Nucleosynthesis of heavy elements in supernovae and 


neutron-star mergers

Almudena Arcones

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

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

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

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, ....)

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)

time [s]

Radi

us [c

m]

ShockReverse

shock

Neutron

star

Arcones et al 2007

Which elements are produced in neutrino winds?

❒mass element

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

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

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)

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

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

Sr/YSr/ZrSr/Ag

L-component in neutrino-driven winds

Observations point to
proton-rich conditions

Nuclear physics uncertainties?

observations

observations

observations

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

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

Neutron star mergers

Rosswog 2013

disk evaporation

Ejecta from three regions:

• dynamical ejecta

• neutrino-driven wind

• disk evaporation


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)

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)

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)

Neutron star mergers: neutrino-driven wind

Martin et al. (2015)

Neutron star mergers: neutrino-driven wind

Martin et al. (2015)

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)

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)

dynamical ejecta

disk ejecta

Wind and dynamic ejectaWind ejecta complement dynamic ejecta

Complete mixing: solar system abundances and UMP stars

Martin et al. (2015)

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)

Nuclear physics input

Erler et al. (2012)

nuclear masses, beta decay, reaction rates (neutron capture), fission

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

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)

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)

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)

Two neutron separation energy: abundances

freeze-out abundances before decay

Martin, Arcones, Nazarewicz, Olsen (2016)

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)

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)

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