From the radial velocities of the N iv \lambda 4058 and He ii \lambda 4686 emission lines , and the N v \lambda 4604-20 absorption lines , determined in digital spectra , we report the discovery that the X-ray bright emission line star Wack 2134 ( = WR 21a ) is a spectroscopic binary system with an orbital period of 31.673 \pm 0.002 days .
With this period , the N iv and He ii emission and N v absorption lines , which originate in the atmosphere of the primary component , define a rather eccentric binary orbit ( e=0.64 \pm 0.03 ) .
The radial velocity variations of the N v absorptions have a lower amplitude than those of the He ii emission .
Such a behaviour of the emission line radial velocities could be due to distortions produced by a superimposed absorption component from the companion .
High resolution echelle spectra observed during the quadrature phases of the binary show H and He ii absorptions of both components with a radial velocity difference of about 541 km s ^ { -1 } .
From this difference , we infer quite high values of the minimum masses , of about 87M _ { \odot } and 53M _ { \odot } for the primary and secondary components , respectively , if the radial velocity variations of the He ii emission represent the true orbit of the primary .
No He i absorption lines are observed in our spectra .
Thus , the secondary component in the Wack 2134 binary system appears to be an early O type star .
From the presence of H , He ii and N v absorptions , and N iv and C iv emissions , in the spectrum of the primary component , it most clearly resembles those of Of/WNLha type stars .