Proper motions of stars in the region of the Orion Nebula cluster (C 0532–054)

¹ Shanghai Observatory, Chinese Academy of Science, Shanghai 200030, China
² CCAST(World Laboratory) P.O.Box 8730,Beijing 100080, China
³ Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ, UK

Send offprint request to: K.P. Tian

Received: 26 May 1994
Accepted: 20 May 1995

Abstract

Relative proper motions and membership probabilities for 333 stars within an area of by 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 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.