On the occurrence of dwarf nova outbursts in post novae

Abstract

We show that irradiation of the accretion disc by the white dwarf limits the occurrence of dwarf nova outbursts in post nova accretion discs. After the nova explosion, the white dwarf has to cool for up to ~100 yr - depending on the orbital period (i.e., disc size) and the temperature of the white dwarf after the nova-eruption - before the disc can begin producing dwarf nova outbursts. During this time the inner disc is maintained in a hot, ionised state. Using these calculations, we interpret the long-term photometric variability of the post nova V446 Her (Nova Her 1960) which shows today regular dwarf nova outbursts. As the white dwarf in V446 Her continues to cool over the next \~10-20 yr, we predict an increase in the amplitude of outbursts and a decrease of the outburst frequency, because the decreasing irradiation of the accretion disc should allow an increasing annular extent of the accretion disc to participate in limit cycle oscillations.