The uniqueness of determination of the photometric mass ratio of contact binary stars with applications to selected binaries

We have used a Roche -geometry code to pre -generate light curves of contact binary stars using only mass ratio q, fill out f of the Roche lobes, and the inclination i of the orbital plane. We have parametrized TESS light curves of several binaries with a trigonometric polynomial. We used our code UNiQUE to find the best fit of the overall shape of the observed light curve and its associated parameters (q, f, i). We compared these parameters to those from a rigorous modelling of our selected objects with known mass ratio qsp inferred from spectra. The method is useful to find a close solution before the full modelling. We also got an indication of possible third light present in a system.