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Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis. Part II. T 1/2. s n g. S n. P n. . Karl-Ludwig Kratz. Sinaia, 2012. Summary “waiting-point” model. To recapitulate…. seed Fe (implies secondary process). superposition of n n -components.

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slide1

Astrophysical, observational and nuclear-physics

aspects of r-process nucleosynthesis

Part II

T1/2

sng

Sn

Pn

Karl-Ludwig Kratz

Sinaia, 2012

slide2

Summary “waiting-point” model

To recapitulate…

seed Fe (implies secondary process)

superposition of nn-components

…largely site-independent!

T9 and nn constant;

instantaneous freezeout

Importance of nuclear-structure input !

“weak” r-process

(later secondary process;

explosive shell burning?)

“main” r-process

(early primary process; SN-II?)

Kratz et al., Ap.J. 662 (2007)

slide3

Second part

Now…

from historical, site-independent “waiting-point” approaches

to more recent core-collapse SN nucleosynthesis calculations

slide4

r-Process calculations with MHD-SN models

2012 … new “hot r-process topic” magnetohydrodynamic SNe

… but, nothing learnt about nuclear-physics input ???

Phys.Rev. C85 (2012)

“We investigate the effect of newly measured ß-decayhalf-lives on r-process nucleosynthesis. We adopt … a magnetohydrodynamic supernova explosion model…

The (T1/2) effect slightly alleviates, but does not fullyexplain, the tendency of r-process models to underpro-duce isotopes with A = 110 – 120…”

In both cases FRDM masses have been usedpartly misleading conclusions

Ap.J. Letter 750 (2012)

“We examine magnetohydrodynamically driven SNe

as sources of r-process elements in the early Galaxy…

… the formation of bipolar jets could naturally providea site for the strong r-process…”

slide5

The high-entropy / neutrino-driven wind model

Nevertheless, cc-SN “HEW”…still one of the presently favoured scenarios for a rapid neutron-capture nucleosynthesis process

The neutrino-driven wind starts from

the surface of the proto-neutron starwith a flux of neutrons and protons.

As the nucleons cool (≈10 ≥ T9 ≥ 6),

they combine to α-particles + an

excess of unbound neutrons.

Further cooling (6 ≥ T9 ≥ 3) leads to the

formation of a few Fe-group "seed"nuclei in the so-called α-rich freezeout.

Still further cooling (3 ≥ T9 ≥ 1) leads to

neutron captures on this seed compo-

sition, making the heavy r-process

nuclei.

(Woosley & Janka, Nature, 2005)

slide6

The Basel – Mainz HEW model

full dynamical network(extension of Basel model)

  • time evolution of temperature, matter density and neutron density
  • extended freezeout phase
  • “best” nuclear-physics input(Mainz, LANL, Basel)
  • nuclear masses
  • β-decay properties
  • n-capture rates
  • fission properties

Threemain parameters:

electron abundanceYe= Yp = 1 – Yn

radiation entropy S ~ T³/r

expansion speed vexp durations taand tr

(Farouqi, PhD Mainz 2005)

slide7

First results of dynamical r-process calculations

  • Conditions for successful r-process
  • „strength“ formula
  • Neutron-rich r-process seed beyond N=50 (94Kr, 100Sr, 95Rb…)
  •  avoids first bottle-neck in classical model
  • Initial r-process path at particle freezeout (T9 3)
  •  Yn/Yseed ≤ 150
  • Total process duration up to Th, U
  • τr ≤ 750 ms
  • instead of  3500 ms in classical model
  • Due to improved nuclear-physics input (e.g. N=82 shell quenching!)
  • max. S  280
  • to form full 3rd peak and Th, U
  • Freezeout effects (late non-equilibrium phase)
  • capture of “free” neutrons
  •  recapture of bdn-neutrons

parameters correlated

slide8

Formation of r-process “seed”

temperature

Time evolution of

temperature and density

of HEW bubble

(Vexp=10,000 km/s)

 extended “freeze-out” phase!

density

Recombination of protons

and neutrons

into α-particles

as functions of temperature and time

For T9 ≤ 7 α dominate;

at T9 ≈ 5  p disappear,

n survive,

“seed“ nuclei emerge.

