Difference in the effective polarization spectrum from dust calculated by the power-law fitting for the dust optical depth. The line styles of the curves correspond to the frequency bands used for fitting. The thin dotted curve is the residual when the dust temperature is misestimated as T_d = 17 K. The gray colored regions correspond to r < 3 × 10⁻⁴, 3 × 10⁻³, and 0.01 in order of darkness.