CEMP (s- and r/s) stars: s- and i-process and implications for Galactic chemical evolution

Abstract

Low-mass and low-metallicity Aymptotic Giant Branch (AGB) stars contribute to the chemical evolution of heavy elements through slow (s) and intermediate (i) neutron-capture processes. During AGB stars evolution the i-process occur when protons are mixed in a convective helium burning zone often termed as the proton ingestion event (PIE), and the s-process takes place in the interiors of Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) stars. CEMP (s and r/s) stars are main-sequence and giants that receive from their evolved binary companions material exposed to s- and i-process nucleosynthesis. As post-interacting binaries, these stars figure as powerful tracers of s- and i-process nucleosynthesis, evolution of binary systems and mechanisms of mass-transfer. Some highlights of results obtained from high-resolution spectroscopic studies of a sample of CEMP-s and CEMP-r/s stars are discussed in the light of observational evidence for the operation of s- and i- neutron-capture processes.