Tidal forces and variability in close binary stars: the β-factor

We present the results of calculations that illustrate the effects, on orbital timescales, produced on the external layer of a star that is in a binary system in which the stellar rotation period is not synchronized with the orbital period. The calculations show how, for a fixed set of parameters, the amplitudes of the oscillations depend on stellar radius and on β, the ratio between the stellar rotation angular velocity and the orbital angular velocity.