Evolution of binaries with a B-type primary

Algols are relatively numerous, easy to observe and in a stable evolutionary stage. They therefore supply reliable observed orbital periods and – to a lesser extent – mass ratios. These observations are used to test the evolution of interacting binaries with an initial B type primary. We examine the question if – yes or no – mass can be lost from the system during Roche Lobe Overflow (RLOF). Starting with the characteristics of unevolved binaries with a B-type primary we first compare the observed distributions of orbital periods and mass ratios of Algols with the statistics obtained from conservative evolution. Conservative 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 binaries have to lose a significant amount of matter, without losing much angular momentum. We present a scenario of this event through the combined action of spin-up and accreted radiation pressure during a short pre-Algol phase of RLOF.