Decoding of the light changes in eclipsing Wolf-Rayet binaries I. A non-classical approach to the solution of light curves

摘要

Aims. We present a technique to determine the orbital and physical parameters of eclipsing eccentric Wolf-Rayet + O-star binaries,where one eclipse is produced by the absorption of the O-star light by the stellar wind of the W-R star.Methods. Our method is based on the use of the empirical moments of the light curve that are integral transforms evaluated fromthe observed light curves. The optical depth along the line of sight and the limb darkening of the W-R star are modelled by simplemathematical functions, and we derive analytical expressions for the moments of the light curve as a function of the orbital parametersand the key parameters of the transparency and limb-darkening functions. These analytical expressions are then inverted in order toderive the values of the orbital inclination, the stellar radii, the fractional luminosities, and the parameters of the wind transparencyand limb-darkening laws.Results. The method is applied to the SMC W-R eclipsing binary HD 5980, a remarkable object that underwent an LBV-like event inAugust 1994. The analysis refers to the pre-outburst observational data. A synthetic light curve based on the elements derived for thesystem allows a quality assessment of the results obtained.