Our binary evolutionary code predicted until now the position of both stars in the HRD, the characteristics of the accretion disk around the gainer in the case that there is enough space between both stars for this disk. Our code includes a complete description of the tidal interaction. The code was now extended with the action of magnetic braking. Without this phenomenon the rotational velocity of the gainer can not be predicted.Magnetic braking and tides act together and the evolution of the equatorial velocity can now be followed up from birth to death of the binary. From Figure (1) in the text one sees that the equatorial velocity is kept most of the time far below critical. When the equatorial velocity is large a magnetic field is created. The subsequent magnetic braking is applied on a large number of binaries for which the equatorial velocity is measured. The result is encouraging: a large fraction of observed equatorial velocities is reproduced by our calculations.
Bibliographical note6 pages, 2 figures, 2 tables