Two different Serkowski relations illustrating the effect of each parameter on the curve. p_max yields the maximum polarization degree and occurs at λ = λ_max, while k_p relates to the width of the curve. The blue and red lines represent Serkowski models for the vicinities of 2007le and 2006cm, respectively, while the same colored symbols indicate the polarimetry, which yielded those models. The shaded areas indicate the 1σ confidence interval of the model predictions.