stellar evolution and nucleasysthesis(depending on the initial mass and composition of the star)...
TRANSCRIPT
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16.05.07 Markus Wadepuhl
Stellar evolution and Stellar evolution and
nucleosynthesisnucleosynthesis
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16.05.07 Markus Wadepuhl
OutlineOutline� The sun: models and nuclear reactions
– pp-chain
– CNO-cycle
� Steps in nucleosynthesis
– He-burning
– C-burning
– O-burning
� Uncertainties
� The share of stellar nucleosynthesis in galactical abundance
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16.05.07 Markus Wadepuhl
The stellar modelThe stellar model� Needs to follow the basic equations of
stellar evolution
ρπ 24
1
rm
r=
∂
∂2
2
244
1
4 t
r
rr
Gm
m
P
∂
∂−−=
∂
∂
ππ t
P
t
Tc
m
lpn
∂
∂+
∂
∂−−=
∂
∂
ρ
δεε υ
∇−=∂
∂
Pr
GmT
m
T44π
−=
∂
∂∑∑
k
ik
j
jiii rr
m
t
X
ρ
� Inserting the known values for the sun yields
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16.05.07 Markus Wadepuhl
The solar modelThe solar model
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16.05.07 Markus Wadepuhl
The The pppp--chain (Tchain (T66 < 15)< 15)
� first step very unusual due to the β+ decay at
the time of the closest approach
� pp II and pp III gain in importance with
increasing temperature
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16.05.07 Markus Wadepuhl
The CNOThe CNO--cycle (Tcycle (T66 < 50)< 50)
� C, N and O act similar to catalysts
� Maincycle dominates (≈ 1000 times)
�14N acts as a „bottleneck“
– Nearly all initially present C, N and O nuclei
will be found as 14N
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16.05.07 Markus Wadepuhl
The CNOThe CNO--cyclecycle
� With increasing
temperature the CNO-
cycle gains in
importance
� Other situation for
population III stars
(no CNO cycle)
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16.05.07 Markus Wadepuhl
Solar NeutrinosSolar Neutrinos
� pp-chain as well as the CNO-cycle produce
a characteristic neutrino spectrum
� neutrinos can easily escape and carry away
their energy
� good test for solar models
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16.05.07 Markus Wadepuhl
Steps in nucleosynthesisSteps in nucleosynthesis
� after Hydrogen is exhausted, there are
several burning stages that can be ignited at
higher and higher temperatures
(depending on the initial mass and
composition of the star)
� different burning stages can occur parallel
in different regions of the star
(shell burning, onion skin structure)
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16.05.07 Markus Wadepuhl
Steps in nucleosynthesisSteps in nucleosynthesis� during carbon burning and the later stages
many neutrinos are produced
– high energy loss by neutrino emission
Woosley et. al., 2002, RvMP, 74, 1016
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16.05.07 Markus Wadepuhl
Helium Burning (THelium Burning (T88 > 1)> 1)
BeHeHe844 ⇔+ � Decays after ≈ 10-16 s
γ+→+ CHeBe 1248
γ+→+ OHeC 16412
γ+→+ NeHeO 20416
� Following processes possible but in typical
stellar-environment very rare
( ) ( ) ( ) ( ) MgnNeOeFN 2522181814 ,,, αγαυγα +
� Produces free n that can form heavy
Elements (A ≥ 60)
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16.05.07 Markus Wadepuhl
Carbon Burning (TCarbon Burning (T88 = 5..10)= 5..10)
pNaCC +→+ 231212
α+→+ NeCC 201212
( ) NepNa 2023 ,α
� p and α find themselfes at extremely high
temperatures (too high for H and He burning)
� New reactions with other particles in the mixture
( ) ( ) ( ) OnCeNpC 16131312 ,, αυγ +
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PhotodisintegrationPhotodisintegration
(Neon Burning)(Neon Burning)� For T9 > 1 photodisintegration occurs
( ) ONe 1620 ,αγ
� Several following reactions are possible
γγ ++→+ MgONe 2416202
( ) ( ) ( ) SiMgNeO 28242016 ,,, γαγαγα
( ) SinMg 2825 ,α ( ) SinMg 2926 ,α ( ) AlnpMg 2626 ,
( ) SiMg 3026 ,γα ( ) SipAl 3027 ,α ( ) PpSi 3130 ,γ
� Main energy production via
( ) AlpMg 2625 ,γ
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Oxygen Burning (TOxygen Burning (T99 > 1)> 1)
pPOO +→+ 311616 α+→+ SiOO 281616
� same problem with p and α as during the carbon
burning
� Produces many nuclei e. g.28Si, 32,33,34S, 35,37Cl, 36,38Ar, 39,41K, 40,42Ca
