Variation as a function of the Lagrangian mass coordinate of the shear diffusion coefficient in the radiative envelope of our 15 M_⊙ model. The continuous lines refer to the spin-up case with an initial orbital period of 1.4 days. The dashed lines show the case when the initial orbital period is equal to 1.0 days. The curves for the periods equal to 1.0 and 1.4 days, corresponding to an age of 113 000 years, are the same and thus are superposed. The different colors have the same meaning as in Fig. 2.