α

n

p

seed

(Farouqi et al., 2009)

slide9

Distribution of seed nuclei

effect of different expansion velocities

of the hot bubble, Vexp

distributions are robust !

effect of different electron

abundances, Ye

distributions show differences,

mainly for A > 100

Main seed abundances at A > 80 lie beyond N = 50 !

slide10

Parameters HEW model  Y(Z)

Ye=0.45

α

n

No neutrons no n-capture r-process!

seed

Nucleosynthesis components:

S ≤ 100; Yn/Yseed < 1

charged-particle process

100 < S < 150; 1 < Yn/Yseed< 15

“weak” r-process

150 < S < 300; 15 < Yn/Yseed< 150

“main” r-process

synthesizing the a 130 and a 195 peaks
Synthesizing the A=130 and A=195 peaks

S=196

S=261

Process duration: 146 ms

Process duration: 327 ms

not yet enough

Pb

Abundance Y

Th

U

full Nr, distribution  superposition of “weighted” S-components

slide12

Process duration [ms]

Entropy S FRDMETFSI-Q Remarks

  • 54 57 A≈115 region
  • 209 116 top of A≈130 peak
  • 422 233 REE pygmy peak
  • 691339top of A≈195 peak
  • 1290 483 Th, U
  • 2280 710 fission recycling
  • 300 4310 1395 “ “

significant effect of

“shell-quenching”

below doubly-magic

132Sn

Reproduction of Nr,

Superposition of S-components with Ye=0.45;

weightingaccording to Yseed

T

T

T

T

T

T

T

T

No exponential fit to Nr, !

slide13

r-Process robustness due to neutron shell closures

Width of A=130 and 195 peaks ca. 15 m.u.;

width of REE pygmy peak ca. 50 m.u.;

Widths of all three peaks (A=130, REE

and A=195) DS40 kB/Baryon

Kratz, Farouqi, Ostrowski (2007)

slide14

Freezeout at A ≈ 130

Validity and duration of

(n,g) ↔ (g,n) equilibrium

Sn(real) / Sn(n,g )  1

Validity and duration of

β-flow equilibrium

λeff(Z) x Y(Z) ≠ 0

freezeout

freezeout

Local equilibrium “blobs” with

Increasing Z, at different times

(n, g )-equilibrium valid over  200 ms,

independent of Z

Definition of different freezeout phases

Neutron freezeout at  140 ms, T9  0.8, Yn/Yr = 1 130Pd

Chemical freezeout at  200 ms, T9  0.7, Yn/Yr  10-2 130Cd

Dynamical freezeout at  450 ms, T9  0.3, Yn/Yr 10-4 130In

slide15

Superposition of HEW components 0.450 ≤ Ye ≤ 0.498

“weighting” of r-ejecta according to mass predicted by HEW model:

for Ye=0.400 ca. 5x10-4 M

for Ye=0.498 ca. 10-6M

For Ye≤0.470

full r-process,

up to Th, U

For Ye0.490

still 3rd peak,

but no Th, U

For Ye=0.498

still 2nd peak,

but no REE

„What helps…?“ low Ye, high S, high Vexp

Farouqi et al. (2009)

slide16

r-Process observables today

Solar system isotopic Nr, “residuals”

  • Observationalinstrumentation
  • meteoriticandoverallsolar-system
  • abundances
  • ground- andsatellite-basedtelescopeslikeImaging Spectrograph (STIS) atHubble, HIRESatKeck, andSUBARU
  • recent„Himmelsdurchmusterungen“
  • HERES and SEGUE

