Structure of accretion disks with optically thick-optically thin transitions

We present here the solution for accretion disk structure, which describes continuously the transition between optically thick and optically thin disk regions. We show that the disk structure equations without advection, used here, give two branches of solutions which do not intersect for L < L(b) less than or similar to 0.6L(Edd) for alpha = 1.0 and M(BH) = 10(8) M(.). For larger luminosities, there are no global solutions of the equations without advection. We suggest, as one of the possibilities, that advection becomes important even before, at luminosities similar to 0.1L(Edd), when the inner disk regions become unstable as a result of radiation pressure dominance and induce the transition from optically thick to optically thin disk in the global solution.