Title: Actinide-rich and Actinide-poor r -process-enhanced Metal-poor Stars Do Not Require Separate r -process Progenitors

Abstract

The astrophysical production site of the heaviest elements in the universe remains a mystery. Incorporating heavy-element signatures of metal-poor, $r$-process-enhanced stars into theoretical studies of $r$-process production can offer crucial constraints on the origin of heavy elements. In this study, we introduce and apply the "actinide-dilution with matching" model to a variety of stellar groups, ranging from actinide-deficient to actinide-enhanced, to empirically characterize r-process ejecta mass as a function of electron fraction. We find that actinide-boost stars do not indicate the need for a unique and separate $r$-process progenitor. Rather, small variations of neutron richness within the same type of $r$-process event can account for all observed levels of actinide enhancements. The very low-$$Y_e$$ , fission-cycling ejecta of an $r$-process event need only constitute 10%–30% of the total ejecta mass to accommodate most actinide abundances of metal-poor stars. We find that our empirical $$Y_e$$ distributions of ejecta are similar to those inferred from studies of GW170817 mass ejecta ratios, which is consistent with neutron-star mergers being a source of the heavy elements in metal-poor, $r$-process-enhanced stars.

Authors:

Holmbeck, Erika M.  ^[1];

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Frebel, Anna  ^[2];

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McLaughlin, G. C.  ^[3];

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Mumpower, Matthew R.  ^[4];

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Sprouse, Trevor M.  ^[5];

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Surman, Rebecca  ^[1]

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+ Show Author Affiliations

1. Univ. of Notre Dame, IN (United States). Dept. of Physics; Joint Inst. for Nuclear Astrophysics (JINA), East Lansing, MI (United States)
2. Joint Inst. for Nuclear Astrophysics (JINA), East Lansing, MI (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Physics
3. Joint Inst. for Nuclear Astrophysics (JINA), East Lansing, MI (United States); North Carolina State Univ., Raleigh, NC (United States) Dept. of Physics
4. Joint Inst. for Nuclear Astrophysics (JINA), East Lansing, MI (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division
5. Univ. of Notre Dame, IN (United States). Dept. of Physics

Publication Date:

2019-08-06

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC). Nuclear Physics (NP) (SC-26)

OSTI Identifier:

1565905

Report Number(s):

LA-UR-19-23313
Journal ID: ISSN 1538-4357

Grant/Contract Number:  

89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 881; Journal Issue: 1; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; Atomic, Nuclear and Particle Physics; Astronomy and Astrophysics