Astrometric study of the HIP 77911 CBPs candidates. Each panel shows the astrometry of the a, b, and c candidates, respectively, indicated in the top right corner. The y-axis shows the position angle with respect to the central binary in degrees, and the x-axis indicates separation in arcseconds. The position of the targets in the HiCIAO epoch is shown as a blue triangle, and the black curve emerging from it represents the position where a background point source would be found with time. The orange star points out the position of the candidate at the later SPHERE epoch if it was moving with the background. The green square is the position at which it was actually found.