We aim to examine the detailed disc structure that arises in a misaligned binary system as a function of the disc aspect ratio h, viscosity parameter alpha, disc outer radius R, and binary inclination angle gamma_F. We also aim to examine the conditi
ons that lead to an inclined disc being disrupted by strong differential precession. We use a grid-based hydrodynamic code to perform 3D simulations. This code has a relatively low numerical viscosity compared with the SPH schemes that have been used previously to study inclined discs. This allows the influence of viscosity on the disc evolution to be tightly controlled. We find that for thick discs (h=0.05) with low alpha, efficient warp communication in the discs allows them to precess as rigid bodies with very little warping or twisting. Such discs are observed to align with the binary orbit plane on the viscous evolution time. Thinner discs with higher viscosity, in which warp communication is less efficient, develop significant twists before achieving a state of rigid-body precession. Under the most extreme conditions we consider (h=0.01, alpha=0.005 and alpha=0.1), we find that discs can become broken or disrupted by strong differential precession. Discs that become highly twisted are observed to align with the binary orbit plane on timescales much shorter than the viscous timescale, possibly on the precession time. We find agreement with previous studies that show that thick discs with low viscosity experience mild warping and precess rigidly. We also find that as h is decreased substantially, discs may be disrupted by strong differential precession, but for disc thicknesses that are significantly less (h=0.01) than those found in previous studies (h=0.03).
The primary aim of this work is to examine the effect of parabolic stellar encounters on the evolution of a Jovian-mass giant planet forming within a protoplanetary disc. We consider the effect on both the mass accretion and the migration history as
a function of encounter distance. We use a grid-based hydrodynamics code to perform 2D simulations of a system consisting of a giant planet embedded within a gaseous disc orbiting around a star, which is perturbed by a passing star on a prograde, parabolic orbit. The disc model extends out to 50 AU, and parabolic encounters are considered with impact parameters ranging from 100 - 250 AU. In agreement with previous work, we find that the disc is significantly tidally truncated for encounters < 150 AU, and the removal of angular momentum from the disc by the passing star causes a substantial inflow of gas through the disc. The gap formed by the embedded planet becomes flooded with gas, causing the gas accretion rate onto the planet to increase abruptly. Gas flow through the gap, and into the inner disc, causes the positive inner disc torques exerted on the planet to increase, resulting in a sustained period of outward migration. For weaker interactions, corresponding to an encounter distance of > 250 AU, we find that the planet-disc system experiences minimal perturbation. Our results indicate that stellar fly-bys in young clusters may significantly modify the masses and orbital parameters of giant planets forming within protostellar discs. Planets that undergo such encounters are expected to be more massive, and to orbit with larger semimajor axes, than planets in systems which have not experienced parabolic encounters.
