Context :

Aims : We examine the dependence of the wind-wind collision and subsequent X-ray emission from the massive WR+O star binary WR 22 on the acceleration of the stellar winds , radiative cooling , and orbital motion .

Methods : Three dimensional ( 3D ) adaptive-mesh refinement ( AMR ) simulations are presented that include radiative driving , gravity , optically-thin radiative cooling , and orbital motion .
Simulations were performed with instantaneously accelerated and radiatively driven stellar winds .
Radiative transfer calculations were performed on the simulation output to generate synthetic X-ray data , which are used to conduct a detailed comparison against observations .

Results : When instantaneously accelerated stellar winds are adopted in the simulation , a stable wind-wind collision region ( WCR ) is established at all orbital phases .
In contrast , when the stellar winds are radiatively driven , and thus the acceleration regions of the winds are accounted for , the WCR is far more unstable .
As the stars approach periastron , the ram pressure of the WR ’ s wind overwhelms the O star ’ s and , following a significant disruption of the shocks by non-linear thin-shell instabilities ( NTSIs ) , the WCR collapses onto the O star .
X-ray calculations reveal that when a stable WCR exists the models over-predict the observed X-ray flux by more than two orders of magnitude .
The collapse of the WCR onto the O star substantially reduces the discrepancy in the 2 - 10 keV flux to a factor of \simeq 6 at \phi = 0.994 .
However , the observed spectrum is not well matched by the models .

Conclusions : We conclude that the agreement between the models and observations could be improved by increasing the ratio of the mass-loss rates in favour of the WR star to the extent that a normal wind ram pressure balance does not occur at any orbital phase , potentially leading to a sustained collapse of the WCR onto the O star .
Radiative braking may then play a significant rôle for the WCR dynamics and resulting X-ray emission .