Representative PEPSI spectra used in the study (panel a). Zeeman-Doppler images of ξ Boo A (panel b) and ξ Boo B (panel c) in orthographic projection. φ is the rotational phase. Magnetic field strength is color coded and identified in the right bars in units of Gauss. Positive polarity is depicted in red, negative polarity in blue. The length of the surface dashes is proportional to field strength.