Influence of hydrogen diffusion on the solar p-mode spectrum

We have introduced hydrogen diffusion in our evolution code in such a way that the chemical composition is computed taking simultaneously into account diffusion and nuclear reactions. The first model was obtained with the diffusion coefficients given by Thoul et al.(1995). Its frequencies show that the model should be improved. Five other models been have obtained with modifications of the diffusion coefficients and/or an increase of the opacity below the convective envelope. Several of these models show definite improvements such that most of the remaining sources of discrepancies are located in the convective envelope and mainly in its outermost layers where the superadiabatic gradient is large. The models have also been compared with Basu’s seismic model. In the domain of confidence of the latter,the relative differences in sound speed is less than 0.1% for models which fit best the observed frequencies.