{
  "abstract": "We analyse what physical quantities of SN ejecta can be obtained from a single epoch of nebular JWST spectroscopy. We provide an analytical framework, which together with a grid of helium star SUMO spectral synthesis models allows the determination of these quantities for any stripped-envelope SN. Using the framework, we derive critical electron densities for major emission lines, finding values in the range 105 − 106 cm−3. This means formation under close to LTE conditions for 200 – 300 days. We obtain ionisation fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the 56Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths $\\tau _{[Ni\\, {\\small II}]\\, 6.636}$ and $\\tau _{[Co\\, {\\small II}]\\, 10.52}$. Besides these constraints from iron group elements, one can also obtain the filling factor of the carbon burning (O/Ne/Mg) zone from [Ne ii] 12.81 μm, and the masses of Ar II and Cl I. We apply our methodology to a publicly available JWST spectrum of Type Ic SN 2024aecx. We find that this SN produced a chlorine mass of $M_{\\mathrm{Cl\\, I}} \\simeq M_{\\mathrm{Cl}} = 5.1^{+2.0}_{-1.6}\\times 10^{-4}$ M⊙, a factor a few larger than expected from stellar evolution modeling. Furthermore, we find that the SN experienced an unexpectedly small ’Ni-bubble’ effect, with $\\rho _{\\mathrm{FeHe}} = 2.5^{+0.7}_{-0.4} \\times 10^{-15}$ g cm−3 (or an expansion factor of 1 – 3 for the Ni-bubble, depending on the adopted model) at 167d for the silicon burning material. We also determine $M_{\\mathrm{Ar\\, II}} = 4.9^{+2.2}_{-1.5} \\times 10^{-4}$ M⊙, which from ionisation fractions in our NLTE models yields a best estimate of MAr = 1.1 ± 0.4 × 10−3 M⊙.",
  "abstract_shown": true,
  "affiliations": [
    "Stockholm University The Oskar Klein Centre, Department of Astronomy, , AlbaNova, SE-10691 Stockholm ,"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 2,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Stan Barmentloo",
      "orcid": "0000-0003-4800-2737"
    },
    {
      "affs": [
        0
      ],
      "name": "Anders Jerkstrand",
      "orcid": "0000-0001-8005-4030"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ay4z1b38kczgv.bib",
  "cited_by": 0,
  "doi": "10.1093/mnras/stag1990",
  "fulltext_url": null,
  "id": "ay4z1b38kczgv",
  "issns": [
    "0035-8711",
    "1365-2966"
  ],
  "landing_url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1990/8965454",
  "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": [
    [
      "openalex",
      "3103|Gamma-ray bursts and supernovae"
    ]
  ],
  "openalex": "W7223125545",
  "pdf_url": "https://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/stag1990/72259408/stag1990.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-21",
  "publisher": "Oxford University Press (OUP)",
  "ris": "https://research.draconitic.com/paper/ay4z1b38kczgv.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:17Z",
      "native_id": "10.1093/mnras/stag1990",
      "source": "crossref",
      "url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1990/8965454"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Gamma-ray bursts and supernovae",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
  "title_text": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:17Z",
  "url": "https://research.draconitic.com/paper/ay4z1b38kczgv",
  "venue": "Monthly Notices of the Royal Astronomical Society",
  "versions": [
    {
      "doi": "10.48550/arxiv.2610.32323",
      "pid": "78h258w4sgdxq",
      "relation": "preprint",
      "title": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
      "venue": "arXiv"
    }
  ]
}