Atomic Diffusion and Radiative Accelerations in Stars

Atomic diffusion can have detectable effects in many kinds of stars, each time that mixing processes are not efficient enough to prevent the build up of abundance stratifications. In this talk, after presentation of some general aspects about diffusion processes in stars, I will discuss the role of radiative acceleration which is one of the important quantities determining diffusion velocities. I will also discuss some aspects specific to stellar atmospheres, in particular for stars exhibiting strong magnetic fields.