PROPER MOTIONS OF STARS IN THE REGION OF THE ORION NEBULA CLUSTER (C-0532-054)

Relative proper motions and membership probabilities for 333 stars wit hin an area of 1.degrees 6 by 1.degrees 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 plate-measuring mach ine 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 meas ured 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 probabili ties of the stars determined in this paper are in good agreement with the results presented recently by other authors. Although there is a c lear concentration in the proper motion diagram, both the remaining di spersion of the internal motions and the distribution of ''members'' a s 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.