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Up: Optical positions and

2. Reductions of the optical positions and the proper motions

The reductions of the observational positions were performed as described in Xu et al. (1990). In the process, the different systematic differences (FK5-reference catalogues) were added to the positions of the reference catalogues with the aim of reducing the reference catalogues used in the FK5 system. The systematic differences (FK5-AGK3/SAOC) were taken using the method of Bien et al. (1978). The results were given in detail by Lu et al. (1996a).

The reduction procedure of the proper motions was as same as described in Lu et al. (1996b).

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