Evolution of the nitrogen abundance at the surface as a function of the surface velocity for the same models as those shown in Fig. 4. The abundances are expressed as ratios between the number of ¹⁴N atoms to the number of H atoms, normalized to a number of 10¹² H atoms. Left panel: the star begins its evolution with a rotation on the ZAMS equal to 310 km s^-1. In the close binary considered, the star is spun down by tidal forces. Right panel: the star begins its evolution with a rotation on the ZAMS equal to 60 km s^-1. In the close binary considered, the star is spun up by tidal forces.