{
  "id": "1411.7926",
  "version": "v1",
  "published": "2014-11-28T16:07:46.000Z",
  "updated": "2014-11-28T16:07:46.000Z",
  "title": "Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28 2561",
  "authors": [
    "G. A. Wade",
    "R. H. Barbá",
    "J. Grunhut",
    "F. Martins",
    "V. Petit",
    "J. O. Sundqvist",
    "R. H. D. Townsend",
    "N. R. Walborn",
    "E. Alecian",
    "E. J. Alfaro",
    "J. Ma\\' iz Apellániz",
    "J. I. Arias",
    "R. Gamen",
    "N. Morrell",
    "Y. Nazé",
    "A. ud-Doula",
    "the MiMeS Collaboration"
  ],
  "comment": "18 pages, accepted by MNRAS",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We report magnetic and spectroscopic observations and modeling of the Of?p star CPD -28 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High resolution spectropolarimetric data analyzed using Least-Squares Deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to phase 0.5 of the spectral ephemeris. Interpreting the 73.41 d period as the stellar rotational period, we have phased the equivalent widths and inferred longitudinal field measurements. The phased magnetic data exhibit a weak sinusoidal variation, with maximum of about 565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema approximately in phase with the (double-wave) Halpha equivalent width variation. Modeling of the Halpha equivalent width variation assuming a quasi-3D magnetospheric model produces a unique solution for the ambiguous couplet of inclination and magnetic obliquity angles: (i, beta) or (beta, i)=(35 deg,90 deg). Adopting either geometry, the longitudinal field variation yields a dipole polar intensity Bd=2.6\\pm 0.9~kG, consistent with that obtained from direct modelling of the Stokes V profiles. We derive a wind magnetic confinement parameter eta*\\simeq 100, leading to an Alfv\\'en radius RA\\simeq 3-5~R*, and a Kepler radius RK\\simeq 20~R*. This supports a physical scenario in which the Halpha emission and other line variability have their origin in an oblique, co-rotating 'dynamical magnetosphere' structure resulting from a magnetically channeled wind. Nevertheless, the details of the formation of spectral lines and their variability within this framework remain generally poorly understood.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-11-28T16:07:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "star cpd",
      "magnetic geometry",
      "spectral variability",
      "halpha equivalent width variation",
      "resolution spectropolarimetric data"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1093/mnras/stu2548",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2015,
      "month": "Mar",
      "volume": 447,
      "number": 3,
      "pages": 2551
    },
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2015MNRAS.447.2551W"
    }
  }
}