Calculations are presented for the evolution of a binary system containing a 1.5-solar-mass primary initially separated by 3 solar radii from a 0.5-solar-mass secondary with a very deep convective envelope. Accretion is treated in two extremes where stream effects are neglected or included spherically symmetrically in the surface boundary conditions of the accreting component. The onset and initial stages of mass transfer are described, the development of mass loss on a dynamic time scale is followed, and the manifestation of a Bath-type instability in the mass-loss rate is examined. The detailed behavior of the primary's interior during this instability is analyzed, and the evolution of the accreting secondary is traced with and without the inclusion of stream effects. The model system is discussed in terms of the origin of W UMa systems. It is concluded that most W UMa systems have always existed in the contact state and that the behavior of the model supports the theory of a fission origin for close binaries.
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R. F. Webbink (1977) studied this question.