as tr o - ph / 9 51 00 84 17 O ct 1 99 5 Thermal Instability of Advection - Dominated Disks against Local Perturbations
نویسنده
چکیده
Thermal instability is examined for advection-dominated one-temperature accretion disks. We consider axisymmetric perturbations with short wavelength in the radial direction. The viscosity is assumed to be su ciently small for the vertical hydrostatic balance to hold in perturbed states. The type of viscosity is given either by the -viscosity or by a di usion-type stress tensor. Optically thick disks are found to be in general more unstable than optically thin ones. When the thermal di usion is present, the optically thin disks become stable, but the optically thick disks are still unstable. The instability of the advectiondominated disks is di erent from that of the geometrically thin disks without advection. In the case of no advection, the thermal mode behaves under no appreciable surface density change. In the case of advection-dominated disks, however, the thermal mode occurs with no appreciable pressure change (compared with the density change), when local perturbations are considered. The variations of angular momentum and of surface density associated with the perturbations lead to a thermal instability. The astrophysical implications of this instability are brie y discussed.
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