A new study of s-process nucleosynthesis in massive stars

We present a comprehensive study of s-process nucleosynthesis in 15, 20, 25, and 30 M. stellar models having solar-like initial composition. The stars are evolved up to ignition of central neon with a 659 species network coupled to the stellar models. In this way, the initial composition from one burning phase to another is consistently determined, especially with respect to neutron capture reactions. The aim of our calculations is to gain a full account of the s-process yield from massive stars. In the present work, we describe our code in detail and then focus primarily on results from the s-process during central helium burning. We also illuminate some major uncertainties affecting the calculations. In order to motivate future work on burning in advanced stellar phases, we briefly present some results on the s-process in carbon shell burning; however, we leave a complete analysis of the s-process during the advanced evolutionary phases to a subsequent paper. Our results can help to constrain the yield of the s-process material from massive stars during their presupernova evolution.