Can the quiescent accretion discs in the dwarf novae OY Car and Z Cha be in a steady state?

We attempt to fit the flat brightness temperature profiles in the accretion discs in OY Car and Z Cha with steady-state models. We find that an optically thin model of the type discussed by previous authors can produce reasonable fits. The viscosity needed to produce these fits is, however, unreasonably high in the ionized regions of the disc (α∼50), with a smooth increase when hydrogen is partially ionized. We therefore conclude that these steady-state, optically thin models cannot account for the observed brightness temperature profiles. (author)