Highest S/N LSD profiles. For each panel, top plot: Stokes V in red; middle plot: null diagnosis in blue; and bottom plot: Stokes I in black. The doted horizontal lines represent the ±1σ level and the dashed horizontal lines the 0 position. The vertical line marks the radial velocity of the star in the heliocentric rest frame. The profile of μ Cep is free from linear polarisation to circular polarisation cross-talk (see Sects. 3.3 and 3.4.2)