Using failed supernovae to constrain the Galactic r-process element production. Issue 2 (16th May 2019)

• Record Type: Journal Article
• Authors: Wehmeyer, B; Fröhlich, C; Côté, B; Pignatari, M; Thielemann, F-K
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 487:Issue 2(2019)
• Page Start: 1745
• Page End: 1753
• Publication Date: 2019-05-16
• Subjects: Galaxy: abundances -- Galaxy: evolution -- nuclear reactions, nucleosynthesis, abundances -- Supernovae: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz1310
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age–metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution [(20 pc) 3 /cell] inhomogeneous chemical evolution tool 'ICE' to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.