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Description
A large sample of carbon-enhanced metal-poor stars enriched in s-process elements (CEMP-s) have been observed in the Galactic halo. These stars of low mass (M~0.9M_{sun}_) are located on the main-sequence or the red-giant phase, and do not undergo third dredge-up (TDU) episodes. The s-process enhancement is most plausibly due to accretion in a binary system from a more massive companion when on the asymptotic giant branch (AGB) phase (now a white dwarf). In order to interpret the spectroscopic observations, updated AGB models are needed to follow in detail the s-process nucleosynthesis. We present nucleosynthesis calculations based on AGB stellar models obtained with Frascati Raphson-Newton Evolutionary Code (FRANEC) for low initial stellar masses and low metallicities. For a given metallicity, a wide spread in the abundance of the s-process elements is obtained by varying the amount of 13C and its profile in the pocket, where the 13C({alpha}, n)16O reaction is the major neutron source, releasing neutrons in radiative conditions during the interpulse phase. We also account for the second neutron source ^22^Ne({alpha},n)^25^Mg, partially activated during convective thermal pulses.
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