{
  "id": "2204.02719",
  "version": "v1",
  "published": "2022-04-06T10:49:58.000Z",
  "updated": "2022-04-06T10:49:58.000Z",
  "title": "A study of the F-giant star $θ$ Scorpii A: a post-merger rapid rotator?",
  "authors": [
    "Fiona Lewis",
    "Jeremy Bailey",
    "Daniel V. Cotton",
    "Ian D. Howarth",
    "Lucyna Kedziora-Chudczer",
    "Floor van Leeuwen"
  ],
  "comment": "12 pages, 10 figures, Accepted by MNRAS",
  "categories": [
    "astro-ph.SR",
    "astro-ph.IM"
  ],
  "abstract": "We report high-precision observations of the linear polarization of the F1$\\,$III star $\\theta$ Scorpii. The polarization has a wavelength dependence of the form expected for a rapid rotator, but with an amplitude several times larger than seen in otherwise similar main-sequence stars. This confirms the expectation that lower-gravity stars should have stronger rotational-polarization signatures as a consequence of the density dependence of the ratio of scattering to absorption opacities. By modelling the polarization, together with additional observational constraints (incorporating a revised analysis of Hipparcos astrometry, which clarifies the system's binary status), we determine a set of precise stellar parameters, including a rotation rate $\\omega\\, (= \\Omega/\\Omega_{\\rm c})\\ge 0.94$, polar gravity $\\log{g_p} = 2.091 ^{+0.042}_{-0.039}$ (dex cgs), mass $3.10 ^{+0.37}_{-0.32}$ solar masses, and luminosity $\\log(L/Lsun) =3.149^{+0.041}_{-0.028}$. These values are incompatible with evolutionary models of single rotating stars, with the star rotating too rapidly for its evolutionary stage, and being undermassive for its luminosity. We conclude that $\\theta$ Sco A is most probably the product of a binary merger.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-04-06T10:49:58.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "post-merger rapid rotator",
      "f-giant star",
      "report high-precision observations",
      "similar main-sequence stars",
      "precise stellar parameters"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}