Series of HST observations of Proxima. The main panel shows the path in the (α cos δ, δ) plane of Proxima. The filled black dots are the HST measurements used in the last iteration of the astrometric fit, while the open dots refer to the rejected measurements. The gray, solid line is the expected linear motion (i.e., without the annual-parallax contribution) of Proxima, whereas the colored line represents the astrometric solution of Proxima. The line color changes from blue to white to red as the epoch increases (from the bottom left to the top left of the plot). The inset in the main panel shows the residuals from the linear motion, which highlight the annual-parallax ellipse. The residuals of the astrometric fit as a function of α cos δ/δ coordinates are displayed in the side panels. The gray, dashed line is set to 0 as a reference. In each of these side panels, we report the standard deviation (σ_O−C and the absolute maximum scatter of the points (|∆_O−C|).