Friedrich -K. Thielemann

Publications (268) View all

• Article: Abundances of neutron-capture elements in stars of the galactic disk substructures

  T. V. Mishenina, M. Pignatari, S. A. Korotin, C. Soubiran, C. Charbonnel, F. -K. Thielemann, T. I. Gorbaneva, N. Yu. Basak
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  ABSTRACT: The aim of this work is to present and discuss the observations of the iron peak (Fe, Ni) and neutron-capture element (Y, Zr, Ba, La, Ce, Nd, Sm, and Eu) abundances for 276 FGK dwarfs, located in the galactic disk with metallicity -1 < [Fe/H] < +0.3. Atmospheric parameters and chemical composition of the studied stars were determined from an high resolution, high signal-to-noise echelle spectra obtained with the echelle spectrograph ELODIE at the Observatoire de Haute-Provence (France). Effective temperatures were estimated by the line depth ratio method and from the H_{\alpha} line-wing fitting. Surface gravities (log g) were determined by parallaxes and the ionization balance of iron. Abundance determinations were carried out using the LTE approach, taking the hyperfine structure for Eu into account, and the abundance of Ba was computed under the NLTE approximation. We are able to assign most of the stars in our sample to the substructures of the Galaxy thick disk, thin disk, or Hercules stream according to their kinematics. The classification of 27 stars is uncertain. For most of the stars in the sample, the abundances of neutron-capture elements have not been measured earlier. For all of them, we provide the chemical composition and discuss the contribution from different nucleosynthesis processes.
  03/2013;
• Source

  Available from: Nihal Buyukcizmeci

  Article: A comparative study of statistical models for nuclear equation of state of stellar matter

  N. Buyukcizmeci, A. S. Botvina, I. N. Mishustin, R. Ogul, M. Hempel, J. Schaffner-Bielich, F. -K. Thielemann, S. Furusawa, K. Sumiyoshi, S. Yamada, H. Suzuki
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  ABSTRACT: We compare three different statistical models for the equation of state (EOS) of stellar matter at subnuclear densities and temperatures (0.5-10 MeV) expected to occur during the collapse of massive stars and supernova explosions. The models introduce the distributions of various nuclear species in nuclear statistical equilibrium, but use somewhat different nuclear physics inputs. It is demonstrated that the basic thermodynamical quantities of stellar matter under these conditions are similar, except in the region of high densities and low temperatures. We demonstrate that mass and isotopic distributions have considerable differences related to the different assumptions of the models on properties of nuclei at these stellar conditions. Overall, the three models give similar trends, but the details reflect the uncertainties related to the modelling of medium effects, such as the temperature and density dependence of surface and bulk energies of heavy nuclei, and the nuclear shell structure effects. In order to establish a relationship between nuclear physics inputs for astrophysical calculations and the experimental data obtained from intermediate-energy nuclear reactions, we also discuss the similarities and differences of the conditions reached during supernova explosions and heavy-ion collisions.
  11/2012;
• Article: 44Ti, 26Al and 53Mn samples for nuclear astrophysics: the needs, the possibilities and the sources

  R Dressler, M Ayranov, D Bemmerer, M Bunka, Y Dai, C Lederer, Jennifer Fallis, StJ A Murphy, M Pignatari, D Schumann, T Stora, T Stowasser, F-K Thielemann, P J Woods
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  ABSTRACT: Exploration of the physics involved in the production of cosmogenic radionuclides requires experiments using the same rare, radioactive nuclei in sufficient quantities. For this work, such exotic radionuclides have been extracted from previously proton-irradiated stainless steel samples using wet chemistry separation techniques. The irradiated construction material has arisen from an extended material research programme at the Paul Scherrer Institute, called STIP (SINQ Target Irradiation Program), where several thousand samples of different materials were irradiated with protons and neutrons of energies up to 570 MeV. In total, 8 × 10^17 atoms of 44Ti, ∼10^16 atoms of 26Al and ∼10^19 atoms of 53Mn are available from selected samples. These materials may now be used to produce targets or radioactive beams for nuclear reaction studies with protons, neutrons and α-particles. The work is part of the ERAWAST initiative (Exotic Radionuclides from Accelerator Waste for Science and Technology), aimed at facilitating new collaborations between the isotope producers and users from different scientific fields including nuclear astrophysics.
  J. Phys G: Nucl. Part. Phys. 09/2012; 39(10):105201.
• Source

  Available from: Friedrich -K. Thielemann

  Article: Have Superheavy Elements been Produced in Nature?

  I. Petermann, K. Langanke, G. Martínez-Pinedo, I. V. Panov, P. -G. Reinhard, F. -K. Thielemann
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  ABSTRACT: We discuss the possibility whether superheavy elements can be produced in Nature by the astrophysical rapid neutron capture process. To this end we have performed fully dynamical network r-process calculations assuming an environment with neutron-to-seed ratio large enough to produce superheavy nuclei. Our calculations include two sets of nuclear masses and fission barriers and include all possible fission channels and the associated fission yield distributions. Our calculations produce superheavy nuclei with A ~ 300 that however decay on timescales of days.
  07/2012;
• Article: Neutrino-driven wind simulations and nucleosynthesis of heavy elements

  A. Arcones, F. -K. Thielemann
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  ABSTRACT: Neutrino-driven winds, which follow core-collapse supernova explosions, present a fascinating nuclear astrophysics problem that requires understanding advanced astrophysics simulations, the properties of matter and neutrino interactions under extreme conditions, the structure and reactions of exotic nuclei, and comparisons against forefront astronomical observations. The neutrino-driven wind has attracted vast attention over the last 20 years as it was suggested to be a candidate for the astrophysics site where half of the heavy elements are produced via the r-process. In this review, we summarize our present understanding of neutrino-driven winds from the dynamical and nucleosynthesis perspectives. Rapid progress has been made during recent years in understanding the wind with improved simulations and better micro physics. The current status of the fields is that hydrodynamical simulations do not reach the extreme conditions necessary for the r-process and the proton or neutron richness of the wind remains to be investigated in more detail. However, nucleosynthesis studies and observations point already to neutrino-driven winds to explain the origin of lighter heavy elements, such as Sr, Y, Zr.
  07/2012;