Snapshots of r-process production in the Milky Way disk
Abstract
Stars enhanced in heavy neutron capture elements like europium (Eu) provide a window into the rarest and most exotic nucleosynthetic events. Most Eu-enhanced stars discovered thus far are found among metal-poor populations, with [Fe/H]<−1.0. Here, we report the discovery of $17$ vetted Eu-enhanced stars ([Eu/Fe]>0.7) in the Milky Way disk with metallicities in the range −0.87<[Fe/H]<−0.21 identified from among 74 717 stars in the GALAH survey. 14 of these stars additionally have [Ba/Eu]<0, marking enhancement from the rapid neutron capture (r-) process and making these r-II stars. Included in their number is a star with a remarkably high [Eu/H]=1.01±0.09 at [Fe/H]=−0.21. In addition to Eu, all 17 stars show enhancements in other neutron capture elements, especially in Nd, while otherwise appearing chemically consistent with typical disk stars, particularly in their α-element abundances. Two of the Eu-enhanced stars exhibit indications of binarity with strong enrichment in Ba and Y, marking potential signatures of the slow or intermediate neutron capture processes. This sample of 17 Eu-enhanced stars, which span both the high- and low-α disks, are valuable tracers of neutron capture processes, including the r-process, at high metallicities. Although we use criteria for Eu-enhanced stars typically applied to the halo to enable comparison to literature studies of r-process enhanced stars, we propose a new, metallicity-dependent selection for Eu enhancement that is better-suited to the regime of the Galactic disk.
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BibTeX
@misc{kane2026snapshots,
title = {{Snapshots of r-process production in the Milky Way disk}},
author = {Sarah G. Kane and Stephanie Monty and Madeleine McKenzie and HanYuan Zhang and Sven Buder and Terese Hansen and Tadafumi Matsuno and Jason Sanders and Anke Ardern-Arentsen and Vasily Belokurov and Zofia Kaczmarek and Andrew Garner},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.36013},
eprint = {2609.36013},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.36013},
}
RIS
TY - UNPB
TI - Snapshots of r-process production in the Milky Way disk
AU - Sarah G. Kane
AU - Stephanie Monty
AU - Madeleine McKenzie
AU - HanYuan Zhang
AU - Sven Buder
AU - Terese Hansen
AU - Tadafumi Matsuno
AU - Jason Sanders
AU - Anke Ardern-Arentsen
AU - Vasily Belokurov
AU - Zofia Kaczmarek
AU - Andrew Garner
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.36013
UR - https://arxiv.org/abs/2609.36013
AB - Stars enhanced in heavy neutron capture elements like europium (Eu) provide a window into the rarest and most exotic nucleosynthetic events. Most Eu-enhanced stars discovered thus far are found among metal-poor populations, with [Fe/H]<−1.0. Here, we report the discovery of $17$ vetted Eu-enhanced stars ([Eu/Fe]>0.7) in the Milky Way disk with metallicities in the range −0.87<[Fe/H]<−0.21 identified from among 74 717 stars in the GALAH survey. 14 of these stars additionally have [Ba/Eu]<0, marking enhancement from the rapid neutron capture (r-) process and making these r-II stars. Included in their number is a star with a remarkably high [Eu/H]=1.01±0.09 at [Fe/H]=−0.21. In addition to Eu, all 17 stars show enhancements in other neutron capture elements, especially in Nd, while otherwise appearing chemically consistent with typical disk stars, particularly in their α-element abundances. Two of the Eu-enhanced stars exhibit indications of binarity with strong enrichment in Ba and Y, marking potential signatures of the slow or intermediate neutron capture processes. This sample of 17 Eu-enhanced stars, which span both the high- and low-α disks, are valuable tracers of neutron capture processes, including the r-process, at high metallicities. Although we use criteria for Eu-enhanced stars typically applied to the halo to enable comparison to literature studies of r-process enhanced stars, we propose a new, metallicity-dependent selection for Eu enhancement that is better-suited to the regime of the Galactic disk.
ER -