Cosmological Nucleosynthesis and Active-Sterile Neutrino ...
Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis
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Transcript of Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis
Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis
T1/2P
nS
nsng
Sinaia, 2012
Karl-Ludwig Kratz
Part II
Summary “waiting-point” model
“weak” r-process
“main” r-process (early primary process; SN-II?)
superposition of nn-components
(later secondary process; explosive shell burning?)
seed Fe (implies secondary process)
Kratz et al., Ap.J. 662 (2007)
…largely site-independent!T9 and nn constant;instantaneous freezeout
To recapitulate…
Importance of nuclear-structure input !
Now…
from historical, site-independent “waiting-point” approaches
to more recent core-collapse SN nucleosynthesis calculations
Second part
r-Process calculations with MHD-SN models
2012 … new “hot r-process topic” magnetohydrodynamic SNe … but, nothing learnt about nuclear-physics input ???
“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…”
“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…”
Ap.J. Letter 750 (2012)
Phys.Rev. C85 (2012)
In both cases FRDM masses have been used partly misleading conclusions
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)
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
• time evolution of temperature, matter density and neutron density
• extended freezeout phase
“best” nuclear-physics input (Mainz, LANL, Basel)
Three main parameters:
electron abundance Ye = Yp = 1 – Yn
radiation entropy S ~ T³/rexpansion speed vexp durations ta and tr
(Farouqi, PhD Mainz 2005)
The Basel – Mainz HEW model
• nuclear masses• β-decay properties• n-capture rates• fission properties
full dynamical network (extension of Basel model)
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
Baryonk
Baryonkmk
YSVk
YY
BSN
eExpSN
Seed
n
111
3
108
,parameters correlated
p
α
seed
Formation of r-process “seed”
Time evolution of temperature and densityof HEW bubble(Vexp=10,000 km/s)
extended “freeze-out” phase!
temperature
density
Recombination of protons and neutrons into α-particlesas functions of temperature and time
For T9 ≤ 7 α dominate;at T9 ≈ 5 p disappear, n survive, “seed“ nuclei emerge.
n
(Farouqi et al., 2009)
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 !
Parameters HEW model Y(Z)
αn
seed
Ye=0.45
No neutrons no n-capture r-process!
Nucleosynthesis components:
S ≤ 100; Yn/Yseed < 1charged-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
S=196
Process duration: 146 ms
S=261
Process duration: 327 ms
Pb
UTh
not yet enough
Abun
danc
e Y
full Nr, distribution superposition of “weighted” S-components
Ye S τ[ms]
0.49 290 4120.45 260 3270.41 235 213
Ye S τ[ms]
0.49 230 2340.45 195 1460.41 160 109
Reproduction of Nr,
Superposition of S-components with Ye=0.45; weighting according to Yseed
No exponential fit to Nr, !
Process duration [ms]Entropy S FRDM ETFSI-Q Remarks
150 54 57 A≈115 region180 209 116 top of A≈130 peak220 422 233 REE pygmy peak245 691 339 top of A≈195 peak260 1290 483 Th, U280 2280 710 fission recycling300 4310 1395 “ “
significant effect of “shell-quenching” below doubly-magic 132Sn
TTTT
TTTT
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) DS40 kB/Baryon
r-Process robustness due to neutron shell closures
Kratz, Farouqi, Ostrowski (2007)
Freezeout at A ≈ 130
Validity and duration of (n,g) ↔ (g,n) equilibriumSn(real) / Sn(n, g ) 1
freezeout
Validity and duration ofβ-flow equilibriumλeff(Z) x Y(Z) ≠ 0
(n, g )-equilibrium valid over 200 ms,independent of Z
freezeoutLocal equilibrium “blobs” withIncreasing Z, at different times
Definition of different freezeout phasesNeutron freezeout at 140 ms, T9 0.8, Yn/Yr = 1 130PdChemical freezeout at 200 ms, T9 0.7, Yn/Yr 10-2 130CdDynamical freezeout at 450 ms, T9 0.3, Yn/Yr 10-4 130In
For Ye≤0.470 full r-process, up to Th, U
For Ye0.490 still 3rd peak, but no Th, U
For Ye=0.498 still 2nd peak, but no REE
Superposition of HEW components 0.450 ≤ Ye ≤ 0.498
Farouqi et al. (2009)
“weighting” of r-ejecta according to mass predicted by HEW model: for Ye=0.400 ca. 5x10-4 M for Ye=0.498 ca. 10-6 M
„What helps…?“ low Ye, high S, high Vexp
r-process observables
Solar system isotopic Nr, “residuals”
T9=1.35; nn=1020 - 1028
r-Process observables today
Pb,Bi
Observational instrumentation
• meteoritic and overall solar-system abundances
• ground- and satellite-based telescopes like Imaging Spectrograph (STIS) at Hubble, HIRES at Keck, and SUBARU
• recent „Himmelsdurchmusterungen“ HERES and SEGUE
Elemental abundances in UMP halo starBD+17°3248
Detection of 33 n-capture elements, the most in any halo star
Observations I: Selected “r-enriched” UMP halo stars
Sneden, Cowan & GallinoARA&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.
