Tuesday, August 6, 2013

1308.0648 (Zhaohuan Zhu et al.)

Particle Concentration At Planet Induced Gap Edges and Vortices: I. Inviscid 3-D Hydro Disks    [PDF]

Zhaohuan Zhu, James M. Stone, Roman R. Rafikov, Xuening Bai
We perform a systematic study of the dynamics of dust particles in protoplanetary disks with embedded planets using global 2-D and 3-D inviscid hydrodynamic simulations. We implement Lagrangian particles into magnetohydrodynamic code Athena with cylindrical coordinates and explore the behavior of dust grains with sizes spanning more than 6 orders of magnitude --- from the well-coupled to decoupled limits. We find two distinct outcomes depending on the mass of the embedded planet, which is varied between 8 M_earth to 9 M_{J}. In the presence of a low mass planet (8 M_earth), two narrow gaps start to open in the gas on each side of the planet where the density waves shock. Although these gaps are quite shallow, they dramatically affect particle drift speed and cause significant, axisymmetric dust depletion near the planet. On the other hand, a more massive planet (>0.1 M_{J}) carves out a deeper gap with sharp edges, which are unstable to the formation of vortices that later merge into a single vortex. The vortex is intrinsically 2-dimensional without strong vertical motion, and it orbits around the central star at an almost Keplerian speed. Particles with a wide range of sizes are trapped and settle to the midplane in the vortex. Dust surface density inside the vortex can be increased by more than 100 in a non-axisymmetric fashion. For very big particles we find strong eccentricity excitation, in particular around the planet and in the vicinity of the mean motion resonances, facilitating gap opening there. Our results imply that in weakly turbulent protoplanetary disk regions (e.g. the "dead zone") dust particles with a very wide range of sizes can be trapped at gap edges and inside vortices induced by planets with mass smaller than M_{J}, potentially accelerating planetesimal and planet formation there, and giving rise to distinctive features that can be probed by ALMA and EVLA.
View original: http://arxiv.org/abs/1308.0648

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