A simple model for r-process scatter and halo evolution

Brian D. Fields, James W. Truran, John J. Cowan

Research output: Contribution to journalArticlepeer-review


Recent halo-star observations of heavy elements produced by rapid neutron capture (r-process) show a striking behavior: within a single star, the relative abundances of r-process elements heavier than Ba are the same as those of solar system matter, while across stars with similar metallicity Fe/H, the r/Fe ratio varies by more than 2 orders of magnitude. In this paper we present a simple analytic model that describes a star's abundances in terms of its "ancestry," i.e., the number of nucleosynthesis events (e.g., supernova explosions) that contributed to the star's composition. This model leads to a very simple analytic expression for the abundance scatter versus Fe/H, which is in good agreement with the data and with more sophisticated numerical models. We investigate two classes of scenarios for r-process nucleosynthesis, one in which r-process synthesis events occur in only ∼4% of supernovae but iron synthesis is ubiquitous, and one in which iron nucleosynthesis occurs in only about 9% of supernovae (the Wasserburg-Qian model). We find that the predictions in these scenarios are similar for [Fe/H] ≳ - 2.5, but that these models can be readily distinguished observationally by measuring the dispersion in r/Fe at [Fe/H] ≲ - 3.

Original languageEnglish (US)
Pages (from-to)845-854
Number of pages10
JournalAstrophysical Journal
Issue number2 I
StatePublished - Aug 20 2002


  • Galaxy: abundances
  • Nuclear reactions, nucleosynthesis, abundances
  • Stars: abundances

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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