Thorium and Europium production in the early Galaxy: Implications for nucleocosmochronology

@misc{magrini2026thorium,
  title = {{Thorium and Europium production in the early Galaxy: Implications for nucleocosmochronology}},
  author = {L. Magrini and R. E. Giribaldi and M. Palla and S. Randich and L. Pasquini and C. J. Hansen and R. Smiljanic and M. Racca and M. Tsantaki and J. Schiappacasse-Ulloa and A. Skuladottir and G. Kordopatis and L. Berni and T. Matsuno and G. Casali and V. Hill and F. Matteucci and G. Cescutti and F. Rizzuti and E. Spitoni},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.07697},
  eprint = {2611.07697},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.07697},
}

TY  - UNPB
TI  - Thorium and Europium production in the early Galaxy: Implications for nucleocosmochronology
AU  - L. Magrini
AU  - R. E. Giribaldi
AU  - M. Palla
AU  - S. Randich
AU  - L. Pasquini
AU  - C. J. Hansen
AU  - R. Smiljanic
AU  - M. Racca
AU  - M. Tsantaki
AU  - J. Schiappacasse-Ulloa
AU  - A. Skuladottir
AU  - G. Kordopatis
AU  - L. Berni
AU  - T. Matsuno
AU  - G. Casali
AU  - V. Hill
AU  - F. Matteucci
AU  - G. Cescutti
AU  - F. Rizzuti
AU  - E. Spitoni
PY  - 2026
DA  - 2026/11/05
PB  - arXiv
DO  - 10.48550/arxiv.2611.07697
UR  - https://arxiv.org/abs/2611.07697
AB  - The ages of the oldest stellar populations can be investigated through nucleocosmochronology, with the thorium-to-europium abundance ratio providing a promising chronometer. We assess the reliability of log(Th/Eu) as an age indicator by testing whether thorium and europium were co-produced in a constant ratio in metal-poor stars, and evaluate the uncertainties affecting stellar ages. We present new Th and Eu abundance measurements for eight TITANS reference stars observed with UVES at the VLT. Combining these measurements with homogeneous literature samples, we investigate the behaviour of log(Th/Eu) as a function of metallicity. We derive ages adopting a theoretical initial r-process production ratio and assess the effects of observational uncertainties and sample statistics. At low metallicity, the observed Th/Eu ratios show no significant dependence on metallicity after excluding stars with anomalous actinide abundances, supporting broadly uniform Th and Eu co-production in the early Galaxy. The derived ages are consistent with expectations for an old, metal-poor halo population, although individual uncertainties remain substantial. Higher spectral resolution is needed to improve Th measurements, while combining stars in coeval populations can provide additional statistical gains. Nucleocosmochronology offers an independent approach to dating the oldest stellar populations. Homogeneous samples of coeval stars, particularly in globular clusters, observed with future high-resolution multi-object spectrographs could provide stronger constraints on the early formation history of the Milky Way and the age of the Universe.
ER  -