Stellar Models with Microscopic Di usion and Rotational Mixing I: Application to the Sun

The Yale stellar evolution code has been modi ed to include the combined e ects of di usion and rotational mixing on 1 H, 4 He and the trace elements 3 He, 6 Li, 7 Li, and 9 Be. The interaction between rotational mixing and di usion is studied by calculating a number of calibrated solar models. The rotational mixing inhibits the di usion in the outer parts of the models, leading to a decrease in the envelope di usion by 25 { 50%. Conversely, di usion leads to gradients in mean molecular weight which can inhibit the rotational mixing. The degree to which gradients in mean molecular weight inhibits the rotational mixing is somewhat uncertain. A comparison to the observed solar oblateness suggests that gradients in the mean molecular weight play a smaller role in inhibiting the rotational mixing previously believed. This is reinforced by the fact that the model with the standard value for the inhibiting e ect of mean molecular weight on the rotational mixing depletes no Li on the main sequence. This is in clear contrast to the observations. A reduction in the inhibiting e ect of mean molecular weight gradients by a factor of ten leads to noticeable main sequence Li depletion. Subject headings: stars: interiors { stars: rotation { stars: abundances { sun: rotation