  The concept of an advection-dominated accretion flow (ADAF), with or without
wind loss, was used to describe the spectra of the galactic center source Sgr
A*, low-luminosity AGN and nuclei of elliptical galaxies (including M87). The
spectral fits of various authors show that the transition from the
geometrically thin disk to the hot flow occurs at quite different distances,
apparently not uniquely related to the mass flow rate in the disk. We compare
these results with the results of theoretical modeling where we determine the
truncation of the thin outer disk from the efficiency of mass evaporation. The
physics is the same as in the case of galactic black holes systems (Meyer et
al. 2000b). For the observationally indicated mass flow rates our model
predicts a truncation at 10^3 to 10^4 Schwarzschild radii. We discuss whether
far inside this truncation an innermost cool thin disk could exist and affect
the spectrum.
