The s - process weak component : uncertainties due to convection theory

Using a new s-nucleosynthesis code coupled with the stellar evolution code Star2003, simulations have been performed to study the impact of convection treatment on the s-process during core He-burning of a 25 M⊙ star (ZAMS mass) with initial solar metallicity. A diffusive approach, with the diffusion constant proportional to the convective velocity obtained from the mixing length theory, has been used to model mixing. Particular attention has been devoted to the role played by convective overshooting, to analyse how the s-process efficiency is influenced by the particular choice of the overshooting parameter value. The results show enhancements of about a factor 2-3 in s-process efficiency (measured as the average overproduction factor of the 6 s-only nuclear species with 60 . A . 90) with overshooting parameter values in the range 0.01-0.04, compared to results obtained with the same model but without overshooting. The impact of these results on the p-process model based on type II supernovae is discussed.