Spectropolarimetry of WD 2047+372. In the upper panel, the black solid line shows the intensity profile, the shape of which is heavily affected by the transmission function of the atmosphere + telescope optics + instrument. The zero level of intensity is very close to the bottom of the panel, at −5 on the left-hand scale. The red solid line is the reduced Stokes V/I profile in % units. Photon-noise error bars are centred around −2.5 % and appear as a light blue background, to which the null profile (also offset by −2.5 % for display purpose) is superposed (blue solid line). The two bottom panels show the best-fit obtained by fitting with a straight line V/I as a function of the quantity ∝ λ²(1 /I) dI/ dλ). The green bars at the top and bottom of the upper panel show the spectral regions included in the correlation plots in the small lower panels.