Effects of diffusion and settling on solar modelling and helioseismology

Joergen Christensen-Dalsgaard

Abstract. Diffusion and settling of helium and heavier elements have been part of the `standard solar model' since around 1990, with substantial support from helioseismic analyses. I give a brief overview of the methods used and the results. In the solar case it seems that a relatively simple treatment of the heavy-element behaviour, representing all elements by, say, oxygen, is adequate, and that selective radiative effects play a minor role. Recently serious questions have been raised on the reliability of the solar models, as a result of a revision of the measures solar atmospheric abundances of oxygen, nitrogen and carbon.