MASS-LOSS RATE AND HE H ABUNDANCE OF THE ERUPTING COMPONENT IN THE SMALL-MAGELLANIC-CLOUD SYSTEM HD-5980/

The binary Wolf-Rayet system HD 5980 in the Small Magellanic Cloud und erwent a major luminous blue variable-type eruptive event in 1994. It is the first such recorded event in which the apparent precursor trans its from WNE to WNL spectral types prior to the eruption. In this pape r we analyze the spectrum of the system obtained when the outburst was declining (1994 December), but the dominant spectrum was that of the eruptor. From non-LTE analysis we obtain (M)over dot = 10(-3) M. yr(-1 ), N[He]/N[H] = 0.43 (by number; Y = 0.63 by mass), upsilon(infinity) = 600 km s(-1) T = 35,500 K, and L-eruptor = 3 x 10(6) L.. A comparis on of the He/H abundance derived here and an estimate obtained from pu blished data of 20 yr ago leads us to conclude that the member of the binary system that underwent the eruption is the star formerly classif ied as an O7 supergiant. The considerable amount of He in this star in dicates that it is in transition to becoming an H-poor W-R. By compari ng the stellar parameters with single-star evolutionary tracks, we der ive that the progenitor was more massive than 120 M., and that its cur rent mass is close to 80 M..