Evolution of interacting binaries with a B type primary at birth

Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium e-mail: wvanrens@vub.ac.be; cdeloore@pandora.be; kijansen@vub.ac.be

Received: 31 May 2005
Accepted: 13 September 2005

Abstract

We revisited the analytical expression for the mass ratio distribution for non-evolved binaries with a B type primary. Selection effects governing the observations were taken into account in order to compare theory with observations. Theory was optimized so as to fit best with the observed q-distribution of SB1s and SB2s. The accuracy of this theoretical mass ratio distribution function is severely hindered by the uncertainties on the observations. We present a library of evolutionary computations for binaries with a B type primary at birth. Some liberal computations including loss of mass and angular momentum during binary evolution are added to an extensive grid of conservative calculations. Our computations are compared statistically to the observed distributions of orbital periods and mass ratios of Algols. Conservative Roche Lobe Over Flow (RLOF) reproduces the observed distribution of orbital periods but fails to explain the observed mass ratios in the range q ∈ 0.4–1. In order to obtain a better fit the binaries have to lose a significant amount of matter, without losing much angular momentum.