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 http://www.oa-teramo.inaf.it/osservatorio/personale/cristallo/pag_in_eng.html

Earth-Sun(~200 RSUN)

CORE

MAIN REFERENCES:

AGB structure (2)

22Ne(α,n)25Mg

13C(α,n)16O

The resulting 13C pockets

ΔM~10-3 M

X(13Ceff)=X(13C)-X(14N)*13/14

1st

11th

14N strong neutron poison via14N(n,p)14C reaction

About 500 isotopeslinked by more than linked by more than 700700 reactions reactions

THE NETWORK

Ba134 Ba135 Ba136 Ba137 Ba138Cs133 Cs134 Cs135 Cs136 Cs137

Xe128 Xe129 Xe130 Xe131 Xe132 Xe133 Xe134 Xe135 Xe136I127 I128 I129 I130 I131 I132 I133

Te127 Te128 Te130

P31Si28 Si29 Si30 Si31

Al26 Al27Mg24 Mg25 Mg26

Na22 Na23 Na24Ne21 Ne22

(a,g) (p,g) (n,g) Beta Decay(a,n) (p,a) (n,p) (n,g)+alfa decay(a,p) 3alfa (n,a)

Zr90 Zr91Y89 Y90 Y91

Sr86 Sr87 Sr88 Sr89 Sr90 Sr91Rb85 Rb86 Rb87 Rb88

Kr83 Kr84 Kr85 Kr86 Kr87 Kr88Br83 Br84

Po210Bi209 Bi210

Pb204 Pb205 Pb206 Pb207 Pb208 Pb209 Pb210Tl203 Tl204 Tl205Hg203 Hg204

ALFA Decay

LEGENDA:Light elements

Heavy elements

M=2M

Z=Z

(Z=1.4x10-2)C/O>1

C/O~2

Radiative burning of13C(α,n)16O reaction

M=2M

Z=1.0x10-4

C/O~8

C/O~50

FRANEC

FRANEC

Molecular opacities

T2000 K 4000-5000 K

Atomic opacities

Molecular opacities

Grains

Metallicity 12C & 14N enh. factors

Solar ≡ 1.4x10-2 (*) 1, 1.5, 1.8, 2.2, 4

3x10-3 & 6x10-3 (*) 1, 2, 5, 10, 50

1x10-3 (*) 1, 5, 10, 50, 200

1x10-4 (+) 1, 10, 100, 500, 2000

(+) Cristallo et al. 2007 (ApJ 667, 489)

(*) Cristallo et al. in preparation

O-rich regime C-rich regime

COH2OTiO

CNC2

C3… …

The models

The s-process: RESUME

Z=1.4x10-2

Z= 3.0x10-3

Z=1.0x10-4

Finaldistributions

YIELDSIsotope M2 Z1p4m2 M2 Z1m3 M2 Z1m4

H -4.06e-2 -1.16e-1 -9.92e-23He 3.77e-4 2.58e-4 1.83e-44He 3.23e-2 8.85e-2 7.99e-212C 5.84e-3 2.22e-2 1.71e-213C 5.16e-5 3.63e-6 6.97e-714N 1.31e-3 1.52e-4 3.40e-516O -1.04e-5 4.47e-4 4.03e-417O 3.32e-5 7.09e-6 9.33e-718O -5.65e-6 -5.07e-7 -3.20e-819F 8.17e-7 3.96e-6 2.44e-6

22Ne 7.06e-4 2.68e-3 1.41e-323Na 1.95e-5 3.24e-5 1.38e-524Mg 9.94e-6 7.33e-5 2.64e-525Mg 7.10e-7 4.36e-5 2.55e-526Mg 3.16e-6 3.16e-5 3.21e-526Al 3.06e-7 5.40e-8 3.18e-827Al 1.00e-6 1.88e-6 1.43e-6

Y 1.18e-7 1.55e-8 1.08e-9

Ba 1.91e-7 9.76e-8 4.42e-9

Pb 4.36e-8 9.85e-7 1.09e-7

AGB evolution at very low metallicities

M=2MSUN

Z=10-4

M=1.5MSUN

Z=5x10-5

Cristallo et al. 2007(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 (nn~1015 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 theHuge Pulse

Nitrogen

12C/13C

Litium

Heavy elements

The importance of using a FULL nuclear network

FULL REDUCED

THE STATE OF THE ART

• First AGB models calculated with C-enhanced low temperature opacity coefficients, with the formation of a non-negligible 13C-pocket and calculated with a complete nuclear network;

• AGB models at very low metallicity: an alternative scenario to the 13C-pocket spread requested by observations?