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16.05.07 Markus Wadepuhl
PhotodisintegrationPhotodisintegration
(Silicon Burning)(Silicon Burning)
� at even higher temperatures (T9 > 3) 28Si can also
be decomposed
� n, p and α react with 28Si and build gradually
heavier nuclei until 56Fe is reached
( ) ( ) ( ) ( ) ( )ααγαγαγαγαγ 2,,,,, 1216202428 CONeMgSi
( ) ( ) ( ) ( ) ( ) SinSinSipPpSSi 282930313228 ,,,,, γγγγγα
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Chronological DevelopmentChronological Development
Woosley et. al., 2002, RvMP, 74, 1016
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16.05.07 Markus Wadepuhl
Chronological DevelopmentChronological Development
Woosley et. al., 2002, RvMP, 74, 1016
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Chronological DevelopmentChronological Development
� onion skin structure
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UncertaintiesUncertainties
� Convection
– Diffusion coefficient is modeled with a typical
mixing length
– Nuclear burning is carried out first
– Afterwards mixing is applied
� Nuclear reaction rates( ) OC 1612 ,γα ( ) MgnNe 2522 ,α
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ConvectionConvection
Woosley et. al., 2002, RvMP, 74, 1016
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16.05.07 Markus Wadepuhl
ConvectionConvection
Woosley et. al., 2002, RvMP, 74, 1016
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16.05.07 Markus Wadepuhl
ConvectionConvection
Woosley et. al., 2002, RvMP, 74, 1016
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ConvectionConvection
Woosley et. al., 2002, RvMP, 74, 1016
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UncertaintiesUncertainties� rotation
– centrifugal effects
– transfer of angular momentum may cause wind
� magnetic fields
– cause magnetic torques between differencially
rotating shells
� binaries
– Mass transfer between the two components if Roche
lobe is crossed
� winds
– depends crucially on the inital mass and metallicity
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Mass lossMass loss
Woosley et. al., 2002, RvMP, 74, 1016
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Mass lossMass loss
Woosley et. al., 2002, RvMP, 74, 1016
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The influence of metallicityThe influence of metallicity
Heger et al., 2003, APJ, 591, 288
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Chemical compositionChemical composition
Woosley et. al., 2002, RvMP, 74, 1016
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Chemical compositionChemical composition
Woosley et. al., 2002, RvMP, 74, 1016
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The ISM yield The ISM yield
� Winds
– Not well understood
� SNe
– mass cut
– explosion mechanism
– consider fallback
– very complicated explosive processes
� Plot the production factor
– Xi / Xi sol
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Chemical compositionChemical composition
Woosley et. al., 2002, RvMP, 74, 1016
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Special issuesSpecial issues
� especially metal-poor population III stars
possibly were very massiv
– maybe different SNe mechanism
� unknown mass cut
� rather simple explosion modeling
– Piston model
� only very few detailed SN observations
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16.05.07 Markus Wadepuhl
ReferencesReferences
� A. Unsöld & B. Baschek. Der neue Kosmos. Springer, Berlin, 2005
� R. Kippenhahn & A. Weigert, Stellar Structur and Evolution, Springer, Berlin, 1990
� D. Arnett, Supernovae and Nucleosynthesis, Princeton University Press, Princeton, 1996
� G. Wallerstein et al. Synthesis of the elements in stars: forty years of progress. RvMP 69: 995 – 1084, 1997
� S. E. Woosley et al. The evolution and explosion of massive stars. RvMP 74: 1015 – 1064, 2002
� A. Heger et al. The nucleosynthetic signature of population III. ApJ 567: 532 – 543, 2002
� K. Nomoto et al. Hypernovae and their Nucleosynthesis. Astro-ph/0209064
� A. Heger et al. How massive single stars end their life. ApJ 591: 288 – 300, 2003
� T. Rauscher et al. Nucleosynthesis in massive stars with improved nuclear and stellar physics. Astro-ph/0112478v2