Spectral indices between 6 and 13 and between 13 and 31 μm for accretion disk models (circles, squares, and diamonds) and for the K5–M2, M3–M5, and M6–M9 medians (different star symbols). The circles and squares represent models for a 0.5 and 0.2  M _☉ star, respectively (which are representative for stars with K5–M2 and M3–M5 spectral types, respectively), while the diamonds are for models of a 0.05  M _☉ brown dwarf (which is representative for objects with M6–M9 spectral types). The numbers inside the symbols denote the mass accretion rates used in the models: e.g., 8 stands for 10 ⁻⁸  M _☉ yr ⁻¹. The symbol size varies with the settling parameter , with the smallest symbols for = 1 and the largest symbols for = 0.001.