Nucleosynthesis of Intermediate- Mass and Heavy Nuclei Friedrich-Karl Thielemann Department of Physics and Astronomy University of Basel with many collaborators over the years Basel: T. Rauscher, M. Liebendörfer, S. Rosswog, C. Freiburghaus, F. Brach-witz, C. Fröhlich, D. Mocelj Darmstadt: G. Martinez-Pinedo, K. Langanke,.. Mainz: K.-L. Kratz, B. Pfeiffer, K. Farouqi Oak Ridge: R. Hix,.. Nucleosynthesis of intermediate-mass and heavy nuclei ● Nucleosynthesis Processes after B2FH ● Stellar Burning and Final Stages ● Explosive Burning ● Equilibria and Freeze-out Effects ● Astrophysical Sites ● Existing Problems ● New Processes Required? Stellar Burning Stages Stellar Burning Stages Stellar Burning Stages Global Chemical (=Nuclear Statistical) Equilibrium (NSE) Explosive Burning Ne C Ne Si typical explosive burning process timescale order of seconds: fusion reactions (He, C, O) density dependent (He quadratic, C,O linear) photodisintegrations (Ne, Si) not density dependent Explosive Si-Burning 5 Explosive Burning above a critical temperature destroys (photodisintegrates) all nuclei and (re-)builds them up during the expansion. Dependent on density, the full NSE is maintained and leads to only Fe-group nuclei (normal freeze-out) or the reactions linking 4He to C and beyond freeze out earlier (alpha-rich freeze-out). Explosive Si-burning initially only 28Si, fully burned, finally alpha- rich freeze-out visualization: B.S. Meyer Quasi-Equilibrium (QSE) full NSE is not attained, but there exist equilibrium groups around 28Si, 56Ni and n,p,4He, which are separated by slow reactions Sample Calculations from ● B.S. Meyer and ● Hix and Thielemann alpha-rich freeze-out increasing entropy increasing entropy Thielemann et al. (1996) alpha-rich freeze-out occurs at high temperatures and/or low densities and is a function of entropy S in radiation-dominated matter ● it leads to the enhancement of “alpha-elements” ● and also to the extension of the Fe-group to higher masses (56Ni to 64Ge and for very high entropies up to A=80) “Historical” Present Understanding Burning Processes ● H-Burning (B2FH) ● He-Burning ● H-Burning ● expl. C, Ne, O-Burning, incomplete Si-Burning ● He-Burning ● explosive Si-Burning - about 70% normal freeze-out with ● alpha-Process Ye=0.42-47, about 30% alpha-rich freeze-out with Ye=0.5 ● e-Process ● s-Process (core and shell He-burning, ● s-Process neutrons from alpha-induced reactions on 22 Ne and 13C) ● r-Process ● r-Process (see below) ● p-Process (see below) ● p-Process ● x-Process (light elements D, Li, Be, B [big bang, cosmic ray spallation and ● x-Process neutrino nucleosynthesis]) The Heavy Elements Solar abundances (Anders & Grevesse) (from Anders & Grevesse) s-process r-process p-process s-, r- and p-Process F. Käppeler P. Möller p-Process (explosive Ne-burning = “photon spallation”) Arnould and Goriely (2003)problems in underproducing Mo, Ru and a number of heavier p- process isotopes!! Working of the r-Process ● (complete) Explosive Si-Burning ● 1. (very) high entropy alpha-rich (charged-particle) freeze-out with upper equilibrium extending up to A=80 - quasi-equilibria in isotopic chains (chemical quilibrium for neutron captures and photodisintegrations) with maxima at specific neutron separation energies Sn - neutron/seed(A=80) ratio and Sn of r-process path dependent on entropy and Ye ● 2. low entropies and normal freeze-out with very low Ye, leading also to large n/seed ratios - Sn function of Ye n/seed ratios as function of S and Ye Freiburghaus et al. (1999) nn=1020 r-Process paths for nn=1020, 1023 and 1026 K.-L. Kratz 82 84 86 88 90 92 94 Ba Cs Xe I Te Sb Sn In Cd Ag Pd Rh Ru Tc Mo Nb Zr nn=1023 Y Sr Rb Kr Br As Se n =10n 26 Ge Ga Zn Cu Ni Co Fe 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 Z N „waiting-point“ isotopes for nn=1020, 1023 and1026 Individual Superpositions of Entropy Components Farouqi (2005), above S=270-280 fission back-cycling sets in Pb Th U Processes in the Nuclear Chart H. Schatz Astrophysical Sites Hertzsprung-Russell Diagram of Stellar Evol-ution from Iben, showing as end stages ● white dwarfs and ● (core collapse) supernovae main sequence Type Ia Supernovae from Accretion in Binary Stellar Systems Back of the Envelope SN Ia P. Höflich Neutronization via electron capture (high Fermi energies at central densities) 56 Ni 54 Fe, 58Ni 56 Fe 50 Ti,54Cr (a) Test for influence of new shell model electron capture rates (LMP) (b) Test for burning front propagation speed Ignition density determines Ye and neutron-richness of (60-70% of) Fe-group results of explosive C, Ne, O and Si- burning: Fe-group to alpha- elements 2/1-3/1 SNe Ia dominate Fe-group, over- abundances by more than factor 2 not permitted central density <4 109 gcm-3 Future 3D Models Travaglio, Reinecke, Hillebrandt, Thielemann (2004) hydrodynamic instabilities determine