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Title: The formation of circumbinary planets
Author: Lines, Stefan Matthew
ISNI:       0000 0004 5994 8824
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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The discovery of nearly two thousand extrasolar planets over the last two decades is indicative that planets form everywhere. Exoplanet detections have been made of a plethora of planetary types and sizes across a wide range of orbital characteristics. One of the more exotic locations that planets have been discovered in is around stellar binaries. Their proximity to such a large time-dependent potential from the orbital motion of the stars can be problematic for their formation and long-term stability. Circumbinary planets, with orbits that fully encompass the binary, have been found to orbit as close as 0.3 au to the binary barycenter and are thus subject to strong gravitational perturbations. In the formation stage, the circumbinary protoplanetary disk experiences interactions with the binary which significantly alters the dynamics and hence collisional evolution of planetesimals which struggle to grow into the planets we see. To answer the question: Could observed circumbinary planets have formed in-situ? we perform a combination of N-body, hydro dynamical and subsequently hybrid simulations to investigate the feasibility of planet growth under these conditions. Our initial N-body simulations are performed in association with an advanced collision model to identify locations in the disk where planetesimals can accrete. We perform hydro dynamical simulations of circumbinary gas disks to investigate the structure and evolution of a fluid in response to a binary, across a wide range of fluid parameters. The resulting data, a quasi-steady-state surface density profile, is integrated in a semi-analytical way to account for gas feedback on planetesimals. Our work suggests that the majority of observed closely-orbiting circumbinary planets could not form in-situ due to an overwhelming number of erosive collisions caused by high impact velocities originating from the planetesimals' dynamical interaction with the binary and gas gravity. Planetary embryos must have formed further out in the disk, where velocities are lower, and this result indicates that migration is a necessary component of planetary evolution in these systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available