T9=1.35; nn=1020 - 1028

Pb,Bi

r-process observables

Elemental abundances in UMP halo star

BD+17°3248

Detection of 33 n-capture elements, the most in any halo star

slide17

Observations I: Selected “r-enriched” UMP halo stars

Sneden, Cowan & Gallino

ARA&A, 2008

Same abundance pattern at the upper end and ??? at the lower end

  • Two options for HEW-fits to UMP halo-star abundances:
          • const. Ye = 0.45, optimize S-range;
          • optimize Ye with corresponding full S-range.
slide18

Halo stars vs. HEW-model: Extremes “r-rich” and “r-poor”

Elemental abundance ratios UMP halo stars

r-rich “Cayrel star” / r-rich “Sneden star”

r-poor “Honda star” / r-rich “Sneden star”

normalized to Eu

g

g

Eu

Eu

g

g

Factor 25 difference for Sr - Zr region !

slide19

Extremes “r-rich” and “r-poor”: S-range optimized

r-rich “Sneden star”

full main r-process

140 ≤ S ≤ 300

Sr – Cd region underabundant by a mean factor ≈ 2 relative to SS-r

(assumption by Travaglio et al. that this pattern is unique for all UMP halo stars)

“missing” part to SS-r = LEPP

100% Nr,(Eu)

r-poor “Honda star”

10 ≤ S ≤ 220

incomplete main r-process

35% Nr,(Eu)

Sr – Cd region overabundant by a mean factor ≈ 8relative to SS-r

slide20

Halo stars vs. HEW-model: Y/Eu and La/Eu

Instead of restriction to a single Ye with different S-ranges,

probably more realistic, choice of different Ye’s with corresponding full S-ranges

39Y represents charged-particle component

(historical “weak” n-capture

r-process)

57La represents“main”r-process

Caution!

La always 100 % scaled solar; log(La/Eu) trend correlated withsub-solar Eu in “r-poor” stars

Clear correlation between “r-enrichment” and Ye

(I. Roederer et al., 2010; K. Farouqi et al., 2010)

slide21

Observations: Correlation Ge, Zr with r-process?

Ap.J., 627 (2005)

“Zr abundances also do not vary cleanly with Eu”

Zr – Eu correlation

solar abundance ratio

“Ge abundance seen completely

uncorrelated with Eu”

Relative abundances [Ge/H] displayed as a function [Fe/H]

metallicity for our sample of 11 Galactic halo stars. The arrow

represents the derived upper limit for CS 22892-052. The

dashed line indicates the solar abundance ratio of these

elements: [Ge/H] = [Fe/H], while the solid green line shows

the derived correlation [Ge/H]=[Fe/H]= -0.79. A typical error

is indicated by the cross.

Correlation between the abundance ratios of [Zr/Fe]

(obtained exclusivley with HST STIS) and [Eu/Fe].

The dashed line indicates a direct correlation between

Zr and Eu abundances.

Ge – Eu correlation

Can our HEW model

explain observations ?

“… the Ge abundances…

track their Fe abundances very well.

An explosive process on iron peak

nuclei (e.g. the a-rich freezeout in

SNe), rather than neutron capture,

appears to have been the dominant

mechanism for this element…”

Correlation between the abundance ratios [Ge/Fe] and

[Eu/Fe]. The dashed line indicates a direct correlation

between Ge and Eu abundances. As in the previous

Figure, the arrow represents the derived upper limit for

CS 22892-052. The solid green line at [Ge/Fe]= -0.79

is a fit to the observed data. A typical error is indicated

by the cross.

Ge okay! 100% CPR

Zr two components?

slide22

Relative elementalabundances, Y(Z)

From Sr via Pd, Ag to Ba

different nucleosynthesis modes

HEW with Ye =0.45; vexp =7500

normal α -rich freezeout

n-rich α-freezeout

CP component

uncorrelated

weak-r component

weakly correlated

main-r component

strongly correlated

with Eu ?

slide23

Halo stars vs. HEW model: Sr/Y/Zr as fct. of [Fe/H], [Eu/H] and [Sr/H]

–— HEW model (S ≥ 10); Farouqi (2009)

– –average halo stars; Mashonkina (2009)

Robust Sr/Y/Zr abundance ratios,

independent of metallicity,

r-enrichment,

α-enrichment.

