Study of the s-process in low mass stars of Galactic disc metallicity Laura Husti Roberto Gallino Sara Bisterzo

Outline: Origin of the heavy elements. Stellar Nucleosynthesis and Evolution. S-process nucleosynthesis in AGB stars at solar metallicity. Comparison with spectroscopic data of intrinsic and extrinsic AGBs

Where are the elements made? We want to address these issues using samples from the types of stars where nucleosynthesis occurs

Formation of Heavy Elements Thermonuclear reactions A<56 Neutron captures - slow (s-process) 105-1011 free neutrons/cm3 - rapid (r-process) 1022-1025 free neutrons/cm3

s-process

Stellar evolution of low mass stars Core H burning Core H exhaustion and contraction of the star H-shell ignition → core contraction + envelope expansion First dredge-up Core He burning Core He exhaustion; contraction of the C-O core Degenerate C-O core + alternate burning H and He shells + He intershell + extended convective envelope

Nucleosynthesis in AGB Stars Neutron sources: radiative 13C(α,n)16O convective 22Ne(α,n)25Mg 22Ne formation: 14 N(α,γ)18F(β+,ν)18O(α,γ) 22Ne 13C formation: 12C(p, γ) 13 N(β+,ν) 13C(p, γ) 14 N Busso, Gallino &Wasserburg ARA&A 1999

Variuos 13C pocket efficiencies, same metallicity hs(Ba, La, Cs, Nd,Sm) ls(Sr, Y, Zr) Pb

IRAS 0713+1005

Extrinsic AGBs 2 1

HD 123585 Allen & Barbuy 2006

Conclusions comparison between theoretical models and spectroscopic observations for the element abundances of 30 barium stars and 12 post-AGB stars models succesfully reproduce the observational data