Spectroscopy of HD 5980

Two distinct components of the NV4944{AA} line are detected in emission and their radial velocity variations are used to derive masses of 61 and 66M_{sun}_, under the assumption that binary interaction effects on this atomic transition are negligible.

We propose that this binary system is the product of quasi-chemically homogeneous evolution with little or no mass transfer. Thus, both of these binary stars may be candidates for gamma-ray burst progenitors or even pair instability supernovae. Analysis of the photospheric absorption lines belonging to the third-light object in the system confirm that it consists of an O-type star in a 96.56day eccentric orbit (e=0.82) around an unseen companion.