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

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

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.

AGB structure (1) Chieffi et al. (1998) Straniero et al. (2005) Cristallo (2006), PhD Thesis(*) Cristallo et al. (2007) (*) available at Earth-Sun (~200 R SUN ) CORE MAIN REFERENCES:

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

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

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

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

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

The models

The s-process: RESUME Z=1.4 x Z= 3.0 x Z=1.0 x Final distributions

YIELDS IsotopeM2 Z1p4m2M2 Z1m3M2 Z1m4 H-4.06e e e-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 e e-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

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

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

Effects of the Huge Pulse Nitrogen 12 C/ 13 C

Litium Heavy elements

The importance of using a FULL nuclear network FULLREDUCED

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?