On the origin and evolutionary state of RZ Cassiopeiae, KO Aquilae, and S Equulei

Aims. We determine the present evolutionary state and the restrictions on the initial mass ratios of RZ Cas, KO Aql and S Equ. Methods. We compare mass-gaining stars with evolutionary models of single stars with the same mass and subsequently compare them with accretion tracks from simultaneous conservative binary evolution. Results. The gainers are in an early main sequence stage (Xc > 0.5), with KO Aql being almost unevolved (assuming quasi-thermal equilibrium). The initial donor/gainer mass ratios Mdi/Mgi must be larger than three to obtain the present mass and luminosity of the gainers.