Wolf-Rayet stars in the Magellanic Clouds. II - The peculiar eclipsing binary HD 5980 in the SMC

Abstract

Over seventy spectra from two observatories are combined to study this eclipsing W-R binary, which has components of type WN4 + O7 I:. The orbital period, P = 19.266 d + or - 0.003 d, and the high eccentricity, e = 0.49 + or - 0.10, are confirmed. The width of the strongest optical emission line, He II 4686, decreases by at least a factor of two at each eclipse. This is tentatively interpreted in terms of phase-dependent variations of a combination of emission from the W-R envelope as a whole, a hot localized region in the W-R envelope, and the O component wind. Radial velocity variations of He II 4686 probably do not reflect the true W-R orbit; assumption of a mass ratio similar to those observed for other early-WN binaries, along with the more reliable absorption-line orbit of the O component, yield minimum masses of eight solar masses for the W-R star and 27 solar masses for the O-star.