2 Observations, reductions and errors

The observational and reduction procedure is described in detail in W&C.

The total internal errors of the proper motions presented in Table 1 were obtained as explained in Sect. 4 of W&C. Precision levels between 8 and 19 mas/year were achieved for the proper motions. Although individual position errors were not determined, we estimate that these errors are in the range 0.15 $\hbox{$^{\prime\prime}$ }$ to 0.25 $\hbox{$^{\prime\prime}$ }$ (see W&C and references therein).