Journal Article

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

G. M. Kennedy, M. C. Wyatt, B. Sibthorpe, G. Duchêne, P. Kalas, B. C. Matthews, J. S. Greaves, K. Y. L. Su and M. P. Fitzgerald

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 3, pages 2264-2276
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20448.x
99 Herculis: host to a circumbinary polar-ring debris disc

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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.

Keywords: circumstellar matter; stars: individual: 99 Herculis

Journal Article.  10737 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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