International Summer Institute for Modeling in Astrophysics

We revisit the destruction of resonance between Neptune and Kuiper Belt Objects (KBOs) by random planetesimal scatterings, which has been studied by Murray-Clay and Chiang (2006) previously. In this work, we consider the encounters between Neptune's resonant KBOs and planetesimals and the Levy flight behavior of resonant KBOs corresponding to a single big kick. The analysis in this work is based on order-of-magnitude estimation.

A simple, fast algorithm which simulates collisions between inelastic particles in an optically thin disk orbiting a central mass is implemented to the N-body simulation code MERCURY. The hybrid symplectic integrator is used to simulate a moonlet in the Saturn ring scenario, and produced a propeller structure around the moonlet which opens a partial gap in the ring.

Using Whitney’s Monte Carlo radiative transfer code, we simulate the near IR scattered light images in both intensity and polarized intensity for a series of axisymmetric protoplanetary disk models. By measuring the properties of the images, we study the detectability of both the disks and the features of giant planet formation at early stage (i.e. gaps opened by the planets) in real observations, and the connection between the detected disk structure and the intrinsic properties of the system. We use real point spread functions of the Subaru telescope to convolve the images, in order to synthesize realistic images with the smallest spatial resolution and inner working angle which ground based instruments can provide at present. In the models without gaps, the effects of the disk depletion factor, mass, and flareness on the images are investigated, while for the models with a gap, we focus on the dependence of the detectability of the gap on the gap position, width, and depletion factor. Qualitatively, the more massive and more flared the disk is, the brighter the disk is. The gap is only visible when the disk is visible, and the deeper and wider the gap is, the larger the contrast level of the gap is.

Following the work on ray orbits in spatially hyperbolic systems by Mass and Lam (1995) and Rieutord and Valdettaro (1997) we seek to examine the behaviour of the shear layer emitted at the critical latitude in 3D in a spherical shell fllled with rotating fluid. We compare the (previously known) 3D and the 2D solutions for a sphere in an infinite domain to find the major difference being a logarithmic singularity on the rotation axis formed by a cone of shear converging to an apex. We then consider the "split disc" arrangement first considered by Walton to examine this singularity in more detail. We also consider the behaviour of the Moore and Saffman shear layers under the influence of a large-scale forcing; our motivation is primarily the dissipation of tidal energiesin astrophysical binary systems.

The aim of the work is to perform numerical simulations of the propagation of stellar jets with consistent nozzle conditions obtained from launching simulations. This novel approach provides a global picture of the jet from its launching to its interaction with the ambient medium. The flow parameters observed at a distance of a few AU from the protostellar jet DG Tau were used to constrain the global inflow conditions whereas the actual profiles of different quantities are obtained from steady-state launching simulations. A new simulation was run on time and length scales typical of stellar jets. We also investigated the effects of cooling in these jets. We find evidence of density knots in our adiabatic simulations whereas simulations with cooling have much fewer and weaker knots.

We carry out two-dimensional hydrodynamical simulations to investigate the effects of the turbulence caused by gravitational instability on the migration of a 10 Jupiter-mass planet. We model three discs with different amounts of turbulence and model two scenarios: the first scenario allows the planet to migrate immediately and we find that the migration rates are similar in all three discs, regardless of the amount of turbulence. The second method involves keeping the planet fixed on a circular orbit such that it opens up a gap, before allowing it to migrate. We find that although the gap properties appear to be similar in all three cases, the migration rate is faster in a disc with a lower amount of turbulence.