HD 100546 from SPHERE-ZIMPOL R′-band observations in P2 “field-stabilized” mode from Garufi et al. (2016). The plots show the polarization degree as computed in Sect. 2 (color bar, arbitrary units). The left and right panels correspond to single observations taken at the beginning and at the end of the night, respectively. The field rotation between the two observations was ~75°, which coincides with the rotation of the vector plotted along the diffraction-like artifact that is apparent close to the central star (cross) and inward of the outer disk (which appears more strongly polarized in the left panel).