Sizes of protoplanetary discs after star-disc encounters
  Most stars do not form in isolation, but as part of a star cluster or
association. These young stars are initially surrounded by protoplanetary
discs. In these cluster environments tidal interactions with other cluster
members can alter the disc properties. Besides the disc frequency, its mass,
angular momentum, and energy, in particular the disc's size is prone to being
changed by a passing star. So far the change in disc size was only investigated
for a small number of very specific encounters. Several studies investigated
the effect of the cluster environment on the sizes of planetary systems, like
our own solar system, based on a generalisation of information from this
limited sample. We performed numerical simulations covering the wide parameter
space typical for young star clusters, to test the validity of this approach.
Here the sizes of discs after encounters are presented, based on a size
definition which is comparable to that one used in observational studies. We
find that, except for encounters between equal-mass stars, the usually applied
estimates are insufficient. They tend to severely overestimate the remaining
disc size. We show that the disc size after an encounter can be described by a
relatively simple dependence on the periastron distance and the mass ratio of
the encounter partners. This knowledge allows, for example, to pin down the
types of encounter possibly responsible for the structure of today's solar
system.
