χ² test for the full set of spin vector orientations and the full range of thermal inertias. The retrograde solutions with β_pole < −45° are given as solid lines, the prograde ones with β_pole > +45° as dashed lines, the ones where the latitude of the rotation pole is in the range −45° < β_pole < +45° are shown in dotted lines. The thicker solid and dashed lines represent the β_pole =  ± 90° solutions, the thick dashed-dotted line the Herschel pole-on geometry.