IRC+10216: observations of November 2006 for the position (− 10″, + 20″). Top left: CN (1, 1/2) → (0, 1/2) Stokes I spectrum. Bottom left: V spectrum (in black) and least-squares fit (in red) using the Crutcher et al. (1996) method described in the text. The dashed blue line shows our fit assuming C₃ = 0. Right: same for the CN transition (1, 3/2) → (0, 1/2), with, in addition, the Gaussian fit for each individual line overplotted in green and the line overlap area coloured in orange on the I spectrum.