Shortest recurrence periods of novae

Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M WD with a mass accretion rate of 3.6 × 10^-7M yr^-1. A 1 yr recurrence period is realized for very massive (≳ 1.3 M ) WDs with very high accretion rates (≳ 1.5 × 10^-7M yr^-1). We revised our stability limit of hydrogen shell burning, which will be useful for binary evolution calculations toward Type Ia supernovae.