COLD ACCRETION DISKS WITH CORONAE AND ADVECTION

Cold optically thick accretion disks with hot coronae and radial advection have been investigated. Within the framework of alpha-viscosity models, we assume that all the mass accretion and angular momentum transport take place in the cold disk, but that a fraction of the gravitational energy released is dissipated in the corona. Both the coronal energy dissipation and the advection heat transport have a stabilization effect on the thermal and viscous instabilities of the disk. If that more than similar to 95% of the total power is dissipated in the corona, then the locally unstable behavior of the disk is restricted to a relatively narrow spatial region and is found to lie in a small range of mass accretion rates. The global temporal variability of the disk can be very mild or may disappear, and which may be applicable to the low-frequency (similar to 0.04 Hz) quasi-periodic oscillations observed in black hole candidates Cyg X-1 and GRO J0422 + 32.