The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. Some of our models produce an abundance spike at A = 132 that is absent in the Solar system r-process distribution. Disc outflows reach the third peak (A ~ 195) in most of our simulations, although the amounts produced depend sensitively on the disc viscosity, initial mass or entropy of the torus, and nuclear physics inputs. This implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of r-process elements in metal poor stars.
We find that outflows produce a robust abundance pattern around the second r-process peak (mass number A ~ 130), independent of model parameters, with significant production of A more » < 130 nuclei. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important – and in some cases dominant – contribution to the total mass ejected by the merger. We consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star–black hole mergers.
Our result thus suggests that black-hole-torus winds from compact binary mergers have the potential to be a major, but probably not the dominant, production site of r-process elements. These produce qualitative agreement with observation when both black hole collapse and observational realities are taken into = for black-hole-torus winds from merger remnants to be the dominant source of the r-process elements. They test the tr-process hypothesis with calculations that are terminated before all r-process trajectories have been ejected.
The observed fraction of tr-process stars is found to be consistent with expectations from the initial mass function (IMF), and they suggest that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. they suggest that many such stars have begun an r-process, but it was prevented from running to completion in more massive stars by collapse to black holes, creating a 'truncated r-process,' or 'tr-process'. Nonetheless, a significant number of these stars do not share this r-process template. Nucleosynthesis of heavy nuclei in metal-poor stars is generally ascribed to the r-process, as the abundance pattern in many such stars agrees with the inferred Solar r-process abundances.
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