Kim et al. (1992). The possible significance of the molecular opacity to the disk-instability model was raised by Cannizzo and Wheeler (1984), but no explicit presentation has been provided.

The basic implicit numerical code used to compute time-dependent disk-instability models is that given by Mineshige (1986; see also Mineshige, Wheeler 1989; Kim et al. 1992). The present disk-instability models have been improved compared to those presented by Mineshige and Wheeler (1989), in which an unreasonably small disk size ($3.16{\times}10^{10}$ cm) was adopted so as to avoid numerical instabilities and in which irradiation is ignored. These models represent an implicit computation of 21 radial zones separated by radial mesh points at fixed spacings of $\log {\delta}R \sim$ 0.22, from $\log R_{\rm in}$ = 6.5 to $\log R_{\rm out}$ = 11.0. This zoning is adequate to reproduce the qualitative features of the expected outburst light curves for our adopted prescription for the viscosity parameter (see below). It is clearly not sufficient to provide a fully satisfactory model of a time-dependent irradiated disk. These models represent the first study of both the radial and time-dependent nature of irradiated disks around black holes where the central star cannot provide a source of flux. They 