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Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis

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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Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis

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  1. Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis Part II T1/2 sng Sn Pn  Karl-Ludwig Kratz Sinaia, 2012

  2. 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)

  3. Second part Now… from historical, site-independent “waiting-point” approaches to more recent core-collapse SN nucleosynthesis calculations

  4. 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…”

  5. 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)

  6. 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)

  7. 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

  8. 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)

  9. 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 !

  10. 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

  11. 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

  12. 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, !

  13. 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)

  14. 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

  15. 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)

  16. 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

  17. 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.

  18. 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 !

  19. 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

  20. 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)

  21. 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?

  22. 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 ?

  23. 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) ?

  24. 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)

  25. 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 ?

  26. 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

  27. 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)

  28. 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”

  29. 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

  30. SAGA data base: [X/Fe] vs. [Eu/Fe] (II) Ir Dy SS m1 m1 Th m1 …Th – U – Pb cosmochronology ?!

  31. 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”.

  32. Xe in nanodiamond stardust (I) (U. Ott)

  33. Xe in nanodiamond stardust (II) (U. Ott)

  34. Xe in nanodiamond stardust (III) (U. Ott)

  35. 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

  36. 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!

  37. 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”

  38. 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

  39. 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 !

  40. 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

  41. 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

  42. 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 !

  43. 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

  44. 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)

  45. Discussion

  46. Neutron star mergers ???

  47. 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)

  48. 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)

  49. 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 !

  50. 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.

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