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O. Straniero, L. Piersanti (Osservatorio di Teramo, INAF)
R. Gallino (Universita’ di Torino)
I. Dominguez (Univerdad de Granada)
Light and heavy elements nucleosynthesis in low
mass AGB Stars
S. Cristallo(Osservatorio di Teramo, INAF)
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OUTLINE
The formation of the 13C pocket and the nuclear network
Light and heavy elements nucleosynthesis
Comparison with observations
M=2M AGB models (FRANEC Code)
(Z=1.5x10-2 ≡ Z) (Z=1x10-4)
DISK STARS HALO STARS
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s-process
Z
Β stability
valley
N
Z
Weak component (A<90)
Main component (90<A<204)
Strong component (204<A<209)AGB
13C(α,n)16O reaction
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How we treat the convection
• Schwarzschild criterion: to determine convective borders
• Mixing length theory: to calculate velocities inside the convective zones
At the inner border of the convective At the inner border of the convective envelopeenvelope, we assume that the velocity , we assume that the velocity profile drops following an profile drops following an exponentially decaying lawexponentially decaying law
v = vbce · exp (-d/β Hp) • Vbce is the convective velocity at the
inner border of the convective envelope (CE)
• d is the distance from the CE
• Hp is the scale pressure height
• β = 0.1REF: Freytag (1996), Herwig (1997),REF: Freytag (1996), Herwig (1997),
Chieffi (2001), Straniero(2005), Chieffi (2001), Straniero(2005), Cristallo (2001,2004,2006)Cristallo (2001,2004,2006)
WARNING: vbce=0 except during Dredge Up episodes
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Gradients profiles WITHOUT exponentially decaying velocity profileGradients profiles WITH exponentially decaying velocity profile
CONVECTIVEENVELOPE
RADIATIVE He-INTERSHELL
Duringa TDUepisode
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Formation of the 13C-pocket
M=2M
Z=Z
a) Maximum envelope penetration (during TDU);
b) 12C(p,)13N(β+)13C and13C(p,)14N reactions;
c) 22Ne(p,)23Na;
d) the envelope receeds.
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The resulting pocket(s)
ΔM~10-3 M
13C-pocket
23Na-pocket
14N-pocket
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Variation of the 13C-pocket pulse by pulse
X(13Ceff)=X(13C)-X(14N)*13/14
1st 11th
14N strong neutron poison via
14N(n,p)14C reaction
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Calibration of the free parameter
Different choices ofthe β parameter in the velocity profile
algorithm
β~0.11. Low mass AGB Stars2. Treatment of convection
Cristallo S. (PhD Thesis)
H12C
14N13C
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About 500 isotopes
linked by more than linked by more than 700700 reactions reactions
Reactions Reference(n,γ)
(n,p) and (n,α)p and α captures
β decays
Bao & KaeppelerKoehler,Wagemans
NACRETakahashi&Yokoi
THE NETWORK
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Solarmetallicity
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First TDU episode andconsequent 13C-pocket
formation
THE AGB PHASETHE AGB PHASEM=2M
Z=Z
(Z=1.5x10-2)
Engulfment of the 13C-pocket in theconvective shell
Radiative burning of13C(α,n)16O reaction
C/O=1
C/O~2
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Convective 13C(α,n)16O
22Ne(α,n)25Mg
CONVECTIVE 13C burning 60Fe production
t=0 at the13C-pocket ingestion
in the convective shellCristallo et al. 2006 (astro-ph/0606374)
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1st TDUNO 60Fe
1st TDU26Al dredged up MAINLY
from the He-intershell
2nd TDUconvective 13C
60Fe
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Finaldistributions
Comparison with post-process calculations
POST PROCESS(Gallino et al. 1998)
M=2M , Z=2x10-2
(Straniero et al. 2003)
13C pocket 1. Artificially introduced
2. Constant pulse after pulse
1. Artificially introduced2. Constant pulse after pulse
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Comparison with Galactic Carbon Stars
Abia et al. 2002 FRANEC
( 6th pulse with TDU)
Surface C/O=1
[ls/Fe]=([Sr/Fe]+[Y/Fe]+[Zr/Fe])/3 [hs/Fe]=([Ba/Fe]+[La/Fe]+[Ce/Fe] +[Nd/Fe] +[Sm/Fe])/5
Z ~ Z
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Lowmetallicity
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[C/Fe]=3.3 deX
[F/Fe]=3.7 deX
[ls/Fe] ~ 1.7
[Pb/hs] ~ 3.1
[hs/Fe] ~ 2.3
[Na/Fe]=2.8 deX
Pulse by pulse surface enrichments (Z=10-4)
1
10
last
5
…
C-star Lead-star
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Comparison with LEAD (Halo) stars
(Van Eck et al. 2003)
McClure & Woodsworth 1990 ORBITAL PARAMETERS
REQUESTED DILUTION
EXTRINSIC AGB?√
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Future plans
• Exploring effects induced by C/O surface variations in models at low metallicities
• Performing new models with a reduced mass-loss
• Calculating more massive AGB stars (Al production)1. M=3M and Z=Z (already done)2. Currently running M=6M and Z=Z
Yields and pulse by pulse [El/Fe] soon available on-line at:
http://www.oa-teramo.inaf.it/osservatorio/personale/cristallo/data_online.html