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Nucleosynthesis of heavy elements in supernovae and
neutron-star mergers
Almudena Arcones
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Sneden, Cowan, Gallino 2008
GoldSilver Eu
Oldest observed starsThe very metal-deficient star
HE 0107-5240
Elemental abundances in:
- ultra metal-poor stars and
- solar system
‣Robust r-process for 56
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The r-process: what do we know?
• Solar system: residual r-process r-process peaks and path → fast neutron capture
• Astrophysical environment: explosive and high neutron density
• UMP stars: robust process from 2nd to 3rd peak contribution from other process(es) below 2nd peak
• Chemical evolution: r-process does not occur in every core-collapse supernovae
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The r-process: what do we know?
• Solar system: residual r-process r-process peaks and path → fast neutron capture
• Astrophysical environment: explosive and high neutron density
• UMP stars: robust process from 2nd to 3rd peak contribution from other process(es) below 2nd peak
• Chemical evolution: r-process does not occur in every core-collapse supernovae
What do we need to know better?• Astrophysical site(s)
• Nuclear physics
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Where does the r-process occur?Core-collapse supernovae Neutron star mergers
Cas A (Chandra X-Ray observatory) Neutron-star merger simulation (S. Rosswog)
Neutron stars
•neutrino-driven winds (Woosley et al. 1994,…)
•jets (Winteler et al. 2012)
•shocked surface layers (Ning, Qian, Meyer 2007)
•neutrino-induced in He shell (Banerjee, Haxton, Qian 2011)
•dynamic ejecta
•neutrino-driven winds
•evaporation disk
(Lattimer & Schramm 1974, Freiburghaus et al. 1999, ....)
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Neutrino-driven winds
neutrons and protons form α-particles α-particles recombine into seed nuclei
NSE → charged particle reactions / α-process → r-process
weak r-process
νp-processT = 10 - 8 GK 8 - 2 GK
T < 3 GKfor a review see Arcones & Thielemann (2013)
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time [s]
Radi
us [c
m]
ShockReverse
shock
Neutron
star
Arcones et al 2007
Which elements are produced in neutrino winds?
❒mass element
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time [s]
Radi
us [c
m]
ShockReverse
shock
Neutron
star
Arcones et al 2007
Which elements are produced in neutrino winds?
❒mass element
no r-
proc
ess
Silver
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Lighter heavy elements in neutrino-driven winds
neutron richproton rich
Arcones & Montes (2011) C.J. Hansen, Montes, Arcones (2014)
Overproduction at A=90, magic neutron number N=50 (Hoffman et al. 1996) suggests: only a fraction of neutron-rich ejecta (Wanajo et al. 2011)
Observation pattern reproduced!
Production of p-nuclei
νp-process weak r-process
observations Honda et al. 2006
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Lighter heavy elements in neutrino-driven winds
neutron richproton rich
observations
(Arcones & Montes, 2011)
Overproduction at A=90, magic neutron number N=50 (Hoffman et al. 1996) suggests: only a fraction of neutron-rich ejecta (Wanajo et al. 2011)
Observation pattern reproduced!
Production of p-nuclei
νp-process weak r-process
40 50 60 70 80 90 100 110Entropy [kB/nuc]
0.40
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
Ye
Sr
−8
−7
−6
−5
−4
−3
−2
−1
40 50 60 70 80 90 100 110Entropy [kB/nuc]
0.510.520.530.540.550.560.570.580.590.600.610.620.630.640.650.66
Ye
Sr
−15−14−13−12−11−10−9−8−7−6−5
Arcones & Bliss (2014)
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Lighter heavy elements: Sr - AgUltra metal-poor stars with high and low enrichment of heavy r-process nuclei suggest: at least two components or sites (Qian & Wasserburg):
Travaglio et al. 2004: solar=r-process+s-process+LEPP
Montes et al. 2007: solar LEPP ~ UMP LEPP → unique
Are Honda-like stars the outcome of one nucleosynthesis event or the combination of several?
log ε
Z
log ε
Z
or
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Nucleosynthesis componentsAbundance of many UMP stars can be explained by two components:
C.J. Hansen, Montes, Arcones (2014)
Component abundance pattern: YH and YL
Fit abundance as combination of components:
Ycalc(Z) = (CHYH(Z) + CLYL(Z)) · 10[Fe/H]
BS16089-013
= 0.152χ
-3
-2
-1
0
log
∈lo
g∈
-3
-2
-1
0
1
LEPP
r-process
Fit
2χ = 3.98
35 7570656055504540
Atomic number
H-componentL-component
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Sr/YSr/ZrSr/Ag
L-component in neutrino-driven winds
Observations point to proton-rich conditions
Nuclear physics uncertainties?
observations
observations
observations
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Key reactions: weak r-process
(α,n)
Bliss, Arcones, Montes, Pereira (in prep.)
10−9
10−8
10−7
10−6
10−5
10−4
10−3
10−2
abun
danc
e
Ye = 0.45baselineλ(α,n) · 10 for Z = 10− 30λ(α,n) · 0.1 for Z = 10− 30
10 15 20 25 30 35 40 45 50 55
Z
10−9
10−8
10−7
10−6
10−5
10−4
10−3
abun
danc
e
Ye = 0.45baselineλ(α,n) · 10 for Z = 30− 40λ(α,n) · 0.1 for Z = 30− 40
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Astrophysical site
Origin of elements from Sr to Ag
[Fe/H]
[Sr/F
e]
Hansen et al. 2013Nucleosynthesis: identify key reactions
Observations
Chemical evolution
ν wind
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Neutron star mergers
Rosswog 2013
disk evaporation
Ejecta from three regions:
• dynamical ejecta
• neutrino-driven wind
• disk evaporation
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Neutron star mergers: robust r-process
1.2M� � 1.4M� 1.4M� � 1.4M� 2M� � 1.4M�
nucleosynthesis of dynamical ejecta robust r-process:
- extreme neutron-rich conditions (Ye =0.04)
- several fission cycles
Korobkin, Rosswog, Arcones, Winteler (2012)
see also Bauswein, Goriely, and Janka
Hotokezaka, Kiuchi, Kyutoku, Sekiguchi, Shibata, Tanaka, Wanajo
Ramirez-Ruiz, Roberts, ...
