Spot positions measured in the five epochs of the VLBA 2001–2002 data set in subregion R5 (see Fig. 1). Six groups of masers are detected (a, b, c, d, e, f), some of them (a, d, f) shown as a close-up. Colour code indicates the LSR radial velocity (km s⁻¹) of the spots. The R5 arc structure observed with the VLBA 1996 data (T2001a,b) is also shown in the upper panel. Vectors indicate the direction and values of the mean proper motions measured in the a, b, d, e and f maser groups (proper motions were not measured in c). See the animation in the Supporting Information showing the motions in the sky of these maser groups.