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Abstract: We study the type III migration of a Saturn mass planet in low viscositydiscs. The planet is found to experience cyclic episodes of rapid decay inorbital radius, each amounting to a few Hill radii. We find this to be due tothe scattering of large- scale vortices present in the disc. The origin androle of vortices in the context of type III migration is explored. It is shownthrough numerical simulations and semi- analytical modelling that spiral shocksinduced by a sufficiently massive planet will extend close to the planetorbital radius. The production of vortensity across shock tips results in thinhigh vortensity rings with a characteristic width of the local scale height.For planets with masses equal to and above that of Saturn, the rings areco-orbital features extending the entire azimuth. Linear stability analysisshow there exists unstable modes that are localised about local vortensityminima which coincide with gap edges. Simulations show that vortices arenon-linear a outcome. We used hydrodynamic simulations to examine vortex-planetinteractions. Their effect is present in discs with kinematic viscosity lessthan about an order of magnitude smaller than the typically adopted value of u = 10^{-5}\Omega pr p0^2, where r p0 and \Omega p are the initialorbital radius and angular velocity of the planet respectively. We find thatthe magnitude of viscosity affects the nature of type III migration but not theextent of the orbital decay. The role of vortices as a function of initial discmass is also explored and it is found that the amount of orbital decay duringone episode of vortex-planet interaction is independent of initial disc mass.We incorporate the concept of the co-orbital mass deficit in the analysis ofour results and link it to the presence of vortices at gap edges.

Autor: Min-Kai Lin, John C.B. Papaloizou

Fuente: https://arxiv.org/

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