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 = 0.86-0.19+0.14. However with the better separation 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.
- Galaxy: open clusters and associations: individual: Alpha Per, Pleiades
- Stars: low mass, brown dwarfs