A study of six extreme low mass ratio contact binary systems

Multi-band (B, V and R) photometric and spectroscopic observations of six poorly studied contact binaries carried out at the Western Sydney University and Las Cumbres Observatory were analyzed using a recent version of the Wilson–Devenney code. All six were found to be of extreme low mass ratio ranging from 0.073 to 0.149. All are of F spectral class with the mass of the primary component ranging from 1.05M☉ to 1.48M☉. None show light curve features of enhanced choromospheric activity (O’Connel Effect) however five of the six do have significant ultraviolet excess indicating the presence of increased magnetic and chromospheric activity. Period analysis based on available survey data suggests two systems have a slowly increasing period suggesting mass transfer from the secondary to the primary, two have a slow declining period with likely mass transfer from primary to the secondary, while one shows a steady period, and one undergoing transition from a declining to increasing period suggesting possible mass transfer reversal. We also compare light curve solutions against theoretical markers of orbital stability and show that three of the six systems have mass ratios within the theoretical instability limit and may be regarded as potential merger candidates.