The r-Process: History, Required Conditions, Astrophysical Sites, and Observations

Abstract

This review of the rapid-neutron-capture (i.e. r-) process starts with determining the Solar System r-abundance pattern via first obtaining (and subtracting) the contribution from the slow-neutron capture (s-) process. We emphasize the extensive work in this area by our late colleague Roberto Gallino and continue in an overview, concentrating on attempts to reproduce the solar r-process pattern with historical site-independent approaches, based on nuclear physics far from stability. In a second step we address the existing proposals for astrophysical sites. Among stellar observations we start with available observations of individual events before analyzing low-metallicity stars, which witness r-process contributions in the early Galaxy. We conclude with a comparison of observations and model predictions, focusing on our present ability to identify the responsible individual astrophysical sites by their imprint in Galactic evolution.

This is an invited review for the special issue of The European Physical Journal A, titled "About Stars and Nuclei: Honoring the Legacy of Roberto Gallino". This is the final accepted version, but written in "Astronomy Style" (i.e. with named references rather than numbered references as in the EPJA)