Publication of Astronomical Observatory of Belgrade, Vol. 105, 2024, Page 13, https://doi.org/10.69646/14sbac11a
BOOK OF ABSTRACTS: XIV Serbian-Bulgarian Astronomical Conference, 23 - 27 September, 2024, Vrnjačka Banja, Serbia. Editors: Milan S. Dimitrijević, Evgeni Semkov, Zoran Simić, Goran Damljanović, Momchil Dechev

W UMa-type contact binaries are close binary systems of low mass in which both components fill their inner Roche lobes. Low mass ratio systems of this type are especially interesting because there are indications that in their case components can merge and form fast- rotating stars such as FC Com stars and the blue-stragglers, and (luminous) red novae such as V1309 Sco. The condition for the onset of tidal (Darwin) instability and probable merger can be linked to some critical mass ratio below which we expect a contact system to be unstable. We give an overview of this condition and show how it can be used to identify potential mergers. At the end we discuss a number of known extreme mass ratio binaries from the literature.