Top: astrometric orbit of HD 6664 projected on the sky. North is up and east is left. The solid red line shows the orbital solution, which is orientated clockwise, and open circles mark the individual Hipparcos measurements. The dashed lines represents the scan angle which connects these one-dimensional position measurements. The blue filled circles are the mean of the Hipparcos measurements obtained during one orbit. Bottom: O−C residuals for the normal points of the orbital solution (filled blue circles) and of the five-parameter model without companion (open squares).