[14] It was formally named HD 5980 in the first Henry Draper Catalogue where it was given the spectral type of Oa indicating strong emission bands.

[15] The spectral type was later refined to Wa when the emission line "O" stars were recognised as a separate class.

The physical parameters of the three stars are uncertain because of the difficulties of resolving their spectra, the partial eclipses, apparent intrinsic variations with the orbital phase, and the strong variability of at least one component.

The calibration of spectral features to physical characters such as temperature has historically been complicated by the low metallicity of objects in the SMC.

It was apparently a hydrogen-poor WN3-type until about 1990, but then underwent an LBV-type outburst that saw its radius increase ten-fold and its temperature drop dramatically so that it appeared as a B hypergiant with prominent hydrogen spectral lines.

Narrow hydrogen absorption lines are not generally considered to originate from this component and do not show the same radial velocity variations.

Higher resolution spectra show smaller slower radial velocity variations and it is assumed that C itself also has a companion.

It peaked at magnitude 8.6 in September and was comfortably the brightest star in the SMC, but there are no spectra at this exact time.

[23] In November the spectrum was considered to be B1.5Ia+, a blue hypergiant with strong hydrogen and ionised metal lines in emission or with P Cygni profiles.

[11] Although HD 5980 is treated as an LBV, it does not follow the normal pattern which would be an effective temperature during outburst of around 8,500K and an A type spectrum.

[10] SMC WR stars have relatively early spectral types for their temperatures, again as a result of the low metallicity.

In some cases, an O companion does exists, but it is speculated that Wolf–Rayet stellar winds are sufficiently weak at SMC metallicities for some photospheric absorption to be seen in the spectrum.

Thus it is only slightly evolved from the main sequence, most likely still fusing hydrogen at the core, and may follow a fairly typical single star evolutionary track.

They are in a close orbit but fully detached, although it is possible that mass transfer has taken place in the past when one or other star was expanded.

The LBV was estimated to be larger than the orbital separation at the peak of its outburst, although that is effectively just a pseudo-photosphere formed by ejected material.

After ~3.1 million years, the stars were found to have an orbital period of 19.2d, and masses and luminosity similar to those that are derived from recent observations.

Depending on the mass of the core at the time of collapse they will leave a black hole or neutron star remnant.