Same nucleosynthesis component:

CP-process, NOT n-capture r-process

Correlation with main r-process (Eu) ?

slide24

SS

Halo stars vs. HEW model: Zr/Fe/Eu vs. [Eu/Fe], [Fe/H] and [Eu/H]

Cowan et al. (2005)

Zr in r-poor stars overabundant

type “Honda star”

Zr in halo & r-rich stars underabundant

type “Sneden star”

Zr – Eu correlation

Strong Zr – Eucorrelation

SS diagonal

Halo, r-rich and r-poor stars

are clearly separated!

r-poor

HEW (av.)

r-rich

different r- enrichment

similar metallicity

Mashonkina (2009); Farouqi (2009)

slide25

Relative elementalabundances, Y(Z)

From Sr via Pd, Ag to Ba

different nucleosynthesis modes

HEW with Ye =0.45; vexp =7500

normal α -rich freezeout

n-rich α-freezeout

CP component

uncorrelated

weak-r component

weakly correlated

main-r component

strongly correlated

with Eu ?

slide26

Halo stars vs. HEW-model predictions: Pd

Pd/Sr and Pd/Eu different from Sr/Y/Zr

average Halo stars

-1.5 < [Eu/H] < -0.6

log(Pd/Sr)  - 0.95(0.09)

Pd relation to CP-element Sr

HEW model

log(Pd/Sr) = - 0.81 (“r-rich”)

- 1.16(“r-poor”)

average Halo stars

-1.5 < [Eu/H] < -0.6

log(Pd/Eu)  +0.81(0.07)

HEW model

log(Pd/Eu) = +1.25 (Pd CP+r)

+0.89(“r-rich”)

+1.45 (”r-poor”)

Pd relation to r-element Eu

r-poor stars ([Eu/H] < -3) indicate TWO nucleosynthesis components for 46Pd:

Pd/Sr  uncorrelated, Pd/Eu  (weakly) correlated with “main” r-process

slide27

Observations of Pd & Ag in giant and dwarf stars

anticorrelation between Ag and Sr

anticorrelation between Ag and Eu

indication of different production processes

(Sr – charged-particle, Ag – weak-r, Eu – main r-process)

Pd and Ag are produced in the

same process

(predominantly) weak r-process

All observationsin agreement with our HEW predictions!

correlation of Pd and Ag

C. Hansen et al.; A&A in print (2012)

slide28

Observations: [Ag/Fe] vs. [Eu/Fe]

Selection of pure r-process stars; no measurable s-process “contamination”

CS31082

CS22892

BD+17°3248

HD221170

HD108577

HD186478

HD88609

HD122563

“r-poor”

“r-rich”

slide29

SAGA data base: [X/Fe] vs. [Eu/Fe] (I)

Transition from CP-component to “weak” n-capture r-process

Zn

Sr

SS

SS

r-poor

r-rich

Zr

SS

Ag

SS

slide30

SAGA data base: [X/Fe] vs. [Eu/Fe] (II)

Ir

Dy

SS

m1

m1

Th

m1

…Th – U – Pb cosmochronology ?!

slide31

r-Process observables today

The SS A ≈ 130 r-peak

  • Observationalinstrumentation
  • meteoriticandoverallsolar-system
  • abundances
  • ground- andsatellite-basedtelescopeslikeImaging Spectrograph (STIS) atHubble, HIRESatKeck, andSUBARU
  • recent„Himmelsdurchmusterungen“
  • HERES and SEGUE

r-process observables

Fromelementalabundancesto isotopic yields …;More sensitive to nuclear physics input, here in the 120 < A < 140 region

Xe-H shows strong depletion of lighter isotopes with s-only 128, 130Xe “zero”.

slide35

The “neutron-burst“ model (I)

