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

2. 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

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

4. Formation of Heavy Elements
Thermonuclear reactions A<56
Neutron captures
- slow (s-process)
free neutrons/cm3
- rapid (r-process)
free neutrons/cm3

5. s-process

6. 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

7. 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

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

9. IRAS

10. Extrinsic AGBs 2 1

11. HD
Allen & Barbuy 2006

12. 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