Variations in time of the orbital period (top) and geometrical parameters of the binary with initial masses 1.2 + 0.6 M_⊙ and initial period of 2.8 d. Short vertical bars denote: 1 – beginning of the fast mass transfer phase from star “1” to star “2”, 2 – end of the fast mass transfer phase, 3 – rapid increase of radius and moment of inertia of star “2” resulting in instability.