Left panel: evolution of the abundance ratio N/C at the surface of 15 M_⊙ models at Z = 0.014 with an initial equatorial velocity of ~135 km s^-1 as a function of lgT_eff. Binary models correspond to 15 M_⊙ with the same characteristics as indicated above but with a 10 M_⊙ companion and an initial orbital period of 1.4 days. Right panel: evolution of the surface equatorial velocity as a function of time for the same models as in the left panel. The colours indicate the ratio between the central angular velocity and the surface velocity.