Halo stars vs. HEW-model: Extremes “r-rich” and “r-poor”
Eu
Eu
Factor 25 difference for Sr - Zr region !
g g
gg
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
r-poor “Honda star”
10 ≤ S ≤ 220incomplete main r-process
35% Nr,(Eu)
r-rich “Sneden star”
140 ≤ S ≤ 300
100% Nr,(Eu)
full main r-process
Extremes “r-rich” and “r-poor”: S-range optimized
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)
Sr – Cd region overabundant by a mean factor ≈ 8 relative to SS-r
“missing” part to SS-r = LEPP
Halo stars vs. HEW-model: Y/Eu and La/Eu
(I. Roederer et al., 2010; K. Farouqi et al., 2010)
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
Clear correlation between “r-enrichment” and Ye
Caution!La always 100 % scaled solar; log(La/Eu) trend correlated withsub-solar Eu in “r-poor” stars
“… the Ge abundances…track their Fe abundances very well.An explosive process on iron peak nuclei (e.g. the a-rich freezeout inSNe), rather than neutron capture,appears to have been the dominantmechanism for this element…”
“Ge abundance seen completelyuncorrelated with Eu”
Ap.J., 627 (2005)
solar abundance ra
tio
Ge – Eu corre
lation
Zr – Eu co
rrelation
Correlation between the abundance ratios of [Zr/Fe] (obtained exclusivley with HST STIS) and [Eu/Fe]. The dashed line indicates a direct correlation betweenZr and Eu abundances.
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 forCS 22892-052. The solid green line at [Ge/Fe]= -0.79is a fit to the observed data. A typical error is indicated by the cross.
Relative abundances [Ge/H] displayed as a function [Fe/H] metallicity for our sample of 11 Galactic halo stars. The arrowrepresents 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.
Observations: Correlation Ge, Zr with r-process?
Can our HEW modelexplain observations ?
“Zr abundances also do not vary cleanly with Eu”
Ge okay! 100% CPRZr two components?
ELEMENT Y(Z) as fct. of S in %20 ≤ S ≤ 100 100 ≤ S ≤ 160 160 ≤ S ≤ 280
38Sr 98 2.2 0.2
39Y 98 2.2 0.2
40Zr 82 18 0.3
46Pd 3.6 82 14
47Ag 0.6 77 23
52Te 0.001 10 90
56Ba - - 100
HEW with Ye =0.45; vexp =7500
CP componentuncorrelated
weak-r componentweakly correlated
main-r componentstrongly correlated
n-rich α-freezeoutnormal α -rich freezeout
with Eu ?
Relative elemental abundances, Y(Z)
From Sr via Pd, Ag to Ba different nucleosynthesis modes
Halo stars vs. HEW model: Sr/Y/Zr as fct. of [Fe/H], [Eu/H] and [Sr/H]
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) ?
