The polarization of the CO(2–1) line at 230.538 GHz in the circumstellar envelope of IK Tau. Channels are averaged across intervals of 5 km s^-1  width and are labeled according to the velocity at the lower end of the spectral bin. The color indicates the CO emission and the contours are the linearly polarized intensity. Contours are drawn at a significance of 3 and 4σ (debiased, see text). The line segments indicate the electric vector polarization angle (EVPA). The beam size is indicated in the lower left corner of each panel.