Right conditions for a successful r-process (Lattimer & Schramm 1974, Freiburghaus et al. 1999)
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Neutron star mergers: robust r-process
1.2M� � 1.4M� 1.4M� � 1.4M� 2M� � 1.4M�
nucleosynthesis of dynamical ejecta robust r-process:
- extreme neutron-rich conditions (Ye =0.04)
- several fission cycles
Korobkin, Rosswog, Arcones, Winteler (2012)
see also Bauswein, Goriely, and Janka
Hotokezaka, Kiuchi, Kyutoku, Sekiguchi, Shibata, Tanaka, Wanajo
Ramirez-Ruiz, Roberts, ...
Right conditions for a successful r-process (Lattimer & Schramm 1974, Freiburghaus et al. 1999)
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4 3 2 1
Neutron star mergers: neutrino-driven windPerego et al. (2014)3D simulations after merger
disk and neutrino-wind evolution
neutrino emission and absorption
Nucleosynthesis: 17 000 tracers
see also Fernandez & Metzger 2013, Metzger & Fernandez 2014, Just et al. 2014, Sekiguchi et al.
Martin et al. (2015)
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Neutron star mergers: neutrino-driven wind
Martin et al. (2015)
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Neutron star mergers: neutrino-driven wind
Martin et al. (2015)
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Time and angle dependencyBlack hole formation determines time for wind nucleosynthesis (Fernandez & Metzger 2013, Kasen et al. 2015)
Early times: low Ye: heavy elements
Late times: Ye ~0.35: lighter heavy elements
angle dependency
Martin et al. (2015)
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Time and angle dependencyBlack hole formation determines time for wind nucleosynthesis (Fernandez & Metzger 2013, Kasen et al. 2015)
Early times: low Ye: heavy elements
Late times: Ye ~0.35: lighter heavy elements
angle dependency
Martin et al. (2015)
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dynamical ejecta
disk ejecta
Wind and dynamic ejectaWind ejecta complement dynamic ejecta
Complete mixing: solar system abundances and UMP stars
Martin et al. (2015)
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dynamical ejecta
disk ejecta
Wind and dynamic ejectaWind ejecta complement dynamic ejecta
Complete mixing: solar system abundances and UMP stars
Partial mixing: Honda-like star?
Martin et al. (2015)
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Nuclear physics input
Erler et al. (2012)
nuclear masses, beta decay, reaction rates (neutron capture), fission
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Impact of nuclear masses
• Different mass models
Mendoza-Temis et al. 2015
Meng-Ru Wu talk
e.g.,
Wanajo et al. 2004
Farouqi et al. 2010,
Arcones & Martinez-Pinedo 2011
Goriely et al. 2013
• Sensitivity studies Monte Carlo: all masses ± 1MeV Mumpower, Surman et al. 2015, 2016
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Abundances based on density functional theory
- six sets of different parametrisation (Erler et al. 2012)
- two realistic astrophysical scenarios: jet-like sn and neutron star mergers
First systematic uncertainty band for r-process abundances
Uncertainty band depends on A, in contrast to homogeneous band for all A e.g., Mumpower et al. 2015
Can we link masses to r-process abundances?
Nuclear masses: systematic uncertainty
Martin, Arcones, Nazarewicz, Olsen (2016)
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Two neutron separation energy
Nucleosynthesis path at constant Sn: (n,γ)-(γ,n) equilibrium
Neutron capture
Beta decay
S2n/2 = 1.5 MeV
Martin, Arcones, Nazarewicz, Olsen (2016)
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Two neutron separation energy
Nucleosynthesis path at constant Sn: (n,γ)-(γ,n) equilibrium
Neutron capture
Beta decay
S2n/2 = 1.5 MeV
Martin, Arcones, Nazarewicz, Olsen (2016)
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Two neutron separation energy: abundances
freeze-out abundances before decay
Martin, Arcones, Nazarewicz, Olsen (2016)
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Two neutron separation energy: abundances
freeze-out abundances before decay → final abundances
neutron capture during decay (Surmann & Engel 2001, Arcones & Martinez-Pinedo 2011)
Martin, Arcones, Nazarewicz, Olsen (2016)
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Two neutron separation energy: abundances
freeze-out abundances before decay → final abundances
neutron capture during decay (Surmann & Engel 2001, Arcones & Martinez-Pinedo 2011)
Martin, Arcones, Nazarewicz, Olsen (2016)
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ConclusionsHow many r-processes? How many astrophysical sites?lighter heavy elements (Sr-Y-Zr-...-Ag): neutrino-driven winds
heavy r-process: mergers: dynamical, wind, disk evaporation
jet-like supernovae
Improved supernova and merger simulations: EoS, neutrino rates
Neutron-rich nuclei: experiments with radioactive beams, theory
Observations: oldest stars, kilo/macronovae, neutrinos, gravitational waves, ...
Chemical evolution models
Needs
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