The $R$-Process Alliance: Actinide Abundances, Variation, and Evolution in Metal-Poor Stars
Fuente:
arXiv
Enregistré dans:
| Auteurs principaux: | , , , , , , , , , , , , , |
|---|---|
| Format: | Preprint |
| Publié: |
2026
|
| Sujets: | |
| Accès en ligne: | |
| Tags: |
Ajouter un tag
Pas de tags, Soyez le premier à ajouter un tag!
|
| _version_ | 1866914472338128896 |
|---|---|
| author | Shah, Shivani P. Ezzeddine, Rana Holmbeck, Erika M. Ji, Alexander P. Placco, Vinicius M. Roederer, Ian U. Mardini, Mohammad K. Usman, Sam A. Bandyopadhyay, Avrajit Beers, Timothy C. Frebel, Anna Hansen, Terese T. Sakari, Charli M. Sneden, Chris |
| author_facet | Shah, Shivani P. Ezzeddine, Rana Holmbeck, Erika M. Ji, Alexander P. Placco, Vinicius M. Roederer, Ian U. Mardini, Mohammad K. Usman, Sam A. Bandyopadhyay, Avrajit Beers, Timothy C. Frebel, Anna Hansen, Terese T. Sakari, Charli M. Sneden, Chris |
| contents | The actinides, including thorium (Th), are the heaviest observable elements synthesized in the universe, holding clues to the extremes of the astrophysical and nuclear conditions of $r$-process sites. We present Th abundances based on high-resolution spectroscopy for 47 metal-poor stars, the largest homogeneously analyzed sample to date. The chemical evolution of Th exhibits a decrease in dispersion in [Th/H] and [Th/Fe] from $\sim$0.6 dex at the lowest metallicities to $\sim$0.2 dex at higher metallicities. We also find that Th and the lanthanides Eu and Dy are co-produced remarkably well, with average [Th/Eu]$\sim0.0$ across $-3.0 \lesssim$ [Fe/H] $\lesssim -1.5$, as well as across stars with $0.0\lesssim$ [Eu/Fe] $\lesssim2.5$. Even so, the absolute range of $\logε$(Th/Eu) is 1.02 dex, with an observed standard deviation of $\pm0.20$ dex and an intrinsic standard deviation of $\pm0.11$ dex at the lowest metallicities. We infer that $68\%$ of $r$-process events have $\logε$(Th/Eu) yields that only vary within a factor of $\pm1.3$ or $\pm30\%$, while $5\%$ of $r$-process events have $\logε$(Th/Eu) yields that vary by factors $>3.3$ approaching $\sim$10. This serves as a strong constraint for the nuclear and astrophysical models of $r$-process sites, and suggests that achieving an $r$-process site that is both prompt and produces a robust $\logε$(Th/Eu) ratio is a challenge for current models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_12892 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The $R$-Process Alliance: Actinide Abundances, Variation, and Evolution in Metal-Poor Stars Shah, Shivani P. Ezzeddine, Rana Holmbeck, Erika M. Ji, Alexander P. Placco, Vinicius M. Roederer, Ian U. Mardini, Mohammad K. Usman, Sam A. Bandyopadhyay, Avrajit Beers, Timothy C. Frebel, Anna Hansen, Terese T. Sakari, Charli M. Sneden, Chris Solar and Stellar Astrophysics Astrophysics of Galaxies The actinides, including thorium (Th), are the heaviest observable elements synthesized in the universe, holding clues to the extremes of the astrophysical and nuclear conditions of $r$-process sites. We present Th abundances based on high-resolution spectroscopy for 47 metal-poor stars, the largest homogeneously analyzed sample to date. The chemical evolution of Th exhibits a decrease in dispersion in [Th/H] and [Th/Fe] from $\sim$0.6 dex at the lowest metallicities to $\sim$0.2 dex at higher metallicities. We also find that Th and the lanthanides Eu and Dy are co-produced remarkably well, with average [Th/Eu]$\sim0.0$ across $-3.0 \lesssim$ [Fe/H] $\lesssim -1.5$, as well as across stars with $0.0\lesssim$ [Eu/Fe] $\lesssim2.5$. Even so, the absolute range of $\logε$(Th/Eu) is 1.02 dex, with an observed standard deviation of $\pm0.20$ dex and an intrinsic standard deviation of $\pm0.11$ dex at the lowest metallicities. We infer that $68\%$ of $r$-process events have $\logε$(Th/Eu) yields that only vary within a factor of $\pm1.3$ or $\pm30\%$, while $5\%$ of $r$-process events have $\logε$(Th/Eu) yields that vary by factors $>3.3$ approaching $\sim$10. This serves as a strong constraint for the nuclear and astrophysical models of $r$-process sites, and suggests that achieving an $r$-process site that is both prompt and produces a robust $\logε$(Th/Eu) ratio is a challenge for current models. |
| title | The $R$-Process Alliance: Actinide Abundances, Variation, and Evolution in Metal-Poor Stars |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2604.12892 |