Fit of the orbit of HD221420. Top left: Fit of the HD221420 RV measurements. Top right: Fit of the HD221420 astrometric acceleration in right ascension (left) and declination (right). The black points correspond to the HIPPARCOS and Gaia EDR3 proper motion measurements. In each plot, the black curve corresponds to the best fit. The color bar indicates the log-likelihood corresponding to the different fits plotted. Bottom: Corner plot of the fitted parameters of HD221420 B, considering a prior on I between 0 and 90°. An offset of 26.5 km/s is substracted from V0 and V1 to improve readability. V0, V1, V2, and V3 correspond to H03, H15, AAT, and PFS, respectively.