REMARKABLE LONG-TERM CHANGES IN THE SMALL MAGELLANIC CLOUD WOLF-RAYETSYSTEM HD-5980

In this paper we report the remarkable changes which occurred in the S mall Magellanic Cloud W-R system HD5980 = AB5 between 1978 and 1991. W ithin this timescale, there has been a systematic enhancement (by fact ors of 2-10 depending on the line) in the equivalent widths of all emi ssion lines, and a change in the relative strengths of N III, N IV, an d N V lines. Currently, the W-R spectrum is more typical of a WN6 star than a WN3 or WN4, as it was originally classified. The terminal spee d of the wind has diminished by similar to 600 km s(-1), while the sys tem has brightened in the visual by 0.45 mag. The UV (1850 Angstrom) c ontinuum changed by less than 0.13 mag. The change from WN3 or WN4 to WN6 is unprecedented. The system appears to be composed of at least th ree stars: two WNs in mutual 19.266 day orbit and an O-type supergiant . We propose that the changes observed in HD 5980 are related to an in crease in wind density of one (or both?) of the W-R components, where the brighter WN6 component will dominate the W-R spectrum after the ch ange, and we speculate that this modification of the wind structure is driven by tidal interaction induced by a possible current periastron passage of the third component in the system.