The effect of diffusion on solar evolution

We examine the effect of element diffusion on the evolution of the Sun. We include partial ionization and diffusion of all elements, a new network of nuclear reactions which includes the reactions of the light elements like Li⁷ and Be⁹, and we follow the full evolution and depletion of these elements from the pre-main-sequence phase to the present stage. Our major conclusions are : The effect of diffusion on the predicted primordial hydrogen and helium abundances is ΔX = +0.025, ΔY = -0.024. However, the global effect of diffusion on the structure of the Sun is small, as was found by Bahcall & Pinsonneault. More specifically, we find that diffusion leads to ΔT_c/T = +0.003, Δp_c/p = 0.01 [where AQ_C = Q (with diffusion) - Q(no diffusion) for a quantity Q at the center] at the center and ΔT_s/T = +0.05%, Δp_s/p = 0.09% at the surface. [Here ΔQ_s = Q(with diffusion) - Q(no diffusion) for a quantity Q on the surface]. We obtain the depletion of light elements Li⁷ and Be⁹ due to both diffusion and nuclear reactions and find that diffusion enhances the depletion at the surface by 1.08.