–— HEW model (S ≥ 10); Farouqi (2009) – – average halo stars; Mashonkina (2009)
Zr in r-poor stars overabundant type “Honda star”Zr in halo & r-rich stars underabundant type “Sneden star”
Halo, r-rich and r-poor stars are clearly separated!
Halo stars vs. HEW model: Zr/Fe/Eu vs. [Eu/Fe], [Fe/H] and [Eu/H]
SS
Mashonkina (2009); Farouqi (2009)
Strong Zr – Eu correlationSS diagonal
HEW (av.)
r-poor
r-rich
Zr – Eu co
rrelation
Cowan et al. (2005)
similar metallicity different r- enrichment
ELEMENT Y(Z) as fct. of S in %20 ≤ S ≤ 100 100 ≤ S ≤ 160 160 ≤ S ≤ 280
38Sr 98 2.2 0.2
39Y 98 2.2 0.2
40Zr 82 18 0.3
46Pd 3.6 82 14
47Ag 0.6 77 23
52Te 0.001 10 90
56Ba - - 100
HEW with Ye =0.45; vexp =7500
CP componentuncorrelated
weak-r componentweakly correlated
main-r componentstrongly correlated
n-rich α-freezeoutnormal α -rich freezeout
with Eu ?
Relative elemental abundances, Y(Z)
From Sr via Pd, Ag to Ba different nucleosynthesis modes
Halo stars vs. HEW-model predictions: Pd
average Halo stars -1.5 < [Eu/H] < -0.6 log(Pd/Sr) - 0.95(0.09)
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”)
r-poor stars ([Eu/H] < -3) indicate TWO nucleosynthesis components for 46Pd: Pd/Sr uncorrelated, Pd/Eu (weakly) correlated with “main” r-process
Pd relation to CP-element Sr
Pd relation to r-element Eu
Pd/Sr and Pd/Eu different from Sr/Y/Zr
Observations of Pd & Ag in giant and dwarf stars
C. Hansen et al.; A&A in print (2012)
indication of different production processes (Sr – charged-particle, Ag – weak-r, Eu – main r-process)
anticorrelation between Ag and Sr anticorrelation between Ag and Eu
correlation of Pd and Ag
Pd and Ag are produced in the same process (predominantly) weak r-process
All observations in agreement with our HEW predictions !
CS31082
CS22892
Observations: [Ag/Fe] vs. [Eu/Fe]
BD+17°3248
HD221170
HD186478
HD108577
HD88609
HD122563
“r-poor” “r-rich”
Selection of pure r-process stars; no measurable s-process “contamination”
SAGA data base: [X/Fe] vs. [Eu/Fe] (I)
Zn Sr
Zr
SS SS
SSSS
r-poor r-rich
Transition from CP-component to “weak” n-capture r-process
Ag
Th
SAGA data base: [X/Fe] vs. [Eu/Fe] (II)
m1
Ir
m1
Dy
m1
SS
…Th – U – Pb cosmochronology ?!
The SS A ≈ 130 r-peak
r-Process observables today
Observational instrumentation
• meteoritic and overall solar-system abundances
• ground- and satellite-based telescopes like Imaging Spectrograph (STIS) at Hubble, HIRES at Keck, and SUBARU
• recent „Himmelsdurchmusterungen“ HERES and SEGUE
From elemental abundances to isotopic yields …;More sensitive to nuclear physics input, here in the 120 < A < 140 regionXe-H shows strong depletion of lighter isotopes with s-only 128, 130Xe “zero”.
