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)
CORE
Earth-Sun
(~200 RSUN)
MAIN REFERENCES:
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
AGB structure (2)
13C(α,n)16O
22Ne(α,n)25Mg
The resulting 13C pockets
X(13Ceff)=X(13C)-X(14N)*13/14
1st
ΔM~10-3 M
14N
11th
strong neutron poison via
14N(n,p)14C reaction
THE NETWORK
About 500 isotopes
linked by more than 700 reactions
LEGENDA:
(a,g)
(a,n)
(a,p)
Kr83
Br83
Kr84
Br84
(p,g)
(p,a)
3alfa
Rb85
Kr85
Sr86
Rb86
Kr86
(n,g)
(n,p)
(n,a)
Sr87
Rb87
Kr87
Sr88
Rb88
Kr88
Y89
Sr89
Light elements
Beta Decay
(n,g)+alfa decay
Zr90
Y90
Sr90
Zr91
Y91
Sr91
Si28
Ne21
Na22
Ne22
Na23
Mg24
Na24
Heavy elements
ALFA Decay
Ba134 Ba135 Ba136 Ba137 Ba138
Cs133 Cs134 Cs135 Cs136 Cs137
Xe128 Xe129 Xe130 Xe131 Xe132 Xe133 Xe134 Xe135 Xe136
I127
I128
I129
I130
I131
I132
I133
Te127 Te128
Te130
Po210
Bi209 Bi210
Pb204 Pb205 Pb206 Pb207 Pb208 Pb209 Pb210
Tl203 Tl204 Tl205
Hg203 Hg204
Mg25
Al26
Mg26
Al27
Si29
Si30
P31
Si31
C/O~2
C/O>1
M=2M
Z=Z
(Z=1.4x10-2)
Radiative burning of
13C(α,n)16O reaction
FRANEC
C/O~50
C/O~8
FRANEC
M=2M
Z=1.0x10-4
Molecular opacities
Grains
Molecular
opacities
2000 K
TiO1x10-4
(+)
T
4000-5000 K
Metallicity
O-rich
regime
Solar ≡ 1.4x10-2 (*)
CO
3x10-3 & 6x10-3 (*)
H2O1x10-3 (*)
Atomic
opacities
12C
14N enh. factors
&
C-rich regime
1, 1.5, 1.8, 2.2, 4
CN
1, 2, 5, 10, 50
C1,25, 10, 50, 200
… 1,C10,3 100, 500, 2000…
(*) Cristallo et al. in preparation
(+) Cristallo et al. 2007 (ApJ 667, 489)
The models
The s-process: RESUME
Z=1.4x10-2
Z= 3.0x10-3
Z=1.0x10-4
Final
distributions
YIELDS
Isotope
M2 Z1p4m2
M2 Z1m3
M2 Z1m4
H
-4.06e-2
-1.16e-1
-9.92e-2
3He
3.77e-4
2.58e-4
1.83e-4
4He
3.23e-2
8.85e-2
7.99e-2
12C
5.84e-3
2.22e-2
1.71e-2
13C
5.16e-5
3.63e-6
6.97e-7
14N
1.31e-3
1.52e-4
3.40e-5
16O
-1.04e-5
4.47e-4
4.03e-4
17O
3.32e-5
7.09e-6
9.33e-7
18O
-5.65e-6
-5.07e-7
-3.20e-8
19F
8.17e-7
3.96e-6
2.44e-6
22Ne
7.06e-4
2.68e-3
1.41e-3
23Na
1.95e-5
3.24e-5
1.38e-5
24Mg
9.94e-6
7.33e-5
2.64e-5
25Mg
7.10e-7
4.36e-5
2.55e-5
26Mg
3.16e-6
3.16e-5
3.21e-5
26Al
3.06e-7
5.40e-8
3.18e-8
27Al
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
Work in progress!!
Z= 5.0 x 10-5
M= 0.85 M
M= 1.0 M
M= 1.5 M
M= 2.0 M
M= 2.5 M
Hollowell et al. (1990)
Iwamoto et al. (2004)
Suda et al. (2004)
Straniero et al. (2005)
Campbell et al. (2007)
Effects of the
Huge 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?