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

Free access article

Issue		A&A Volume 416, Number 1, March II 2004


Page(s)		125 - 136
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20034238

A&A 416, 125-136 (2004)
DOI: 10.1051/0004-6361:20034238

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

N. R. Deacon

and N. C. Hambly

Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
(Received 28 August 2003 / Accepted 28 October 2003 )

Abstract
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 ( $5^{\circ}$ 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 ( $\xi(m) = m^{-\alpha}$ ) with $\alpha=0.86^{+0.14}_{-0.19}$ . 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.

Key words: astrometry -- stars: low mass, brown dwarfs -- Galaxy: open clusters and associations: individual: Alpha Per, Pleiades

Offprint request: N. R. Deacon, nd@roe.ac.uk

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