Collapsar R-process Yields Can Reproduce [Eu/Fe] Abundance Scatter in Metal-poor Stars

• Published in: The Astrophysical journal Vol. 915; no. 2; pp. 81 - 93
• Main Authors: Brauer, Kaley, Ji, Alexander P., Drout, Maria R., Frebel, Anna
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-07-2021; IOP Publishing
• Subjects: Accretion disks; Astronomy & Astrophysics; Astrophysics; Black holes; Bursts; Collapsars; Collapse; Core-collapse supernovae; Europium; Iron; Luminosity; Massive stars; Metallicity; Metals; Neutron stars; Nucleosynthesis; R-process; Scattering; Star mergers; Stellar abundances; Stellar evolution; Stellar jets; Stellar rotation; Supernovae; Yield
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac00b2

Abstract
It is unclear if neutron star mergers can explain the observed
r
-process abundances of metal-poor stars. Collapsars, defined here as rotating massive stars whose collapse results in a rapidly accreting disk around a black hole that can launch jets, are a promising alternative. We find that we can produce a self-consistent model in which a population of collapsars with stochastic europium yields synthesizes all of the
r
-process material in metal-poor ([Fe/H] < − 2.5) stars. Our model reproduces the observed scatter and evolution of scatter of [Eu/Fe] abundances. We find that if collapsars are the dominant
r
-process site for metal-poor stars,
r
-process synthesis may be linked to supernovae that produce long
γ
-ray bursts. Our results also allow for the possibility that core-collapse supernovae beyond those that launch
γ
-ray bursts also produce
r
-process material (e.g., potentially a subset of Type Ic-BL supernovae). Furthermore, we identify collapsar jet properties (isotropic energy, engine luminosity, or engine time) that may trace
r
-process yield and verify that the amount of
r
-process yield produced per collapsar in our model ( ∼ 0.07
M
⊙
) is consistent with other independent estimates. In the future, achieving 0.05 dex precision on distribution scatter or a reliable selection function would further constrain our probe of
r
-process production. Our model would also hold for another prompt
r
-process site with a power-law yield, and work is needed to determine if, for example, fast-merging neutron stars can also explain abundance scatter.