How fast is the fastest-rotating O-type star in the Galaxy?
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}~λ4200, \ion{He}{i}~λ4471, and \ion{He}{ii}~λ4542. We obtained parent non-rotating counterpart (PNRC) parameters TeffPNRC=38 716±1041~K, log gPNRC=4.12±0.12, and vesin i=587±73~\kps. The central grid solution gives Ω/Ωc=0.93, ve/vc=0.77, i=65∘, Re/Rp=1.25, and an equatorial centrifugal-to-gravitational acceleration ratio ηe=0.50. Roche critical rotation requires ηe=1 and Re/Rp=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/Ωc, ve/vc, and ηe together. A controlled spherical fit with the same atmosphere grid is needed to isolate the bias from neglecting deformation and gravity darkening.}
Versions
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BibTeX
@misc{cure2026fast,
title = {{How fast is the fastest-rotating O-type star in the Galaxy?}},
author = {M. Curé and R. S. Levenhagen and D. Turis-Gallo and G. -W. Li and M. Hadjara and I. Araya and C. Arcos},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.05760},
eprint = {2611.05760},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.05760},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - How fast is the fastest-rotating O-type star in the Galaxy?
AU - M. Curé
AU - R. S. Levenhagen
AU - D. Turis-Gallo
AU - G. -W. Li
AU - M. Hadjara
AU - I. Araya
AU - C. Arcos
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2611.05760
UR - https://arxiv.org/abs/2611.05760
AB - {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}~λ4200, \ion{He}{i}~λ4471, and \ion{He}{ii}~λ4542. We obtained parent non-rotating counterpart (PNRC) parameters T_eff^PNRC=38 716±1041~K, log g^PNRC=4.12±0.12, and v_esin i=587±73~\kps. The central grid solution gives Ω/Ω_c=0.93, v_e/v_c=0.77, i=65^∘, R_e/R_p=1.25, and an equatorial centrifugal-to-gravitational acceleration ratio η_e=0.50. Roche critical rotation requires η_e=1 and R_e/R_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_c, v_e/v_c, and η_e together. A controlled spherical fit with the same atmosphere grid is needed to isolate the bias from neglecting deformation and gravity darkening.}
ER -