a binary system consisting of a 9M. star and a 6M. star with mass transfer Case A and Case B. We find that the mass transfer p rocess starts earlier and lasts longer when the modified criterion is adopt ed. Thus, the modified criterion for the mass transfer process has an obvio us influence on the orbital period of the system, the masses and the intern al structure of the component stars.