Convective overshooting and production of s-nuclei in massive stars during their core He-burning phase

Abstract

Context. Many studies on the s-process and, more specifically, on the s-process weak component have been performed so far, but a detailed scrutiny of the impact of the stellar evolution modeling uncertainties on the efficiency of this nucleosynthesis process is still missing. Aims. We analyze the role of convective overshooting on the production of s-nuclei in massive stars during their core He-burning phase. Methods. With the "post-processing" technique we explore the role of the convective overshooting on the production of s-nuclei in stellar models of different initial mass and metallicity (15 ≤ MZAMS/M⊙ ≤ 25; 10-4 ≤ Z ≤ 0.02), considering a range of values for the parameter f, which determines the overall efficiency of convective overshooting. Results. We find enhancements in the production of s-nuclei until a factor ~6 (measured as the average overproduction factor of the 6 s-only nuclear species with 60 ≲ A ≲ 90) in all our models of different initial mass and metallicity with f in the range 0.01-0.035 (i.e. models with overshooting) compared to the production obtained with "no-overshooting" models (i.e. models with the same initial mass and metallicity, but f = 10-5). Moreover the results indicate that the link between the overshooting parameter f and the s-process efficiency is essentially monotonic in all our models of different initial mass and metallicity. Also evident is the higher s-process efficiency when we progressively increase for a given f value both the mass of the models from 15 M⊙ to 25 M⊙ and the Z value from 10-4 to 0.02. We also briefly discuss the possible consequences of these results for some open questions linked to the s-process weak component efficiency, as well as a "rule of thumb" to evaluate the impact of the convective overshooting on the yields of a generation of stars. © 2010 ESO.