On the Relative Surface Density Change of Thermally Unstable Accretion Disks

摘要

The relations among the relative changes of surface density, temperature,disk height and vertical integrated pressure in three kinds of thermallyunstable accretion disks were quantitatively investigated by assuming localperturbations. The surface density change was found to be very small in thelong perturbation wavelength case but can not be ignored in the shortwavelength case. It becomes significant in an optically thin, radiative coolingdominated disk when the perturbation wavelength is shorter than 15H (H is thescale height of disk) and in a geometrically thin, optically thick andradiation pressure dominated disk when the perturbation wavelength is shorterthan 50H. In an optically thick, advection-dominated disk, which is thermallyunstable against short wavelength perturbations, the relative surface densitychange is much larger. We proved the positive correlation between the changesof surface density and temperature in an optically thick, advection- dominateddisk which was previously claimed to be the essential point of its thermalinstability. Moreover, we found an anticorrelation between the changes of diskheight and temperature in an optically thick, advection-dominated disk. This isthe natural result of the absence of appreciable vertical integrated pressurechange.