the peaks of the optical activity and the inner mass flow rate. If the indirect irradiation efficiency parameter, $C_{\rm X}$, is sufficiently large, $C_{\rm X}\sim10^{-2}$, the models will be heated to a permanently hot steady state (see van Paradijs 1996). To approximately reproduce the observed light curve of A0620–00, we adopt $N=2$, ${\alpha}_0$ = $10^3$, and $C_{\rm X}$ = $1.85{\times}10^{-4}$. For the chosen parameters, the outbursts in these models always begin in the outer disk. This determines the systematics of the overall outburst. In particular, for systems with a fast rise and exponential decline, the optical outburst is predicted to arise well before the increase of the mass flow rate in the inner disk that might be associated with harder flux.

We have computed several repeated outbursts in each model to achieve an approximate steady state. Our current models with irradiation show an outburst cycle of $\sim$ 4 yr. We did not attempt to reproduce longer recurrence times in this study, since our main current consideration concerned the effects of irradiation on the outburst, itself. In the disk-instability model, the recurrence time scale is related to $\alpha$, ${\dot M}_{\rm T}$, $R_{\rm out}$ and the masses of the binary components, $M_1$ 