Evolution of close binaries and origin of Algol-type systems

Abstract

The evolution of close binary systems was followed for ten systems with the initial mass of the primary in the range 1–4M _⊙ and with different initial mass ratios and initial separations. A brief discussion of the evolution of the contact component is presented for two separate cases: when the primary reaches its Roche lobe during central hydrogen burning (case A) and after the exhaustion of hydrogen in the center (case B).

The models obtained are compared with observed semi-detached systems separately for massive (with total mass greater than 5M _⊙) and low mass (with total mass below 4M _⊙) binaries. It is shown that the contact components of the observed massive binaries are probably burning hydrogen in the core. On the contrary, the majority of contact components of the observed low-mass binaries are burning hydrogen in the shell. The observed distribution of such binaries as a function of different luminosity excesses of contact components seems to indicate that their origin is connected with case A rather than with case B.