Abstract
Relative proper motions, their corresponding observed errors and membership probabilities of 722 stars in the old open cluster NGC 1817 region are determined from PDS measurements of 12 plate pairs. The plates have the maximum epoch dierence of 81 years and were taken with the double astrograph at Z o-S e station of Shanghai Observatory, which has an aperture of 40 cm, a focal length of 6.9 m and a plate scale of 30 00 /mm. The av- erage proper motion accuracy is 1.6 mas/yr. These proper motions are used to determine the membership probabil- ities of stars in the region. The existence of two clusters in the region (NGC 1817, NGC 1807) is discussed. The number of stars with membership probability higher than 0.7 is 416 for NGC 1817 and 14 for NGC 1807.
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