the reflares (or secondary maxima) commonly observed in X-ray novae at 50–70 days after the main peaks. These were suggested to be due to irradiation of the outer portions of the disk (Mineshige, Wheeler 1989; Mineshige 1994).

We examine here some of the aspects of the effect of irradiation on the propagation of heating and cooling waves in time-dependent disks that are unstable to the ionization thermal instability. Preliminary versions of this work were presented by Kim et al. (1994), Wheeler et al. (1996), Kim et al. (1996), and Wheeler (1997, 1999). A precursor to this work was that of Saito (1989), who was the first to consider time-dependent, irradiated disks with some simplifications (discussed later). Because this is the first study of time-dependent irradiation in black-hole disks, we concentrate on qualitative effects in systems like A0620–00. The model assumptions, including a prescription for treating irradiation, are given in section 2. The global effects of irradiation are presented in section 3 and the effects of irradiation on the thermodynamics of the heating and cooling instability are given in section 4. A discussion and conclusions are given in section 5.

Disk-instability Model for Irradiated Accretion Disks
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Irradiation
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Two types 