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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:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [1]
  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:
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

Citation Formats

Holmbeck, Erika M., Frebel, Anna, McLaughlin, G. C., Mumpower, Matthew R., Sprouse, Trevor M., and Surman, Rebecca. Actinide-rich and Actinide-poor r -process-enhanced Metal-poor Stars Do Not Require Separate r -process Progenitors. United States: N. p., 2019. Web. doi:10.3847/1538-4357/ab2a01.
Holmbeck, Erika M., Frebel, Anna, McLaughlin, G. C., Mumpower, Matthew R., Sprouse, Trevor M., & Surman, Rebecca. Actinide-rich and Actinide-poor r -process-enhanced Metal-poor Stars Do Not Require Separate r -process Progenitors. United States. doi:10.3847/1538-4357/ab2a01.
Holmbeck, Erika M., Frebel, Anna, McLaughlin, G. C., Mumpower, Matthew R., Sprouse, Trevor M., and Surman, Rebecca. Tue . "Actinide-rich and Actinide-poor r -process-enhanced Metal-poor Stars Do Not Require Separate r -process Progenitors". United States. doi:10.3847/1538-4357/ab2a01.
@article{osti_1565905,
title = {Actinide-rich and Actinide-poor r -process-enhanced Metal-poor Stars Do Not Require Separate r -process Progenitors},
author = {Holmbeck, Erika M. and Frebel, Anna and McLaughlin, G. C. and Mumpower, Matthew R. and Sprouse, Trevor M. and Surman, Rebecca},
abstractNote = {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.},
doi = {10.3847/1538-4357/ab2a01},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 881,
place = {United States},
year = {2019},
month = {8}
}

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