ASSTG Articles
Permanent URI for this collectionhttps://hdl.handle.net/2104/5502
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Browsing ASSTG Articles by Author "Carballido, Augusto"
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Item Coagulation in the Vicinity of a Gap-Opening Jupiter-Mass Planet(Astrophysical Journal, 2016-06) Carballido, AugustoWe analyze the coagulation of dust in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magnetorotational instability. From the MHD simulation, we obtain values of the gas velocities, densities, and turbulent stresses (a) close to the gap edge, (b) in one of the two gas streams that accrete onto the planet, (c) inside the low-density gap, and (d) outside the gap. The MHD values are then input into a Monte Carlo dust-coagulation algorithm which models grain sticking and compaction. We also introduce a simple implementation for bouncing, for comparison purposes. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 μm, and another one whose initial size distribution follows the Mathis–Rumpl–Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 μm. Without bouncing, our Monte Carlo calculations show steady growth of dust aggregates in all regions, and the mass-weighted (m-w) average porosity of the initially monodisperse population reaches xtremely high final values of 98%. The final m-w porosities in all other cases without bouncing range between 30% and 82%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. When bouncing is introduced, growth is slowed down in the planetary wake and inside the gap. Future studies will need to explore the effect of different planet masses and electric charge on grains.Item The magnetic field inside a protoplanetary disk gap opened by planets of different masses(Monthly Notices of the Royal Astronomical Society, 2017) Carballido, Augusto; Matthews, Lorin; Hyde, Truell W.We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets of various masses, with the aim of calculating the strength of the vertical magnetic field threading such gaps. We introduce a gravitational potential at the centre of a shearing box to compute the tidal interaction between the planets and the disc gas, which is turbulent due to the magnetorotational instability. Two types of simulations are executed: 1) In type ‘Z’, the initial magnetic field has only a uniform, vertical component, and ten planet masses between 0.66 and 6.64 thermal masses are used; 2) In type ‘YZ’, the initial magnetic field has both toroidal and vertical components, and five planet masses covering the same mass range are used. Our results show that, for low planet masses, higher values of the vertical magnetic field occur inside the gaps than outside, in agreement with the previous work. However, for massive planets, we find that the radial profiles of the field show dips near the gap centre. The interior of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values (i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one Hill radius from each planet show a moderate decrease with planet mass. These results are relevant for the magnetic structure of circumplanetary discs and their possible outflows, and may be refined to aid future observational efforts to infer planet masses from high-resolution polarimetric observations of discs with gaps.