{
  "abstract": "{Rapid rotation distorts massive stars, making parameters from spherical models inclination-dependent. We studied these effects in the extreme Galactic O-type runaway LAMOST J040643.69+542347.8.} {We re-determined its stellar and rotational parameters with an oblate, gravity-darkened photospheric model and tabulated Stark profiles for selected \\ion{He}{ii} lines.} {We fitted continuum-normalised spectra over 4000--4600\\,Å with \\texttt{ZPEKTR}, using TLUSTY/SYNSPEC emergent fluxes, limb darkening to weight their angular contribution over the visible Roche surface, Espinosa-Lara \\& Rieutord gravity darkening, and Schöning--Butler Stark profiles. Interstellar and wind- or circumstellar-dominated features were masked.} {The model reproduces \\ion{He}{ii}~$\\lambda4200$, \\ion{He}{i}~$\\lambda4471$, and \\ion{He}{ii}~$\\lambda4542$. We obtained parent non-rotating counterpart (PNRC) parameters $T_{\\rm eff}^{\\rm PNRC}=38\\,716\\pm1041$~K, $\\log g^{\\rm PNRC}=4.12\\pm0.12$, and $v_{\\rm e}\\sin i=587\\pm73$~\\kps. The central grid solution gives $Ω/Ω_{\\rm c}=0.93$, $v_{\\rm e}/v_{\\rm c}=0.77$, $i=65^\\circ$, $R_{\\rm e}/R_{\\rm p}=1.25$, and an equatorial centrifugal-to-gravitational acceleration ratio $η_{\\rm e}=0.50$. Roche critical rotation requires $η_{\\rm e}=1$ and $R_{\\rm e}/R_{\\rm p}=1.5$: despite the high angular rate, the central solution is not critical in equatorial force balance. The projected velocity exceeds, but is statistically consistent with, the previous spherical-fit value.} {\\object{LAMOST J040643.69+542347.8} has a markedly oblate, gravity-darkened photosphere. Its proximity to critical rotation should be assessed using $Ω/Ω_{\\rm c}$, $v_{\\rm e}/v_{\\rm c}$, and $η_{\\rm e}$ together. A controlled spherical fit with the same atmosphere grid is needed to isolate the bias from neglecting deformation and gravity darkening.}",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: A&A 2026",
  "arxiv": "2611.05760",
  "author_total": 7,
  "authors": [
    {
      "name": "M. Curé"
    },
    {
      "name": "R. S. Levenhagen"
    },
    {
      "name": "D. Turis-Gallo"
    },
    {
      "name": "G. -W. Li"
    },
    {
      "name": "M. Hadjara"
    },
    {
      "name": "I. Araya"
    },
    {
      "name": "C. Arcos"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9fkt45c6m3h4y.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.05760",
  "fulltext_url": null,
  "id": "9fkt45c6m3h4y",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.05760",
  "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.GA"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.05760",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-04",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9fkt45c6m3h4y.ris",
  "sources": [
    {
      "first_seen": "2026-11-05T15:20:56Z",
      "native_id": "2611.05760",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.05760"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "How fast is the fastest-rotating O-type star in the Galaxy?",
  "title_text": "How fast is the fastest-rotating O-type star in the Galaxy?",
  "type": "preprint",
  "updated_at": "2026-11-09T00:20:19Z",
  "url": "https://research.draconitic.com/paper/9fkt45c6m3h4y",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1051/0004-6361/202662863",
      "pid": "452c4553s5hc4",
      "relation": "published-as",
      "title": "How fast is the fastest-rotating O-type star in the Galaxy?. LAMOST J040643.69+542347.8",
      "venue": "Astronomy & Astrophysics"
    }
  ]
}