  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.
