Effect of Y spots on the determination of the mean longitudinal magnetic field of the HgMn star HD 11753. The curves show ⟨ B_z ⟩ as a function of rotation phase for the Y map derived by Makaganiuk et al. (2012) (thick lines) and for a uniform element distribution (thin lines). a) Calculations for the dipolar field topology with a polar strength of 500 G, obliquity β = 90°, and two different orientations with respect to the reference rotation phase (solid and dashed lines). b) Calculations for the radial magnetic field map scaled according to the Y abundance distribution.