Abstract
AbstractThe effect of gravitational settling and radiation driven diffusion on the evolution of stars near the main sequence is reviewed. New simplified formulae for calculating diffusion are proposed that improve on previous such formulae. The reliability of available diffusion coefficients is discussed and areas where further work is needed are identified. Newly available opacity calculations are used to estimate the effects of radiative acceleration on Fe.The size of the modifications to the evolution are shown to be modest: a reduction of order 10% on the evolutionary age of globular clusters. There are indications from the Li abundance in the high Teff halo stars that some turbulence is present below the convection zone. Models calibrated using solar properties reproduce the Teff at which the Li gap is observed in F stars as well as its depth without any arbitrary parameter. Similarly the presence of AmFm stars is explained over the Teff range where they are observed.
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