A SUDDEN LUMINOUS BLUE VARIABLE-LIKE BEHAVIOR OF THE WOLF-RAYET BINARY-SYSTEM HD-5980 IN THE SMALL MAGELLANIC CLOUD

We report a sudden outburst-like behavior of the WR binary system HD 5 980 in the SMC, as disclosed by spectroscopic and photometric observat ions performed in 1994 October and November. Our spectra show that the WR type spectrum of HD 5980 has changed drastically, now exhibiting a luminous blue variable (LBV) type spectrum with strong emission of H I and He I with P Cyg profiles and weaker emissions of N II, Si II, Si III, and Fe III. The previously dominant He II 4686 Angstrom emission has remarkably weakened and other WR type emission lines have disappe ared. Our photometry of HD 5980 reveals a visual brightening of 2.3 ma g. The behavior shown by HD 5980, i.e., the transformation of a WNE st ar in a sort of LBV star, is unprecedented.