Kukarkin-Parenago relationship, period gap, and cause of dwarf nova outbursts.

The Kukarkin-Parenago relation (KPR) between the amplitude of eruption and the mean cycle length of dwarf novae is extended by including the orbital period. Published observational data are compiled in tables and graphs and analyzed, and it is shown that different coefficients should be introduced into the KPR for novae with periods greater than 2.8 or less than 2.2 h. The potential implications of this dual KPR for theoretical models of the nova eruption mechanism are indicated.