THE STRUCTURE OF THE BOUNDARY-LAYER BETWEEN AN ACCRETION DISK AND A CORONA

We have studied the influence of X-ray illumination by external source on the vertical structure of accretion disks in active galactic nucle i (AGN). We have shown that besides comptonization also atomic cooling and heating processes are important because of strong density gradien t in the vertical direction. We have demonstrated that the condition o f hydrostatic equilibrium leads to the existence of narrow two-phase m edium zones between an accretion disk and a corona. We discuss the str ucture of such a two-medium zone and the possible consequences of its existence. Our results can be adopted to accretion disks in galactic X -ray binaries.