  The study of Wolf-Rayet stars plays an important role in evolutionary
theories of massive stars. Among these objects, ~ 20% are known to be in binary
systems and can therefore be used for the mass determination of these stars.
Most of these systems are not spatially resolved and spectral lines can be used
to constrain the orbital parameters. However, part of the emission may
originate in the interaction zone between the stellar winds, modifying the line
profiles and thus challenging us to use different models to interpret them. In
this work, we analyzed the HeII4686\AA + CIV4658\AA blended lines of WR30a
(WO4+O5) assuming that part of the emission originate in the wind-wind
interaction zone. In fact, this line presents a quiescent base profile,
attributed to the WO wind, and a superposed excess, which varies with the
orbital phase along the 4.6 day period. Under these assumptions, we were able
to fit the excess spectral line profile and central velocity for all phases,
except for the longest wavelengths, where a spectral line with constant
velocity seems to be present. The fit parameters provide the eccentricity and
inclination of the binary orbit, from which it is possible to constrain the
stellar masses.
