{
  "abstract": "The origin of the heaviest elements remains a fundamental mystery, with the \"actinide-boost\" (Thorium overabundance) serving as a critical diagnostic of r-process nucleosynthesis conditions. While this diversity is well documented in extremely metal-poor (EMP) stars, its frequency in the mildly metal-poor (MMP) regime ($-2.0 < $ [Fe/H] $< -0.5$) is poorly constrained due to blending issues in the commonly used 4019 angstrom line. We present a systematic abundance analysis of mildly metal-poor stars, exploiting the relatively unblended Th II 5989 angstrom line. High-dispersion spectra were obtained using the 1.5 m telescope at Gunma Astronomical Observatory with GAOES, complemented by archival data from the Subaru Telescope/HDS retrieved via SMOKA. We successfully detected Th in 32 out of 42 sample stars. Our analysis demonstrates that the 5989 angstrom line is a useful diagnostic for Th abundance measurements in cool red giants. The mean [Th/Eu] ratio remains nearly constant over the MMP metallicity range, suggesting that progressive homogenization of the interstellar medium during Galactic chemical evolution would reduce abundance variations inherited from individual r-process events, or the dominant r-process events may share similar initial Th/Eu production ratios. While the [Th/Eu] ratio is nearly constant overall in the MMP regime, its dispersion appears to increase toward the metal-rich end of this regime and reaches approximately 1 dex near solar metallicity. This behavior may reflect the combined effects of variations in the initial Th/Eu production ratios of the progenitor objects, the mixing of r-process products in the interstellar medium, and the radioactive decay of Th over stellar lifetimes.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.13880",
  "author_total": 2,
  "authors": [
    {
      "name": "Kurumi Furutsuka"
    },
    {
      "name": "Satoshi Honda"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/a14mqajddmqq6.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.13880",
  "fulltext_url": null,
  "id": "a14mqajddmqq6",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.13880",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7213350984",
  "pdf_url": "https://arxiv.org/pdf/2609.13880",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-12",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/a14mqajddmqq6.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.13880",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.13880"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "Investigating r-Process Diversity in Mildly Metal-Poor Stars Using the Th II 5989 Angstrom Line",
  "title_text": "Investigating r-Process Diversity in Mildly Metal-Poor Stars Using the Th II 5989 Angstrom Line",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/a14mqajddmqq6",
  "venue": "arXiv",
  "versions": []
}