Kaori Otsuki

University of Chicago

Astrophysical site for the r-process


The investigation of elements formed by rapid neutron-capture process (the r-process) is an important focus in current astronomy and astrophysics. Although those elements are believed to be formed in explosive environments like type II supernovae, the astrophysical sites for the r-processes is still unknown. It has been reported that the ratio of heavy neutron-capture elements (e.g., Ba, Eu) to light neutron-capture elements (e.g., Y, Zr, Sr) in metal deficient stars shows scatter. The scatter could be explained by two different processes; one forms both of light r-process elements and heavy elements (i.e., main r-process) and another forms only light elements without increasing heavy elements (i.e., weak r-process). We calculated r-process nucleosynthesis in three measure candidate for the main r-process,
(1) neutrino-driven winds in Type II SNe (e.g., Otsuki et al. 2000),
(2) prompt explosion of light SNe (e.g., Wanajo et al. 2003),
(3) neutron star mergers (e.g., Freiboughaus et al. 1999), with same nuclear physics model.
We will discuss if it is possible to constrain the astrophysical site for the r-process from their abundance distributions. We found we need to clarify (1) weak r-process contributions (2) nuclear physics uncertainties (especially fission), to distinguish r-process nucleosynthesis in those three environments. Effects of neutron-capture of light elements (Z>10) (Terasawa et al. 2001) and di-neutron capture of 4He for each environments were also studied. The neutron-capture of light elements affects final abundance distribution of all three environments, but the effect of di-neutron capture is significant only in neutron-star merger calculations. In addition, fission cycle may hide both effects in the case of neutron star mergers.

Back to the Astrophysics at Argonne page.