On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables

I present a variation on Osaki's tidal-thermal-instability model for SU UMa behavior. I suggest that in systems with the lowest mass ratios, the angular-momentum dissipation in an eccentric disk is unable to sustain the disk on the hot side of the thermal instability. This decoupling of the tidal and thermal instabilities in systems with q < 0.07 allows a better explanation of the `echo' outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa. The idea might also apply to the soft X-ray transients.