Stability of Iron-Opaque accretion disks

The thermal stability of accretion disks and the possibility of seeing a limit-cycle behavior strongly depends on the ability of the disk plasma to cool down. Various processes connected with radiation-matter interaction appearing in hot accretion disk plasma contribute to its opacity. For the case of geometrically thin and optically thick accretion disks, we can estimate the influence of several different components of the opacity function (kappa), given by the Roseland mean. In the case of high temperatures about ten million K, the electron Thomson scattering is dominant. At lower temperatures, atomic processes become important. This effect can have a locally stabilizing or destabilizing impact on the disk. Although the local MHD simulation postulated the stabilizing influence of the atomic processes, only the global time-dependent model can reveal the disk stability range. This is due to the global diffusive nature of these processes. Here, using the previously tested GLADIS code with a modified prescription for the viscous dissipation, we examine the stabilizing effect of the Iron opacity bump.

Disk model lightcurve fo rmodel with bump (upper panel) and for model with Thomson opacity (lower panel)

Disk model lightcurve for model with Iron opacity bump (upper panel) and for model with Thomson opacity (bottom panel)


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