r-process observables
Xe in nanodiamond stardust (I)
(U. Ott)
Xe in nanodiamond stardust (II)
(U. Ott)
(U. Ott)
Xe in nanodiamond stardust (III)
The “neutron-burst“ model (I)
The “neutron-burst” modelis 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 stars first ideas by Cameron Howard et al.; Meteoritics 27 (1992) Rauscher et al.; Ap.J. 576 (2002)
Several steps:1) start with SOLAR isotope distribution2) exposure to weak neutron fluence (t = 0.02 mbarn-1)
mimics weak s-processing during pre-SN phase3) s-ashes heated suddenly to T9 = 1.0 by SN shock4) 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-exposure 0.077 mbarn-1
shift of post-processed isotope pattern towards higher A
strong time and temperature dependence
Howard‘s Xe-H abundances N* are pure, unmixed yields;in addition, arbitrary mix with 5.5 parts Nּס => N-H
N-H = (N* + 5.5Nּס)/5.5N 0.182 + 1 = ּס N*/Nּס
N-H = 1 s-only 128,130Xe totally eliminated
…however,“there is little physical reasonto admix N* with solar abun-dances,other than the tradition ofinterpreting isotopic anomaliesas a binary admixture with SSabundances.“
arbitrary Nּס-mixing somewhat too strong!
The “neutron-burst“ model (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”
Xe in SN-II
The A 130 SS r-abundance peak
HEW reproduction of the solar-system A 130 r-abundance peak
Nuclear-physics input: ETFSI-Q; updated QRPA(GT+ff); experimental data
Ye = 0.45
“cold” r-processVexp = 20000; S(top) 140peak top at A 126
“hybrid” r-processVexp = 7500; S(top) 195peak top at 128 < A < 130
“hot” r-processVexp = 1000; S(top) 350peak top at A 136as, e.g. in Arcones & Martinez-Pinedo, Phys. Rev. C83 (2011)
Successive “cuts“ of low-S components
exclusion of “weak“ r-process
“strong“ r-process !
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 %
Experiment: T1/2 = 68 ms; Pn = 3.4 %
Surprising b-decay properties of 131Cd
QRPA predictions: T1/2(GT) = 943 ms;
Pn(GT) = 99 %
T1/2(GT+ff) = 59 ms;
Pn(GT+ff) = 14 %
Remember: …just ONE neutron outside N=82 magic shell
Nuclear-structure requests: higher Qβ, lower main-GT, low-lying ff-strength “new” nuclear-physics input for A ≈ 130 peak region
…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
Xe-H – HEW “new“
“new“ nuclear physics inputoptimized to measured T1/2, Pn and decayschemes 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
128 130 132 134 136Mass number A
0.0
0.5
1.0
1.5
2.0
i Xe/
136 X
e
Xe-HHEW total SHEW S>190HEW S>200HEW S>210
128 130 132 134 136Mass number A
0.0
0.5
1.0
1.5
2.0
i Xe/
136 X
e
128 130 132 134 136Mass number A
0.0
0.5
1.0
1.5
2.0
i Xe/
136 X
e
128 130 132 134 136Mass number A
0.0
0.5
1.0
1.5
2.0
i Xe/
136 X
e
128 130 132 134 136Mass number A
0.0
0.5
1.0
1.5
2.0
i Xe/
136 X
e
…same HEW r-process conditions as Xe-H !
towards Rauscher & Nʘ L'09
towards HEW
Pt-H in nanodiamonds
… at the end, an easy case for HEW SN-II “cold“ r-process !recent AMS measurement by Wallner et al.
Summary
Still today• there is no selfconsistent hydro-model for SNe, that provides the necessary
astrophysical conditions for a full r-process
• 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
Therefore,
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)
Main collaborators:
Discussion
???
Neutron star mergers
Pn effects at the A≈130 peak
Significant differences
(1) 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)
Halo stars vs. HEW model: “LEPP” elements
HEW (10 < S < 280)WP (Fe seed; 1020 < nn < 1028)weak-r (Si seed; nn 1018)
LEPP-abundances vs. CP- enrichment (Zr)
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)
Th/U – a robust and reliable r-process chronometer?
Neutron-density range [n/cm3]
r-C
hron
omet
er a
ge [G
yr]
norm.13.2 ± 2.8
Th/U robust – yesreliable – no
(not always)
Correlate Th, U with other elements, e.g. 3rd peak, Pb !
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:1) agreement Th/U and Th/Pb with NLTE analysis of Frebel-star (HE 1523-0901; [Fe/H] ≈ -3)2) 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.
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
at A=195 peak slow freezeout significant effect
T-dependent NON-SMOKER rates; ETFSI-Q + AME2003