Charged-particle and neutron-capture processes in the high-entropy wind of core-collapse supernovae

K. Farouqi, K.L. Kratz, B. Pfeiffer, T. Rauscher, Friedrich-Karl Thielemann, J. W. Truran

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Abstract

The astrophysical site of the r-process is still uncertain, and a full exploration of the systematics of this process in terms of its dependence on nuclear properties from stability to the neutron drip-line within realistic stellar environments has still to be undertaken. Sufficiently high neutron-to-seed ratios can only be obtained either in very neutron-rich low-entropy environments or moderately neutron-rich high-entropy environments, related to neutron star mergers (or jets of neutron star matter) and the high-entropy wind of core-collapse supernova explosions. As chemical evolution models seem to disfavor neutron star mergers, we focus here on high-entropy environments characterized by entropy S, electron abundance Y(e), and expansion velocity V(exp). We investigate the termination point of charged-particle reactions, and we define a maximum entropy S(final) for a given V(exp) and Y(e), beyond which the seed production of heavy elements fails due to the very small matter density. We then investigate whether an r-process subsequent to the charged-particle freeze-out can in principle be understood on the basis of the classical approach, which assumes a chemical equilibrium between neutron captures and photodisintegrations, possibly followed by a beta-flow equilibrium. In particular, we illustrate how long such a chemical equilibrium approximation holds, how the freeze-out from such conditions affects the abundance pattern, and which role the late capture of neutrons originating from beta-delayed neutron emission can play. Furthermore, we analyze the impact of nuclear properties from different theoretical mass models on the final abundances after these late freeze-out phases and beta-decays back to stability. As only a superposition of astrophysical conditions can provide a good fit to the solar r-abundances, the question remains how such superpositions are attained, resulting in the apparently robust r-process pattern observed in low metallicity stars.

Original languageEnglish
Pages (from-to)1359-1377
Number of pages19
JournalThe Astrophysical Journal
Volume712
Issue number2
DOIs
Publication statusPublished - 1 Apr 2010

Keywords

  • supernovae: general
  • STATISTICAL-MODEL CALCULATIONS
  • R-PROCESS NUCLEOSYNTHESIS
  • Sun: abundances
  • II SUPERNOVAE
  • PROCESS ABUNDANCES
  • nuclear reactions, nucleosynthesis, abundances
  • ASTROPHYSICAL REACTION-RATES
  • LOW-METALLICITY
  • NUCLEAR-MASS FORMULA
  • PROTONEUTRON STARS
  • DRIVEN WINDS
  • ALPHA-PROCESS

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