{
  "abstract": "We characterize in 3I/ATLAS the heliocentric evolution of the CN production rate and the forbidden [OI] emission, describe the broader emission line inventory, and release the analysis tools and reduced data products to the community. We obtained high-resolution spectroscopy of 3I/ATLAS with VLT/ESPRESSO ($r_{\\rm h}\\!=\\!1.67\\!-\\!2.45$ au). The CN production rates were derived by fitting the $B^2Σ^+\\!-\\!X^2Σ^+$ band using CometSpec, a publicly released Python package for flexible fluorescence modeling. The three forbidden [OI] lines were modeled to derive the green-to-red (G/R) flux ratio and a $\\rm CO_2 / H_2O$ proxy. We fit $\\text{Q}_{\\rm CN}=a\\,(r_{\\rm h}/1\\text{ au})^{\\,b}$ to the production rate versus heliocentric distance relation. The pre-perihelion CN power-law index is $b_{\\rm pre}\\!=\\!-4.62^{+1.25}_{-1.22}$, which is within the range observed for Solar System comets. The CN residuals about the smooth model show substantial scatter that we attribute to a combination of systematics and possible physical drivers that the current cadence cannot disentangle. The G/R ratio decreases from $\\sim\\!0.42\\!\\pm\\!0.14$ at $r_{\\rm h}\\!\\simeq\\!2.4$ au to $\\sim\\!0.114\\!\\pm\\!0.004$ near perihelion. The $\\rm CO_2 / H_2O$ proxy spans $\\sim 0.06 - 1.06$ and is comparable to the values reported by Subaru/HDS and SPHEREx and to those measured for 2I/Borisov. We additionally identify NiI and FeI and report post-perihelion production rates for $\\rm C_2$ and CH. Our high-resolution monitoring of 3I/ATLAS reveals a $\\rm CO_2$-rich coma that becomes progressively $\\rm H_2O$-dominated near perihelion. Together with the public release of CometSpec and the reduced data, these results provide an empirical reference and a methodological framework for the next generation of interstellar object monitoring campaigns.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: A&A, 713, A251 (2026)",
  "arxiv": "2607.15355",
  "author_total": 5,
  "authors": [
    {
      "name": "Baltasar Luco"
    },
    {
      "name": "Thomas H. Puzia"
    },
    {
      "name": "Rohan Rahatgaonkar"
    },
    {
      "name": "Juan Pablo Carvajal"
    },
    {
      "name": "Prasanta K. Nayak"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9qpvg7sp3r8nw.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2607.15355",
  "fulltext_url": null,
  "id": "9qpvg7sp3r8nw",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2607.15355",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2607.15355",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-07",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9qpvg7sp3r8nw.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:37Z",
      "native_id": "2607.15355",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2607.15355"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO",
  "title_text": "Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:37Z",
  "url": "https://research.draconitic.com/paper/9qpvg7sp3r8nw",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1051/0004-6361/202660647",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}