The s-process nucleosynthesis in massive stars: current status and   uncertainties due to convective overshooting
  Context: It is well known that the so-called s-process is responsible for the production of neutron-rich trans-iron elements, that form the bulk of the "heavy nuclides" (i.e. nuclides more massive than the iron-group nuclei) in the solar-system composition, considered as "standard of reference" dataset for cosmic abundances. In particular, the s-process produces about half of all the trans-iron isotopes by moving along the "valley of stability" through a series of neutron capture reactions and beta decays. More than one s-process "component" (i.e. a nucleosynthesis event with a single set of physical conditions like neutron exposure, initial abundances and neutron density) is required in order to explain the observed solar distribution of s-nuclei abundances. Current views on the subject suggest the existence of several components that, in terms of stellar environments, correspond to distinct categories of stars in different evolutionary phases. Aims: The purpose of the chapter is to review the s-process nucleosynthesis occurring in massive stars (so-called weak component of s-process), pointing particular attention on the recent studies devoted to analyze how the uncertainties due to stellar evolution modeling and, specifically, due to convective overshooting affect the efficiency of this nucleosynthesis process. 
M. L. Pumo
astro-ph.SR