G. M. Kennedy, M. C. Wyatt, B. Sibthorpe, G. Duchene, P. Kalas, B. C. Matthews, J. S. Greaves, K. Y. L. Su, M. P. Fitzgerald
We present resolved Herschel images of a circumbinary debris disk in the 99
Herculis system. The primary is a late F-type star. The binary orbit is well
characterised and we conclude that the disk 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
pericenter direction. We favour this interpretation because it includes the
effect of secular perturbations and the disk can survive for Gyr timescales.
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 degree
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 disk+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 disks. Discovery and characterisation of systems like 99
Herculis will help understand processes that result in planetary system
misalignment around both single and multiple stars.
View original:
http://arxiv.org/abs/1201.1911
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