  The wind collision region (WCR) in a colliding wind binary (CWB) is a
particularly violent place, as such, it is surprising that it is also a region
where significant quantities of interstellar dust can form. In extreme cases,
approximately 30% of the total mass loss rate of a system can be converted into
dust. These regions are poorly understood, as observation and simulation of
these systems are difficult. In our previous paper we simulated dust growth in
CWB systems using an advected scalar model and found our model to be suitable
for qualitative study. For this paper we simulated the periodic dust forming
CWB (WCd) system WR140 with our dust model, to determine how dust growth
changes over the systems periastron passage. We found that dust production
increases significantly at periastron passage, which is consistent with IR
emission of the surrounding dusty shell. We also find that the dust production
rate of the system decreases rapidly as the stars recede from each other,
though the rate of decrease is significantly lower than the rate of increase
during periastron passage. This was found to be due to strong cooling and its
associated thermal instabilities, resulting in cool, high-density pockets of
gas in the WCR where dust forms. The WCR also shows a degree of hysteresis,
resulting in a radiative post-shock flow even when the stars are separated
enough for the region to behave adiabatically.