The “neutron-burst” model

is the favored nucleosynthesis scenario in the cosmochemistry community;

so far applied to isotopic abundances of Zr, Mo, Ru, Te, Xe, Ba, Pt

Historical basis:…neutron burst in shocked He-rich matter in exploding massive starsfirst ideas by Cameron Howard et al.; Meteoritics 27 (1992) Rauscher et al.; Ap.J. 576 (2002)

  • Several steps:
    • start withSOLAR isotope distribution
    • exposure to weak neutron fluence (t = 0.02 mbarn-1)
    • mimics weak s-processing during pre-SN phase
    • s-ashes heated suddenly to T9 = 1.0 by SN shock
    • expansion and cooling on 10 s hydrodynamical timescale
    • resulting n-density (from (a,n)-reactions) during burst ≈ 1017 n/cm3
    • for ≈ 1 s final n-exposure0.077 mbarn-1

shift of post-processed isotope pattern towards higher A

strong time and temperature dependence

slide36

The “neutron-burst“ model (II)

Howard‘s Xe-H abundances N* are pure, unmixed yields;

in addition, arbitrary mix with 5.5 parts Nסּ=> N-H

N-H = (N* + 5.5Nסּ)/5.5Nסּ = 1 + 0.182 N*/Nסּ

N-H = 1 s-only128,130Xe totally eliminated

…however,

“there is little physical reason

to admix N* with solar abun-

dances,

other than the tradition of

interpreting isotopic anomalies

as a binary admixture with SS

abundances.“

arbitrary Nסּ-mixing

somewhat too strong!

slide37

Xe in SN-II

Two SN models

a) site-independent “waiting-point“ approach

b) high-entropy-wind ejecta of core-collapse SN-II

  • full parameter space in
  • a) nn-components
  • b) S-ranges
  • No reproduction of Xe-H !
  • special variants of r-process?
  • “hot“
  • “cold“ r-process
  • “strong”
slide38

The A  130 SS r-abundance peak

HEW reproduction of the solar-system A  130 r-abundance peak

“cold” r-process

Vexp = 20000; S(top)  140

peak top atA  126

“hybrid” r-process

Vexp = 7500; S(top)  195

peak top at 128 < A < 130

“hot” r-process

Vexp = 1000; S(top)  350

peak top at A  136

Ye = 0.45

as, e.g. in Arcones & Martinez-Pinedo,

Phys. Rev. C83 (2011)

Nuclear-physics input:

ETFSI-Q; updated QRPA(GT+ff);

experimental data

slide39

Xe-H – HEW “old“

“old“ nuclear physics input

e.g. 129Ag T1/2(g.s.) = 46 ms;

130Pd T1/2 = 98 ms; P1-2n = 96 %; 4 %

Successive “cuts“ of low-S

components

exclusion of “weak“ r-process

“strong“ r-process !

slide40

Surprising b-decay properties of 131Cd

Remember: …just ONE neutron outside N=82 magic shell

Experiment: T1/2 = 68 ms; Pn = 3.4 %

QRPA predictions:

T1/2(GT) = 943 ms;

Pn(GT)= 99 %

T1/2(GT+ff) = 59 ms;

Pn(GT+ff)= 14 %

Nuclear-structure requests: higher Qβ, lower main-GT, low-lying ff-strength

“new” nuclear-physics input for A ≈ 130 peak region

slide41

Xe-H – HEW “new“

“new“ nuclear physics input

optimized to measured T1/2, Pn and decay

schemes of 130Cd and 131Cd

e.g. 129Ag stellar-T1/2 = 82 ms;

130Pd T1/2(new/old) ≈ 0.2; P1-2n(new/old) ≈ 0.8; 4.5

  • reduction of 129Xe
  • increase of 136Xe

…but, still „cuts“ of low-S region necessary

again, exclusion of “weak“ r-process

“strong“ r-process !

