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99 Herculis: host to a circumbinary polar-ring debris disc

Authors

  • G. M. Kennedy,

    Corresponding author
    1. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
      Email: gkennedy@ast.cam.ac.uk
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  • M. C. Wyatt,

    1. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
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  • B. Sibthorpe,

    1. UK Astronomy Technology Center, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
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  • G. Duchêne,

    1. Department of Astronomy, University of California, B-20 Hearst Field Annex, Berkeley, CA 94720-3411, USA
    2. Laboratoire d’Astrophysique de Grenoble, CNRS/Université Joseph-Fourier (UMR 5571), BP 53, F-38041 Grenoble cedex 9, France
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  • P. Kalas,

    1. Department of Astronomy, University of California, B-20 Hearst Field Annex, Berkeley, CA 94720-3411, USA
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  • B. C. Matthews,

    1. Herzberg Institute of Astrophysics, National Research Council Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
    2. Department of Physics and Astronomy, University of Victoria, Finnerty Road, Victoria, BC V8W 3P6, Canada
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  • J. S. Greaves,

    1. School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS
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  • K. Y. L. Su,

    1. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
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  • M. P. Fitzgerald

    1. Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, L-413, 7000 East Avenue, Livermore, CA 94550, USA
    2. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547, USA
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Email: gkennedy@ast.cam.ac.uk

ABSTRACT

We present resolved Herschel images of a circumbinary debris disc in the 99 Herculis system. The primary is a late F-type star. The binary orbit is well characterized and we conclude that the disc is misaligned with the binary plane. Two different models can explain the observed structure. The first model is a ring of polar orbits that move in a plane perpendicular to the binary pericentre direction. We favour this interpretation because it includes the effect of secular perturbations and the disc can survive for Gyr time-scales. The second model is a misaligned ring. Because there is an ambiguity in the orientation of the ring, which could be reflected in the sky plane, this ring either has near-polar orbits similar to the first model or has a 30° misalignment. The misaligned ring, interpreted as the result of a recent collision, is shown to be implausible from constraints on the collisional and dynamical evolution. Because disc+star systems with separations similar to 99 Herculis should form coplanar, possible formation scenarios involve either a close stellar encounter or binary exchange in the presence of circumstellar and/or circumbinary discs. Discovery and characterization of systems like 99 Herculis will help understand processes that result in planetary system misalignment around both single and multiple stars.

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