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HR 5907: Discovery of the most rapidly rotating magnetic early B-type star by the MiMeS Collaboration

Authors

  • J. H. Grunhut,

    Corresponding author
    1. Department of Physics, Engineering Physics & Astronomy, Queens University, Kingston, Ontario K7L 3N6, Canada
    2. Department of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, Ontario K7K 7B4, Canada
      E-mail: Jason.Grunhut@rmc.ca
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  • Th. Rivinius,

    1. ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile
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  • G. A. Wade,

    1. Department of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, Ontario K7K 7B4, Canada
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  • R. H. D. Townsend,

    1. Department of Astronomy, University of Wisconsin-Madison, 2535 Sterling Hall, 475 N Charter Street, Madison, WI 53706, USA
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  • W. L. F. Marcolino,

    1. Universidade Federal do Rio de Janeiro, Observatório do Valongo Ladeira Pedro Antônio, 43, CEP 20080-090, Rio de Janeiro, Brazil
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  • D. A. Bohlender,

    1. National Research Council of Canada, Herzberg Institue of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
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  • Th. Szeifert,

    1. ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile
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  • V. Petit,

    1. Department of Geology & Astronomy, West Chester University, West Chester, PA 19383, USA
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  • J. M. Matthews,

    1. Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
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  • J. F. Rowe,

    1. NASA Ames Research Center, Moffett Field, CA 94035, USA
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  • A. F. J. Moffat,

    1. Dépt. de Physique, Université de Montréal, C.P. 6128, Succursale: Centre-Ville, Montréal, QC H3C 3J7, Canada
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  • T. Kallinger,

    1. Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
    2. Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria
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  • R. Kuschnig,

    1. Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
    2. Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria
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  • D. B. Guenther,

    1. Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Marys University, Halifax, NS, B3H 3C3, Canada
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  • S. M. Rucinski,

    1. Department of Astronomy and Astrophysics, University of Toronto, 50 St George Street, Toronto, ON M5S 3H4, Canada
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  • D. Sasselov,

    1. Harvard−Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
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  • W. W. Weiss,

    1. Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Marys University, Halifax, NS, B3H 3C3, Canada
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  • the MiMeS Collaboration


  • Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

  • Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under Prog-ID 284.D-5058.

E-mail: Jason.Grunhut@rmc.ca

ABSTRACT

We report the discovery and analysis of a very strong magnetic field in the rapidly rotating early B-type star HR 5907, based on observations obtained as part of the Magnetism in Massive Stars (MiMeS) project. We infer a rotation period of 0.508 276+0.000 015−0.000 012 d from photometric and Hα EW measurements, making this the shortest period, non-degenerate, magnetic massive star known to date. From the comparison of IUE UV and optical spectroscopy with LTE bruce/kylie models we find a solid-angle integrated, uniform black-body temperature of 17 000 ± 1000 K, a projected rotational velocity of 290 ± 10 km s−1, an equatorial radius of 3.1 ± 0.2 R, a stellar mass of 5.5 ± 0.5 M, and an inclination angle of the rotation axis to our line-of-sight of 70 ± 10°. Our measurements of the longitudinal magnetic field, which vary between −500 and −2000 G, phase coherently with the rotation period and imply a surface dipole field strength of ∼15.7 kG. On the other hand, from fits to mean Least-Squares Deconvolved Stokes V line profiles we infer a dipole field strength of ∼10.4 kG. This disagreement may result from a magnetic configuration more complex than our model, and/or from the non-uniform helium surface abundance distribution. In either case we obtain a magnetic obliquity nearly aligned with the rotation axis (inline image). Our optical spectroscopy also shows weak variability in carbon, silicon and nitrogen lines. The emission variability in hydrogen Balmer and Paschen lines indicates the presence of a dense, highly structured magnetosphere, interpreted as a centrifugally supported, magnetically confined circumstellar disc.

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