Unmodeled brightness excess in WR 20a’s B and V light curves near phases 0.1–0.3

Explain and accurately model the observed higher flux at orbital phases 0.1–0.3 compared to phases 0.6–0.8 in the B and V light curves of the eclipsing binary WR 20a, which neither the standard Roche model nor the steady-state colliding-wind model currently reproduces.

Background

While the colliding-wind model presented in the paper successfully captures the overall light-curve asymmetry due to the inclined wind–wind interaction zone, the authors highlight a specific discrepancy: an elevated brightness at phases 0.1–0.3 relative to 0.6–0.8 in B and V that their steady-state model (and the standard Roche model) does not fit.

They suggest non-stationary processes in the wind–wind collision zone may account for this effect, noting that averaged TESS and ASAS-SN data do not show the same excess. However, an explicit physical explanation and a model that reproduces this feature remain outstanding.