Proper motion surveys of the young open clusters Alpha Persei and the Pleiades

N. R. Deacon, N. C. Hambly

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In this paper we present surveys of two open clusters using photometry and accurate astrometry from the SuperCOSMOS microdensitometer. These use plates taken by the Palomar Oschin Schmidt Telescope giving a wide field (5° from the cluster centre in both cases), accurate positions and a long time baseline for the proper motions. Distribution functions are fitted to proper motion vector point diagrams yielding formal membership probabilities. Luminosity and mass functions are then produced along with a catalogue of high probability members. Background star contamination limited the depth of the study of Alpha Per to R=18. Due to this the mass function found for this cluster could only be fitted with a power law (ξ(m) = m-α) with α=0.86+0.14-0.19. However with the better seperation of the Pleiades' cluster proper motion from the field population results were obtained down to R=21. As the mass function produced for this cluster extends to lower masses it is possible to see the gradient becoming increasingly shallow. This mass function is well fitted by a log normal distribution. Complete tables from Appendix B are only available in electronic form at the CDS via anonymous ftp to ( or via
Original languageEnglish
Pages (from-to)125-136
JournalAstronomy & Astrophysics
Publication statusPublished - 1 Mar 2004


  • astrometry
  • stars: low mass
  • brown dwarfs
  • Galaxy: open clusters and associations: individual: Alpha Per
  • Pleiades


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