New Solar Models Including Helioseismological Constraints and Light-Element Depletion

We have computed new solar models using the same stellar evolution code as described in Charbonnel, Vauclair and Zahn (1992). This code, originating from Geneva, now includes the computation of element segregation for helium and 12 heavier isotopes. It may also include any type of mixing of the stellar gas, provided this mixing can be parametrized with an effective diffusion coefficient as a function of radius. Here we introduced rotationinduced mixing as prescribed by Zahn (1992). We present five solar models: 1) the standard model, computed with heavy element abundances as given by Grevesse (1991); 2) a model including pure element segregation (no mixing outside the convective zone) with Grevesse (1991) as initial abundances; 3) same model as (2), but iterated so that the final abundances are those of Grevesse (1991); 4) a model with both element segregation and rotation-induced mixing, leading to lithium and beryllium depletion consistent with the observations, with Grevesse (1991) as initial abundances; 5) same model as (4) but iterated to obtain Grevesse (1991) as final abundances. This model (5) now represents our best new solar model consistent with the observations. The u = P ρ function computed as a function of radius in these new solar models are compared to the helioseismological results obtained for the same function by Dziembowski et al (1994). Improving the physics of the models leads to a better consistency with helioseismology. In our best model (5), which includes both segregation and mixing, the relative difference in the u function between the model and the helioseismological results is smaller than 0.5 per cent at all radii except at the center and the surface. Meanwhile lithium is depleted by a factor 155 and beryllium by a factor 2.9, which is consistent with the observations. The bottom of the convective zone lies at a fractional radius of 0.716, consistent with helioseismology. The neutrino fluxes are not decreased in any of these models. Send offprint requests to: S. Vauclair The models including the computations of element segregation lead to a present surface helium abundance of: Ysurf between 0.248 and 0.258, which is in satisfactory agreement with the value derived from helioseismology.