ASCA spectroscopy of the hard X-ray emission from the colliding wind interaction in gamma(2) Velorum

We discuss an ASCA observation of the eccentric WC8 + 07.5 III binary gamma (2)Velorum near apastron. The X-ray spectrum is compared with two previous observations obtained when the system was near periastron, All three spectr a display a hard-emission component that undergoes strong variability over the orbital cycle. The properties of the hard X-ray emission of gamma(2)Vel are constrained by taking into account the contribution from contaminating soft X-ray sources in the vicinity of gamma(2)Vel, We find that the observ ed variations are in qualitative agreement with the predictions of collidin g wind models. We investigate for the first time the effect of uncertaintie s in the chemical composition of the X-ray emitting plasma on our understan ding of the high-energy properties of the wind interaction region. Our resu lts indicate that these uncertainties significantly affect the derived shoc k temperature and absorption column, but play a smaller role in determining the intrinsic X-ray luminosity of the colliding wind zone. We further find that the intrinsic luminosity from the hard X-ray component in gamma(2)Vel does not follow the 1/D distance relation expected from simple models of a diabatic shocks.