Modelling the spectra of colliding winds in the Wolf-Rayet WC7+O binaries WR 42 and WR 79

We have obtained complete phase coverage of the WC7+O binaries WR 42 = HD 9 7152 and WR 79 = HD 152270 with high signal-to-noise ratio (S/N), moderate- resolution spectra. Remarkable orbital phase-locked profile variations of t he C III lambda 5696 line are observed and interpreted as arising from coll iding wind effects. Within this scenario, we have modelled the spectra usin g a purely geometrical model that assumes a cone-shaped wind-wind interacti on region which partially wraps around the O star. Such modelling holds the exciting promise of revealing a number of interesting parameters for WR+O binaries, such as the orbital inclination, the streaming velocity of materi al in the interaction region and the ratio of wind momentum flux. Knowledge of these parameters in turn leads to the possibility of a better understan ding of WR star masses, mass-loss rates and wind region characteristics.