r-Process Contributions to Low-Metallicity Stars

¹ Dept. of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
² GSI Helmholtz Center for Heavy Ion Research, Planckstrasse 1, D-64291 Darmstadt, Germany
³ ZAH, Landessternwarte, University of Heidelberg, Königstuhl 12, D69117 Heidelberg, Germany
⁴ The Oskar Klein Centre, Department of Astronomy, Stockholm University, Stockholm, Sweden
⁵ Dept. of Chemistry, Pharmacy & Geosciences, University of Mainz, D-55126 Mainz, Germany
⁶ Max Planck Institute for Chemistry (Otto Hahn Institute), D-55128 Mainz, Germany

^* e-mail: f-k.thielemann@unibas.ch

Published online: 24 February 2022

Abstract

Various nucleosynthesis studies have pointed out that the rapid neutron capture r-process elements in very metal-poor (VMP) halo stars might have different origins. It has been known that an r-process can either be obtained in neutron-rich low Ye conditions or in high entropy environments [see e.g. 1–5], an overview over many investigations has appeared recently [6]. In the present article we analyze with statistical methods the observational abundance patterns from trans-Fe elements up to the actinides and come to the conclusion that four to five categories of astrophysical events must have contributed. These include the ejection of Fe and trans-Fe elements Sr, Y, Zr (continuing possibly beyond to slightly higher mass numbers) in category 0 events (hereafter "C0"), Fe and weak r-process contributions (including Eu in moderate to slightly larger but varying amounts) in CI and CII events, strong r-process abundance patterns with no or negligible (in comparison to solar) Fe production in CIIIa and CIIIb events, where category CIIIb shows a tendency for an actinide boost behavior. When comparing these categories with presently existing nucleosynthesis predictions, we suggest to identify them (despite remaining uncertainties) with regular core-collapse supernovae, quark deconfinement supernovae, magneto-rotational supernovae, neutron star mergers, and outflows from black hole accretion tori.