Irradiated accretion discs in post novae

We derive approximations for the relation (the so-called S-curves) of irradiated accretion discs from detailed vertical structure calculations. Using these approximations, we simulate the time-dependent behaviour of irradiated accretion discs in dwarf novae and post novae. Our calculations show, in agreement with Hameury et al. ([CITE]), that irradiation of the accretion disc should cause small "echo" outbursts immediately following normal outbursts -which contrasts with the observed dwarf nova light curves. In addition, we calculate light curves of post nova systems where the accretion disc is strongly irradiated by the hot white dwarf. We find that the visual brightness of post novae gradually decreases after the nova explosion as a result of the decreasing disc irradiation from the continuously cooling white dwarf. The rate of decline that we derive is in good agreement with the observations. While we cannot exclude that additional effects may contribute to the observed fading of post novae, e.g., a slow decrease of the accretion rate, our calculations show that irradiation from the cooling white dwarf plays an important rôle in the post nova evolution.