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

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 ≤ M_ZAMS/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.

Tables A.1 and A.2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/524/A45