Polar cap shape for oblate and prolate stars with the oblateness parameter a/R = {0, 0.5, 1} in blue, green, and red, respectively. The orange-dashed line shows the reference solution for the Deutsch field as a check. The obliquity from the left column to the right column is χ = {0° ,30° ,60° ,90° }. The first row is for an oblate star with one multipole of order ℓ = 1, the second row is for a spherical dipole magnetic field at the surface, the third row is for a prolate star with one multipole of order ℓ = 1, and the fourth row is for a spherical dipole magnetic field at the surface.