Effective temperatures of the disk, ionization instability strip (grey area), and disk truncation (inside ADAF). Truncation depends on the accretion rate (compare Fig. 1), in the figure solid lines for thin disk, dashed and dotted lines for ADAF; situation for a 10⁸   M_⊙ BH: with Ṁ = 1   M_⊙/yr disk reaches inward to the last stable orbit (solid line); for 0.01   M_⊙/yr the disk is truncated far out, beyond the range shown, inside ADAF only (dotted line); in between these two rates lies the critical accretion rate for spectral transition, of interest here, 0.1   M_⊙/yr = 0.05   Ṁ_Edd with disk truncation at about 1000 R_S (R_S Schwarzschild radius) (dashed line/solid line); for 10⁹   M_⊙ and 10⁷   M_⊙ BHs: only curves for the critical accretion rate are shown.