Astrometric fits to water maser spots detected in the velocity range V_LSR = 9.76–10.81 km s⁻¹. (a) Measured absolute spot positions, shown as blue squares. The dashed black line is the fitted model. Expected positions from the best-fit model are shown as black dots. (b) Measured positions and best-fit model after proper motions are removed. (c) Residuals of the astrometric fit in RA (top panel) and Dec (bottom panel).