Thin shell morphology in the circumstellar medium of massive binaries
  We investigate the morphology of the collision front between the stellar
winds of binary components in two long-period binary systems, one consisting of
a hydrogen rich Wolf-Rayet star (WNL) and an O-star and the other of a Luminous
Blue Variable (LBV) and an O-star. Specifically, we follow the development and
evolution of instabilities that form in such a shell, if it is sufficiently
compressed, due to both the wind interaction and the orbital motion. We use
MPI-AMRVAC to time-integrate the equations of hydrodynamics, combined with
optically thin radiative cooling, on an adaptive mesh 3D grid. Using parameters
for generic binary systems, we simulate the interaction between the winds of
the two stars. The WNL+O star binary shows a typical example of an adiabatic
wind collision. The resulting shell is thick and smooth, showing no
instabilities. On the other hand, the shell created by the collision of the O
star wind with the LBV wind, combined with the orbital motion of the binary
components, is susceptible to thin shell instabilities, which create a highly
structured morphology. We identify the nature of the instabilities as both
linear and non-linear thin-shell instabilities, with distinct differences
between the leading and the trailing parts of the collision front. We also find
that for binaries containing a star with a (relatively) slow wind, the global
shape of the shell is determined more by the slow wind velocity and the orbital
motion of the binary, than the ram pressure balance between the two winds. The
interaction between massive binary winds needs further parametric exploration,
to identify the role and dynamical importance of multiple instabilities at the
collision front, as shown here for an LBV+O star system.
