The R-Process Alliance: On J0010−1735, an Accreted, Chemically Unusual, Metal-poor Star with R-process Enhancement
Abstract
We present a detailed chemo-dynamical analysis of the chemically peculiar very metal-poor ([Fe/H]=−2.22± 0.11) Milky Way (MW) halo star, 2MASS J00101758−1735387 (hereafter J0010-1735), discovered by the R-Process Alliance. We derive abundances for 45 elements, including 28 neutron-capture elements, and confirm that \thestar\ is highly r-process-enhanced, with [Eu/Fe]=+1.30. The light, α, and Fe-peak element abundances ratios relative to Fe are all sub-solar, aside from C, Si, and most extremely, Ca. We investigate three possible formation scenarios based on the star's chemical abundances and orbital kinematics: whether it formed in the \textit{in-situ} MW halo, in a MW dwarf galaxy satellite, or in a satellite of the Magellanic Cloud system. Using the position of \thestar\ in the [Mg/Mn]--[Al/Fe] plane, the abundance pattern of both the light and heavy elements, and the kinematics, we conclude that J0010-1735 most plausibly originated in a now-disrupted ultra-faint dwarf galaxy that was accreted into the MW halo. We examine potential chemical enrichment scenarios of J0010-1735, including one similar to the r-process-enhanced UFD Reticulum II, or enrichment via a sub-Chandrasekhar Type Ia SNe, potentially supplemented by a Ca-rich gap transient and by a separate neutron-rich site that facilitated r-process enrichment. A nuclear cosmochronometric age of 12.5±4.2 Gyr is derived from the [Th/Eu] ratio, consistent with an ancient origin in one of the earliest star-forming systems in the universe.
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BibTeX
@misc{hackshaw2026rprocess,
title = {{The $R$-Process Alliance: On J0010$-$1735, an Accreted, Chemically Unusual, Metal-poor Star with $R$-process Enhancement}},
author = {Zoe Hackshaw and Rana Ezzeddine and Shivani P. Shah and Terese T. Hansen and Ruijie Shi and Yangyang Li and Timothy C. Beers and Anna Frebel and Erika Holmbeck and Alexander P. Ji and Jeremy Kowkabany and Vinicius M. Placco and Ian U. Roederer and Charli M. Sakari},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.14987},
eprint = {2610.14987},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.14987},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The R-Process Alliance: On J0010−1735, an Accreted, Chemically Unusual, Metal-poor Star with R-process Enhancement
AU - Zoe Hackshaw
AU - Rana Ezzeddine
AU - Shivani P. Shah
AU - Terese T. Hansen
AU - Ruijie Shi
AU - Yangyang Li
AU - Timothy C. Beers
AU - Anna Frebel
AU - Erika Holmbeck
AU - Alexander P. Ji
AU - Jeremy Kowkabany
AU - Vinicius M. Placco
AU - Ian U. Roederer
AU - Charli M. Sakari
PY - 2026
DA - 2026/10/10
PB - arXiv
DO - 10.48550/arxiv.2610.14987
UR - https://arxiv.org/abs/2610.14987
AB - We present a detailed chemo-dynamical analysis of the chemically peculiar very metal-poor ([Fe/H]=−2.22± 0.11) Milky Way (MW) halo star, 2MASS J00101758−1735387 (hereafter J0010-1735), discovered by the R-Process Alliance. We derive abundances for 45 elements, including 28 neutron-capture elements, and confirm that \thestar\ is highly r-process-enhanced, with [Eu/Fe]=+1.30. The light, α, and Fe-peak element abundances ratios relative to Fe are all sub-solar, aside from C, Si, and most extremely, Ca. We investigate three possible formation scenarios based on the star's chemical abundances and orbital kinematics: whether it formed in the \textit{in-situ} MW halo, in a MW dwarf galaxy satellite, or in a satellite of the Magellanic Cloud system. Using the position of \thestar\ in the [Mg/Mn]--[Al/Fe] plane, the abundance pattern of both the light and heavy elements, and the kinematics, we conclude that J0010-1735 most plausibly originated in a now-disrupted ultra-faint dwarf galaxy that was accreted into the MW halo. We examine potential chemical enrichment scenarios of J0010-1735, including one similar to the r-process-enhanced UFD Reticulum II, or enrichment via a sub-Chandrasekhar Type Ia SNe, potentially supplemented by a Ca-rich gap transient and by a separate neutron-rich site that facilitated r-process enrichment. A nuclear cosmochronometric age of 12.5±4.2 Gyr is derived from the [Th/Eu] ratio, consistent with an ancient origin in one of the earliest star-forming systems in the universe.
ER -