Magnetic field geometry inferred for the T8 dwarf J0623. The dashed lines on the surface are lines of constant latitude in 30° intervals, with the solid line showing the equator. Dipolar field lines with a size of 3 radii are shown in grey, and the two active field lines which emit electron cyclotron maser emission are shown in purple. The emission points at 950 and 1500 MHz are marked on each active field line. The rotation and magnetic axes are also shown as straight dashed lines. The observer’s line of sight is effectively parallel to the rotation axis. The brown dwarf has a large magnetic obliquity, reminiscent of Uranus and Neptune. The active field lines are shown here with their minimum size (see Section 5.1).