Evolutionary computations of the early-type contact binary SV Centauri

Abstract

Evolutionary models of the early-type contact binary SV Centauri are recalculated with contact condition taken into account. Two types of the contact condition are employed in the contact phase. With the initial masses of 13.4 and 7.0M _⊙ for the component stars, the observed features such as the rate of mass transfer, the degree of contact, and the positions of both components in the H-R diagram can be reproduced. In agreement with the conclusion given in the previous paper (Nakamuraet al., 1978), this indicates that the binary system SV Cen is actually in the rapid phase of mass transfer preceding the reversal of the mass ratio.

In contrast to the steadily increasing character of the rate of mass transfer shown in the previous paper, however, the rate of mass transfer suddenly turns to decrease as soon as the system evolves into the contact phase. This decreasing character continues until the rate drops to a minimum. In such contact phase the radius of the primary component remains almost unchanged, the secondary component increases its radius slowly, and the degree of contact increases in a definite way. Except a slight difference in the degree of contact evaluated, the use of different expressions for the contact condition does not produce practically any appreciable difference in the results.