Résumé
A number of main-sequence B-type stars, e.g., v Eri, K Cen, a Car, and K Vel, present oscillations that may be accounted for by opacity mechanisms as long as the stellar opacity is larger than the computed standard, at least in some specific layers. This has been studied by several authors who computed ad hoc opacity profiles that reproduced the observations. We show here that atomic diffusion, which causes elements to move selectively inside the star under the main effects of gravity and radiative accelerations, may be the reason for these opacity enhancements. The radiative accelerations of specific elements are the result of photon absorption, which depends on the ionization stage. For this reason, the elements accumulate in layers close to the region where they maximize their contribution to the global opacity, increasing the opacity at the right place in a natural way. We present preliminary results obtained for a 9.5 Mo model.