LUTH, Observatoire de Paris, 5 place Janssen, 92195 Meudon, France
Due to radiative acceleration and gravitational settling, stars would display vast differences in their surface composition, if these were not smoothed out, at least partly, by some competing processes. Possible mechanisms have been suggested and examined by Georges Michaud and his collaborators: mass loss, turbulent mixing and meridional circulation. They will be discussed here in the light of more recent developments.
(Online publication January 13 2006)