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 q sp 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.