Wind Velocity Variations in the Luminous Blue Variable-Type Erupting Star of the Wolf-Rayet Binary HD 5980

Abstract

We present the wind velocity and UV luminosity variations in the Wolf-Rayet system HD 5980 obtained over a time span during which one of the stars of the system was transformed into a luminous blue variable and underwent an eruption. We are able to separate the velocity components of the two stars in the system: a stable velocity component at -1700 km s^-1 is associated with the nonerupting star, while the variable wind with velocities ranging from -500 to -3000 km s^-1 corresponds to the eruptor. The development of a fast wind following the slow wind eruptive phase is observed. Under the assumption of radiatively driven winds, these changing velocities indicate that the radius of the photosphere gradually increased during at least 12 years prior to the 1994 eruption, decreasing rapidly thereafter. An estimate of the stellar parameters indicates that the erupting star is massive (M > 40 M_⊙) and very luminous (L > 10⁶ L_⊙), and that during the eruption its radius extended beyond the binary orbit (R_* > 100 R_⊙).