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 in to account diffusion and nuclear reactions. The first model was obtain ed with the diffusion coefficients given by Thoul et al.(1995). Its fr equencies show that the model should be improved. Five other models be en have obtained with modifications of the diffusion coefficients and/ or an increase of the opacity below the convective envelope. Several o f these models show definite improvements such that most of the remain ing sources of discrepancies are located in the convective envelope an d mainly in its outermost layers where the superadiabatic gradient is large. The models have also been compared with Basu's seismic model. I n 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 f requencies.