Optical depth τ_dust normalized by τ_{160 μm} as a function of wavelength λ. The left panel shows the data, and the right panel the DL07 best-fit models. Temperatures for the τ_dust calculation were obtained from MBBF fits with β = 2, and are shown binned to 2 K, with the numbers of radial points are given in parentheses. Only those MBBF fits with  ≤ 2 are considered in the calculations. The dashed lines correspond to two values of β = 1.5, 2.