The diversity of stellar nucleosynthesis sites in the s- to i-process and n-process range

Based on modern stellar simulations and observations, at least four different neutron-capture processes are needed to explain the production of heavy elements beyond iron in stars. The slow neutron-capture process (s-process) and the rapid neutron-capture process (r-process) were introduced decades ago in order to explain the solar system abundances, even before detailed stellar computational simulations were available. Recently, the existence of the intermediate neutron-capture process (i-process) was confirmed, with typical neutron densities in the order of 10¹³-10¹⁶ neutrons cm^-3 in-between the s-process and the r-process. The i-process explains a number of puzzling observations in stars with different metallicities and in presolar grains, all of them not compatible with neither the s-process and the r-process signatures. Finally, the n-process is a neutron-capture process activated in Core-Collapse Supernovae, with peak neutron density generated typically larger than 10¹⁸ neutrons cm^-3. Its signature has been identified in presolar grains. The ¹³C(α,n)¹⁶O reaction is a crucial source of neutrons to power the s-process and the i-process production, and the ²²Ne(α,n)²⁵Mg is a neutron source for the s-process and the n-process. In this contribution I will give an introduction to the diversity of the nucleosynthesis sites where the s-process, the i-process and the n-process are activated. I will also discuss their observational signatures and current needs from stellar theory and nuclear astrophysics to improve our present understanding of these processes.