X-raying the winds of the evolved massive binary HDE228766

HDE228766 is an evolved massive binary hosting a rare Of-WN8ha transition object on a circular orbit about a normal O7 star. We have obtained XMM-Newton EPIC spectra of this system at three key orbital phases (two conjunctions and quadrature phase) that allow us to probe the absorbing column towards the wind interaction zone as seen through the wind of the O7 star and the Of-WN8ha star. We combine these observations with a simple model of the wind-wind collision to infer the properties of the wind interaction zone (opening angle of the shock cone) and constrain the properties of the stellar winds in this system.