The Massive Binary System WR 20a: Light Curve Analysis in a Colliding Wind Model

The article presents the results of the analysis of optical light curves of the massive binary system WR 20a (WN 6ha + WN 6ha). The analysis was performed with a binary system model, extending the standard Roche model for the case when both components of the system have powerful stellar winds. The model takes into account the collision of the winds and the influence of orbital motion on the collision zone. The observational light curves in BVI filters were taken from previously published papers, in which they were analyzed using the standard Roche model. The main difference between the results of our work and the previous results is that in our model the radii of the components are about 25 \% smaller. As a consequence, the luminosity of the system in our model decreased by approximately 40 \%, and the distance to the system by 20 \%. In addition, the model was able to successfully describe the observed asymmetry of the light curve with respect to the phases of the conjunctions, which is impossible in the standard Roche model. The model light curves were also compared with the observational curves obtained by the TESS satellite and the ASAS-SN project. It was shown that, taking into account recent studies of interstellar extinction in the direction of the young open cluster Westerlund 2, the distance to WR 20a obtained in our calculations is consistent with the hypothesis that WR 20a is a member of the cluster.