Effect of Rapid Mass Accretion onto the Main-Sequence Stars

During the evolution of a close binary system, there is a phase with rapid mass exchange between its component stars. Effects of rapid mass inflow on the internal structure of the main-sequence stars are studied in this paper. The mass-receiving star becomes overluminous and its radius becomes larger. The latter result implies that only a part of the transferred matter is absorbed into the interior of the mass-receiving star and that the rest is accumulated just above the original surface of the star. When the rate of inflow is large, the radius becomes even comparable with that of a red giant star. When the inflow rate exceeds 60 percent of the critical accretion rate for the 20M star, its radius diverges. For a smaller-mass star (e.g., 0.75M ), the increase in the radius is much more appreciable and it reaches as much as 10 times the initial radius, even when the inflow rate exceeds about 0.1 percent of the critical value. Such rates of mass exchange have been frequently encountered by many authors. In such cases, the radius of the mass-receiving star will exceed its Roche limit, and mass and angular momentum will be lost from the binary system. Key words: Close binary; Eddington limit; Internal structure; Mass accretion.