Determination of proper motions and membership of the open clusters NGC 1817 and NGC 1807 ^*

¹ Shanghai Astronomical Observatory, CAS Shanghai 200030, PR China
² Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal, 647, E-08028 Barcelona, Spain
³ CCAST(World Laboratory) P.O. Box 8730, Beijing 100080, PR China

Send offprint request to: K.P. Tian or L. Balaguer-Núñez

Received: 5 January 1998
Accepted: 23 June 1998

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 difference of 81 years and were taken with the double astrograph at Zǒ-Sè station of Shanghai Observatory, which has an aperture of 40 cm, a focal length of 6.9 m and a plate scale of 30″/mm. The average proper motion accuracy is 1.6 mas/yr. These proper motions are used to determine the membership probabilities 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.