129Xe, 131Xe, 134Xe okay;132Xe still factor ≈ 2 too high

slide42

Pt-H in nanodiamonds

… at the end, an easy case for HEW SN-II “cold“ r-process !

recent AMS measurement by Wallner et al.

towards HEW

towards Rauscher & Nʘ L'09

…same HEW r-process conditions as Xe-H !

slide43

Summary

  • Still today
    • there is no selfconsistent hydro-model for SNe, that provides the necessary astrophysical conditions for a full r-process

Therefore,

  • parameterized dynamical studies (like our HEW approach) are still useful to explain r-process observables;
  • astronomical observations & HEW calculations indicate that SS-r and UMP halo-star abundance distributions are superpositions of 3 nucleosynthesis components: charged-particle, weak-r and main-r
  • the yields of the CP-component (up to Zr) are largely uncorrelated with the “main” r-process;
  • the yields of the weak-r component (Mo to Cd) are partly correlated with the “main” r-process; elements ≥ Te belong to the “main” r-process
  • HEW can explain the peculiar isotopic anomalies in SiC-X grains and nanodiamond stardust
slide44

Main collaborators:

K. Farouqi (Mainz)

B. Pfeiffer (Mainz & Gießen)

O. Hallmann (Mainz)

U. Ott (Mainz)

P. Möller (Los Alamos)

F.-K. Thielemann (Basel)

W.B. Walters (Maryland)

L.I. Mashonkina (RAS, Moscow)

C. Sneden & I. Roederer (Austin, Texas)

A. Frebel (MIT, Cambridge)

N. Christlieb (LSW, Heidelberg)

C.J. Hansen (LSW, Heidelberg)

slide47

Pn effects at the A≈130 peak

  • Significant differences
  • smoothing of odd-even Y(A)
  • staggering
  • (2) importance of individual
  • waiting-point nuclides,
  • e.g. 127Rh, 130Pd, 133Ag, 136Cd
  • (3) shift left wing of peak

in clear contrast to Arcones & Martinez-PinedoPhys. Rev. C83 (2011)

slide48

Halo stars vs. HEW model: “LEPP” elements

LEPP-abundances vs. CP- enrichment (Zr)

HEW (10 < S < 280)

WP (Fe seed; 1020 < nn < 1028)

weak-r (Si seed; nn 1018)

HEW reproduces high-Z LEPP observations (Sr – Sn);

underestimates low-Z LEPP observations (Cu – Ge)

additional nucleosynthesis processes ?

(e.g. Fröhlich et al. np-process;

Pignatari et al. rs-process;

El Eid et al. early s-process)

(Farouqi, Mashonkina et al. 2008)

slide49

Th/U – arobust and reliabler-process chronometer?

norm.

13.2 ± 2.8

r-Chronometer age [Gyr]

Neutron-density range [n/cm3]

Th/U robust – yes

reliable – no

(not always)

Correlate Th, U with other elements, e.g. 3rd peak, Pb !

slide50

How about Pb as r-chronometer ?

In principle, direct correlation of Pb to Th, U

≈ 85% abundance from α-decay from actinide region

Sensitivity to age:

Pb

0 Gyr Y(Pb) = 0.375 (Mainz) // Sneden et al. (2008) Y(Pb) = 0.622 ?

5 Gyr 0.433

13 Gyr 0.451

Th,U/Pb

13 Gyr: Th/Pb ≈ 0.048

U/Pb ≈ 0.007

  • New HEW results:
  • agreement Th/U and Th/Pb with NLTE analysis of Frebel-star (HE 1523-0901; [Fe/H] ≈ -3)
  • consistent picture for Th/Ba – Th/U for 4 “r-rich” halo-stars with Ye≈0.45;
  • and for the “actinide-boost” Cayrel-star with Ye≈ 0.44.
slide51

Effect of n-capture rates on A=130 and A=195 peaks

blue curve: <σv>

green curve: 1/100 x <σv>

red curve: 100 x <σv>

at A=130 peak fast freezeout

 no significant effect

T-dependent NON-SMOKER rates; ETFSI-Q + AME2003

at A=195 peak slow freezeout

 significant effect