is plotted with respect to the total heating in the upper panel. In the lower panel, we present the ratio of direct to indirect irradiation. The direct irradiation shuts off its effect about 20 d after outburst maximum (day zero) due to shadowing (see figure 4).]{}

The disk heating in the non-irradiated disk-instability model is given by the viscous heating, $Q^+_{\rm vis}$ \[see equation (\[qvis\])\]. In the presence of irradiation, the total heating is described by $$Q^{+}_{\rm tot}~=~Q^{+}_{\rm vis}~+~F_{\rm i}~+~F_{\rm d}.$$ The presence of irradiation affects the disk structure, and hence the contribution from $Q^{+}_{\rm vis}$, itself, is altered. The resultant contribution of the irradiation to the total disk heating is presented in figure 5 for an inner, a middle, and an outer region with the model optical maximum again being defined as day zero. In the inner region ($\lta10^8$ cm), the irradiation is negligible throughout the entire evolution. The direct component is about 10 % of the indirect component in the inner region, but the total irradiative heating does not contribute substantially compared to the viscous heating. In the middle of the disk ($\sim10^{10}$ cm), the contribution of the irradiation is small, but finite. Direct irradiation is appreciable only 