propagation of burning consistent treatment needed instead of parametrized spherical propagation, MPA Garching, U. Chicago, U. Texas/Florida Role of Sne Ia and Sne II in galactic evolution stellar surface abundances as witness of gas composition during formation Prantzos (2005) [el/Fe] onset of Sne Ia at [Fe/H]=-1 dominate Fe-production, alpha- elements dominated by Sne II. Core Collapse Supernovae from Massive Stars Neutrino-driven Core Collapse Supernovae A. Mezzacappa “Faking” multi-D hydro with neutrinos We make use of 1D models and Liebendörfer et al. (2004) reduction factors on neutrino code AGILE/BOLTZTRAN scattering or enlargement factors in with full Boltzmann neutrino neutrino absorption in order to obtain transport typical explosion energies Nucleosynthesis problems in “induced” piston or thermal bomb models utilized up to present to obtain explosive nucleosynthesis yields with induced explosion energies of 1051 erg prior results of Thielemann, Nomoto, Woosley, Chieffi .. made use of initial stellar structure (and Ye!) when inducing artificial explosion. This neglects the effect of the explosion mechanism on the innermost zones, causes strange overproductions of Ni isotopes and does not go mucch beyond Ni! In exploding models matter in innermost ejected zones becomes proton-rich (Ye>0.5) if the neutrino flux is sufficiant (scales with 1/r2)! : Fröhlich et al. (2006a) A: neutrino scattering cross sections scaled (%) B: neutrino absorption cross sections scaled (factor) Improved Fe-group composition Models with Ye>0.5 lead to an alpha-rich freeze-out with remaining protons which can be captured similar to an rp- process. This ends at 64Ge, due to (low) densities and a long beta-decay half-life (decaying to 64Zn). This effect improves the Fe- group composition in general and extends it to Cu and Zn! Fröhlich et al. (2006a) νp-process A new process, which could solve some Fröhlich et al. (2006b); observational problems of Sr, Y, Zr in early also strong overabundances can galactic evolution and the problem of light p- be obtained up to Sr and beyond process nuclei. (light p-process nuclei) Anti-neutrino capture on protons provides always a small background of neutrons which can mimic beta-decay via (n,p)-reactions. Variations in explosion dynamics and neutrino luminosity Fröhlich et al. (2006b), see also Pruet et al. (2006) permits to explain on the one hand that in some cases only large overabundances of Sr are found, on the other hand early abundances of Sr,Y, Zr as well as possible p-process nuclei up to A=120 Observations of Sr, Y, Zr in low- metallicity stars Travaglio et al. (2004) Frebel et al. (2005) large variations in Sr between different low-metallicity stars Need for early Sr,Y,Zr before onset of s-process Observational Constraints on r-Process Sites Cowan and Sneden “rare” event, which must be related apparently uniform abundances above to massive stars due to “early” Z=56 (and up to Z=82?) -> “unique” appearance at low astrophysical event which nevertheless metallicities(behaves similar to SN consists of a superposition of ejected II products like O, but with much mass zones larger scatter) What is the site of the r-process? from S. Rosswog from H.-T. Janka NS Mergers, problems: ejection SN neutrino wind, problems: too late in galactic evolution high enough entropies attained? Superposition of 5 entropies N=50 N=82 N=126 Th, U r-process chronometers „weak“ r-process Thesis K. Farouqi 2005: entropies up to about 280, higher entropies lead to fission back- cycling! Low (high) entropies produce essentially an alpha-rich freeze-out around A=80 without neutrons left and leave abundance features which do not fit the A=80 peak. However from meteorites as well as low metallicity stars we know that another process (weak r-process) must be responsible here. Finding high entropies seemed extremely difficilt in neutrino wind (Thompson et al. 2001)! Only very massive neutron stars seemed to come close to conditions (entropies) which can produce the third peak!!! Fission Cycling in Neutron Star Mergers Freiburghaus et al. (1999) with simplified symmetric fission for nuclei with A>250, complete lack of nuclei below A=115 Self-consistent explosion models absolutely needed! fallback onto neutron increasing explosion star: supernova and energy: neutron star black hole and supernova Liebendörfer et al. direct black (2006), explosions hole formation via changed neu- trino properties only with models which provide the explosion energy and the properties of the innermost ejected matter we can give a clear prediction of the Fe-group composition and possible r-process ejecta. Most recent models of the Garching, Arizona, Los Alamos and Basel groups (in 2D) see apparently high enough entropies for the r-process in the fall back.
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