Element Diffusion and Accretion in Metal Poor Stars
  The abundances of the chemical elements observed at the surface of metal-poor stars are not always representative of their initial values. During stellar evolution, various physical processes modify their internal composition. In this short paper, in honor of George W. Preston, I remind the importance of atomic diffusion, and the possible effects of accretion processes which may lead to double-diffusive (thermohaline) instabilities. I discuss the consequences of these processes and compare them to current observations. 
Sylvie Vauclair ((1) Institut de Recherches en Astrophysique et   Plan'etologie, CNRS, Universit'e Paul Sabatier, Toulouse, ...
astro-ph.SR