Double-lined spectroscopic binary systems , containing a Wolf-Rayet and a massive O-type star , are key objects for the study of massive star evolution because these kinds of systems allow the determination of fundamental astrophysical parameters of their components .
We have performed spectroscopic observations of the star WR 68a as part of a dedicated monitoring program of WR stars to discover new binary systems .
We identified spectral lines of the two components of the system and disentangled the spectra .
We measured the radial velocities in the separated spectra and determined the orbital solution .
We discovered that WR 68a is a double-lined spectroscopic binary with an orbital period of 5.2207 days , very small or null eccentricity , and inclination ranging between 75 and 85 deg .
We classified the binary components as WN6 and O5.5-6 .
The WN star is less massive than the O-type star with minimum masses of 15 \pm 5 M _ { \odot } and 30 \pm 4 M _ { \odot } , respectively .
The equivalent width of the He ii \lambda 4686 emission line shows variations with the orbital phase , presenting a minimum when the WN star is in front of the system .
The light curve constructed from available photometric data presents minima in both conjunctions of the system .