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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?