Left: maximum degree of polarization p = −𝒮₁₂/𝒮₁₁ for single scattering as a function of the scattering angle θ for astronomical silicate (astrosil). The incident light is unpolarized. The dashed vertical and horizontal lines indicate θ = 90° and p = 0, respectively. The symbols on the left indicate the orientation of the polarization vector after scattering, that is, perpendicular (p >  0) and parallel (p <  0) to the scattering plane. Right: intensity map of a face-on protoplanetary disk model with superimposed polarization vectors, calculated with the radiative transfer code POLARIS for the case of Rayleigh scattering, that is, x = 0.3 (top) and for the case of x = 1.9 (bottom) where a 90° change of the polarization vector orientation occurs. These maps include direct re-emission and scattered light. The length of the polarization vectors are scaled to the maximum polarization degree present in each figure.