{
  "abstract": "We report the first detection of the neutral methyl radical CH ₃ in a highly evolved C-rich object, SMP LMC 011, using the Mid-Infrared Instrument (MIRI) Medium-Resolution Spectrometer (MRS) on JWST. CH ₃ is well fitted by an excitation temperature of T ex ≃ 190 K and a column density of N tot (CH ₃ ) ≃ 5.6 × 10 ¹⁷ cm ⁻² . We also report the nondetection of ethane (C ₂ H ₆ ), consistent with CH ₃ reacting preferentially with unsaturated radicals rather than self-recombination, which may be inefficient in SMP LMC 011. Combined with the exceptionally large benzene column density of SMP LMC 011, this supports a methyl-addition route from benzene toward alkyl-substituted aromatics. We propose that the high CH ₃ abundance is driven by the erosion of hydrogenated amorphous carbon (HAC) dust grains in the dense warm torus by UV photons from the central star and/or by shocks, which release CH ₃ directly into the gas phase. These results establish CH ₃ as a key reactive intermediate in the formation of complex hydrocarbons in C-rich circumstellar environments. Chemical models that incorporate methyl-addition reactions are needed for a better understanding of polycyclic aromatic hydrocarbon (PAH) formation pathways in evolved stars. The potential detection of alkyl-substituted aromatics such as toluene (C ₇ H ₈ ) and ethylbenzene (C ₈ H ₁₀ ) in C-rich evolved stars would provide direct confirmation of CH ₃ -driven aromatic growth in circumstellar environments.",
  "abstract_shown": true,
  "affiliations": [
    "Instituto de Astrofísica de Canarias",
    "Universidad de La Laguna (ULL)",
    "Consejo Superior de Investigaciones Científicas (CSIC)",
    "The University of Western Ontario",
    "Space Telescope Science Institute",
    "University of North Carolina",
    "Uppsala University",
    "University of Vienna",
    "Centre d’Etudes et de Recherche de Grasse (CERGA)",
    "INCLASS Common Laboratory",
    "University of Texas at Austin",
    "Universitat de Barcelona (UB)",
    "Boston College",
    "Cardiff University",
    "California Institute of Technology",
    "University of West Georgia",
    "The University of Manchester"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 20,
  "authors": [
    {
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        0,
        1
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      "name": "Jialu Li",
      "orcid": "0000-0003-0665-6505"
    },
    {
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        0,
        1
      ],
      "name": "D. A. García-Hernández",
      "orcid": "0000-0002-1693-2721"
    },
    {
      "affs": [
        0,
        1,
        2
      ],
      "name": "A. Manchado",
      "orcid": "0000-0002-3011-686X"
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    {
      "affs": [
        3
      ],
      "name": "Debayan Das",
      "orcid": "0009-0001-4100-9218"
    },
    {
      "affs": [
        3
      ],
      "name": "J. Cami",
      "orcid": "0000-0002-2666-9234"
    },
    {
      "affs": [
        3
      ],
      "name": "Els Peeters",
      "orcid": "0000-0002-2541-1602"
    },
    {
      "affs": [
        4,
        5
      ],
      "name": "G. C. Sloan",
      "orcid": "0000-0003-4520-1044"
    },
    {
      "affs": [
        6,
        7
      ],
      "name": "B. Aringer",
      "orcid": "0000-0001-9848-5410"
    },
    {
      "affs": [
        8,
        9
      ],
      "name": "J. Bernard-Salas",
      "orcid": "0000-0002-8452-8675"
    },
    {
      "affs": [
        3
      ],
      "name": "C. Bhatt",
      "orcid": "0009-0000-0191-6756"
    },
    {
      "affs": [
        3
      ],
      "name": "Nicholas Clark",
      "orcid": "0009-0009-4643-2734"
    },
    {
      "affs": [
        10
      ],
      "name": "Harriet L. Dinerstein",
      "orcid": "0000-0002-4017-5572"
    },
    {
      "affs": [
        11
      ],
      "name": "M. A. Gómez-Muñoz",
      "orcid": "0000-0002-3938-4211"
    },
    {
      "affs": [
        12
      ],
      "name": "Kathleen E. Kraemer",
      "orcid": "0000-0002-2626-7155"
    },
    {
      "affs": [
        13
      ],
      "name": "M. Matsuura",
      "orcid": "0000-0002-5529-5593"
    },
    {
      "affs": [
        14
      ],
      "name": "R. Sahai",
      "orcid": "0000-0002-6858-5063"
    },
    {
      "affs": [
        15
      ],
      "name": "N. C. Sterling",
      "orcid": "0000-0002-9604-1434"
    },
    {
      "affs": [
        4
      ],
      "name": "Kevin Volk",
      "orcid": "0000-0002-3824-8832"
    },
    {
      "affs": [
        4
      ],
      "name": "G. M. Wahlgren",
      "orcid": "0000-0002-6570-4776"
    },
    {
      "affs": [
        16
      ],
      "name": "A. A. Zijlstra",
      "orcid": "0000-0002-3171-5469"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/e5jzsnn8h62ag.bib",
  "cited_by": 0,
  "doi": "10.3847/2041-8213/aea794",
  "fulltext_url": null,
  "id": "e5jzsnn8h62ag",
  "issns": [
    "2041-8205",
    "2041-8213"
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  "landing_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aea794",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
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      "openalex",
      "3103|Astrophysics and Star Formation Studies"
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aea794/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-30",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/e5jzsnn8h62ag.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:13Z",
      "native_id": "10.3847/2041-8213/aea794",
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      "url": "https://iopscience.iop.org/article/10.3847/2041-8213/aea794"
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  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Astrophysics and Star Formation Studies",
      "subfield": "stellar"
    }
  ],
  "title": "The JWST Proto-PAH Project: Detection of the Methyl Radical CH ₃ in the Highly Evolved C-rich Object SMP LMC 011",
  "title_text": "The JWST Proto-PAH Project: Detection of the Methyl Radical CH ₃ in the Highly Evolved C-rich Object SMP LMC 011",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:13Z",
  "url": "https://research.draconitic.com/paper/e5jzsnn8h62ag",
  "venue": "The Astrophysical Journal Letters",
  "versions": []
}