A model of AW UMa

The contact binary AW UMa has an extreme mass ratio, with the more massive component close to the main sequence, while the low mass star at q ≈ 0.1 has a much larger radius than a main sequence star of a comparable mass. We propose that the secondary has almost exhausted hydrogen in its center and is much more advanced in its evolution, as suggested by Stȩpień. Presumably the secondary lost most of its mass during its evolution with part of it transferred to the present primary. After losing a large fraction of its angular momentum, the binary will evolve into a system of FK Com type.