1. Why Galaxies care about Asymptotic Giant Branch stars S. Cristallo (INAF - Osservatorio Astronomico di Teramo) Collaborators: O. Straniero, R. Gallino, L. Piersanti, I. Dominguez, M.T. Lederer

2. OUTLINE The importance of AGB stars Major improvements on the stellar code (FRANEC) AGB nucleosynthesis and evolution at different metallicities Very low metallicity AGBs : chemical features

3. Why AGBs are so important… Excellent tracings of halo structures; IR emission (effects on integrated colors); tracers of intermediate age populations (IZw18); distance indicators (Mira); production sites of LIGHT & HEAVY elements.

4. AGB structure (1) Chieffi et al. (1998) Straniero et al. (2005) Cristallo (2006), PhD Thesis(*) Cristallo et al. (2007) (*) available at http://www.oa-teramo.inaf.it/osservatorio/personale/cristallo/pag_in_eng.html Earth-Sun (~200 R SUN ) CORE MAIN REFERENCES:

5. AGB structure (2) 22 Ne(α,n) 25 Mg 13 C(α,n) 16 O

6. The resulting 13 C pockets ΔM~10 -3 M X( 13 C eff )=X( 13 C)-X( 14 N)*13/14 1 st 11 th 14 N strong neutron poison via 14 N(n,p) 14 C reaction

7. About 500 isotopes linked by more than 700 reactions THE NETWORK LEGENDA: Light elements Heavy elements

8. M=2M Z=Z (Z=1.4x10 -2 ) C/O>1 C/O~2 Radiative burning of 13 C(α,n) 16 O reaction M=2M Z=1.0x10 -4 C/O~8 C/O~50 FRANEC

9. Molecular opacities T 2000 K4000-5000 K Atomic opacities Molecular opacities Grains Metallicity 12 C & 14 N enh. factors Solar 1.4 x 10 -2 ( * ) 1, 1.5, 1.8, 2.2, 4 3 x 10 -3 & 6 x 10 -3 ( * ) 1, 2, 5, 10, 50 1 x 10 -3 ( * ) 1, 5, 10, 50, 200 1 x 10 -4 (+) 1, 10, 100, 500, 2000 (+) Cristallo et al. 2007 (ApJ 667, 489) (*) Cristallo et al. in preparation O-rich regimeC-rich regime CO H 2 O TiO CN C 2 C 3 ……

10. The models

11. The s-process: RESUME Z=1.4 x 10 -2 Z= 3.0 x 10 -3 Z=1.0 x 10 -4 Final distributions

12. YIELDS IsotopeM2 Z1p4m2M2 Z1m3M2 Z1m4 H-4.06e-2-1.16e-1-9.92e-2 3 He3.77e-42.58e-41.83e-4 4 He3.23e-28.85e-27.99e-2 12 C5.84e-32.22e-21.71e-2 13 C5.16e-53.63e-66.97e-7 14 N1.31e-31.52e-43.40e-5 16 O-1.04e-54.47e-44.03e-4 17 O3.32e-57.09e-69.33e-7 18 O-5.65e-6-5.07e-7-3.20e-8 19 F8.17e-73.96e-62.44e-6 22 Ne7.06e-42.68e-31.41e-3 23 Na1.95e-53.24e-51.38e-5 24 Mg9.94e-67.33e-52.64e-5 25 Mg7.10e-74.36e-52.55e-5 26 Mg3.16e-63.16e-53.21e-5 26 Al3.06e-75.40e-83.18e-8 27 Al1.00e-61.88e-61.43e-6 Y1.18e-71.55e-81.08e-9 Ba1.91e-79.76e-84.42e-9 Pb4.36e-89.85e-71.09e-7

13. AGB evolution at very low metallicities M=2M SUN Z=10 -4 M=1.5M SUN Z=5 x 10 -5 Cristallo et al. 2007 (ApJ 667, 489)

14. The proton ingestion mechanism Low time steps Time dependent mixing Rapid structure reaction Coupling between phisical and chemical evolution Large neutron densities (n n ~10 15 cm -3 ) 700 isotopes & 1000 reactions Hollowell et al. (1990) Iwamoto et al. (2004) Suda et al. (2004) Straniero et al. (2005) Campbell et al. (2007) Work in progress!! M= 0.85 M M= 1.0 M M= 1.5 M M= 2.0 M M= 2.5 M Z= 5.0 x 10 -5

15. Effects of the Huge Pulse Nitrogen 12 C/ 13 C

16. Litium Heavy elements

17. The importance of using a FULL nuclear network FULLREDUCED

18. THE STATE OF THE ART First AGB models calculated with C-enhanced low temperature opacity coefficients, with the formation of a non-negligible 13 C-pocket and calculated with a complete nuclear network; AGB models at very low metallicity: an alternative scenario to the 13 C-pocket spread requested by observations?