Abstract. -Relative proper motions and membership probabilities for 333 stars within an area of 1.• 6 by 1.• 8 centred on the Orion Nebula M 42 are determined using plates taken over a period of 83 years with the double astrograph of Shanghai Observatory (scale of 30 /mm). The plates were measured with the ASTROSCAN automatic platemeasuring machine of Leiden Observatory. The average proper motion accuracy obtained for stars in the photographic magnitude range 7 to 14 is 0.3 mas/yr. Errors are somewhat larger towards fainter and brighter magnitude, but the majority lie well below 1 mas/yr. 64% of the stars have been measured successfully on at least 13 out of 18 plates. The number of stars with membership probabilities higher than 0.7 is 184. It is shown by a detailed discussion that the proper motions and membership probabilities of the stars determined in this paper are in good agreement with the results presented recently by other authors. Although there is a clear concentration in the proper motion diagram, both the remaining dispersion of the internal motions and the distribution of "members" as projected on the sky indicate that the stars in this region are not bound as one system, but do have a common origin. A similar conclusion can be drawn from a comparison with spectroscopic and radial velocity data.
Abstract. The kinematic state of the open clusters NGC 1750 and NGC 1758 has been studied using newly determined proper motions for 540 stars in a field of 1.• 5×1.• 5 in the Taurus dark cloud region. The proper motions are obtained from the reduction of PDS measurements of 20 plates that span a total time interval of 68 years, resulting in an average proper motion accuracy of 0.67 mas/yr. These proper motions are used to determine the membership probabilities of stars in the region by means of a new, improved method described in this paper. Of the 540 stars analyzed here, 332 are found to be probable members of NGC 1750, and 23 are probable members of NGC 1758. The core radii of NGC 1750 and NGC 1758 are determined to be 17 .2 and 2 .25 respectively.
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