On the nature of the LBV/WR eclipsing binary system HD 5980

HD 5980 is a multiple star system in the Small Magellanic Cloud that underwent a luminous blue variable-like eruption in 1993-1994. The erupting star (star A) forms part of a close eclipsing binary whose companion's (star B) Wolf-Rayet nature has recently been questioned. The data analyzed in this paper cover the period 1979-2002, and support the WNE classification of star B. The orbital phase-dependent variations of ultraviolet P Cygni absorption lines imply that the wind speed of star A is 1700-2200 km s-1 and that of star B is 2600-3100 km s-1. These allow an estimate of the wind-wind collision (WWC) shock cone geometry and line profiles from the WWC region. Given the assumed mass-loss rates, only a small fraction of the observed emission line profiles may originate in the WWC region. The star A+starB binary pair is likely the result of evolution with mass transfer and/or evolution with rapid rotation, and provides a magnificent opportunity for studying the processes that occur in massive multiple systems at the stages of stellar evolution just prior to the supernova event.