X-raying the colliding wind binary system HDE228766

We propose to observe the interacting wind binary system HDE228766 at threecarefully chosen orbital phases. This system hosts a rare OfWN8ha transitionobject whose wind crashes onto the surface of its O7 companion. The Xraybrightness and the geometry of the system offer ideal conditions to probe thewind of the transition star: by comparing Xray spectra taken at three phases,we will constrain its massloss rate, investigate the feedback of the Xrayemission on the ionization structure of the wind and study the impact of thewind interaction zone on the optical spectrum of the O7 companion. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]