Observations of colliding winds in O-type binaries

Stellar winds, will collide in a bow shock in close binary systems of O-type stars. The presence of this boundary will truncate the full spatial extent of the two individual winds, and thus the spectral lines formed in the wind will appear differently when viewed from different orientations. Here I discuss the orbital variations of the UV wind lines in a large sample of O-binaries that have been observed with the International Ultraviolet Explorer Satellite (IUE). High density regions in the wind (near the photospheres and bow shock) will produce optical emission lines, and I describe the H alpha emission properties of several systems. The physical characteristics of the component stars can now be better estimated through Doppler tomography, a numerical method to extract the individual primary and secondary spectra.