ATOMIC DIFFUSION AND STELLAR EVOLUTION

Stellar models including atomic diffusion processes (gravitational settling, radiative accelerations, thermal diffusion, in addition to the purely diffusive term) have now been evolved throughout most of stellar evolution. We review some of the major roles of diffusion processes in stellar evolution. The emphasis is on interior properties. Examples include Populations I and II stars. It is emphasized that competing advective processes such as mass loss or meridional circulation modify internal concentrations differently from turbulent diffusion even when they lead to the same surface abundances. Radiative accelerations play a major role in horizontal branch and sdB stars.