Close Binaries Before and After Mass Exchange: A Comparison of Observations through Theoretical Computations

Extract

From a search through the literature 174 close binaries with completely known absolute dimensions are sampled. Distinction is made between systems before and after mass exchange, giving resp. 100 and 40 systems (a third group contains the systems not definitely belonging to these two). Mass, period and mass ratio distributions and relations of the group of “unevolved” binaries (i.e. prior to mass exchange) are transformed into corresponding distributions and relations of evolved binaries. The transformations are based upon the M_{1 f} = g (M_{1 i}) relation derived from an extended set of published theoretical computations on the evolution of close binaries. Final masses resulting from the same initial mass are averaged. Equations are derived for the cases A (for all masses), B1 (M_{1 i}/M_o < 2.8), B2 (2.8 < M_{1 i}/M_o < 9) and B3 (M_{1 i}/M_o > 9). For the changes of the period due to angular momentum loss the formalism of Vanbeveren et al. (1979) was adopted. The following characteristics of the system after mass exchange are computed: M_{1 f}, M_{2 f} (and q_f), P_f. Three different modes were applied for the mass loss from the system:

a) conservative case (mass and angular momentum of the system remain constant), called C.

b) non conservative case with 50% of the transferred mass leaving the system with a small or a large angular momentum loss (resp. called NC51 and NC53).

c) non conservative case with 100% of the transferred mass leaving the system with a small or a large angular momentum loss (resp. called NC101 and NC103).