Astrometric and photometric mass functions in open clusters from UKIDSS GCS DR9

Abstract

We present the results of a deep (J = 19:1 mag) infrared (ZYJHK) survey of three open clusters surveyed by the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 9: the Pleiades, α Per, and Praesepe. We have selected cluster member candidates combining photometry in five nearinfrared filters and proper motions derived from the multiple epochs provided by the UKIDSS GCS DR9. We provide revised membership for all previously published low-mass stars and brown dwarfs recovered by the GCS and complete the full census with new cluster member candidates. We find no evidence of K-band variability in all three clusters with mean dispersions of 0.06–0.09 mag, except for a few sources. We derive the cluster mass functions and find that their shapes are very similar and in agreement with the log-normal representation of the (system) field mass function although with some variations in the characteristic mass and dispersion values. Finally, we estimate the binary fraction of low-mass stars and brown dwarfs in Praesepe and the Pleiades, respectively, and compare them with the latest hydrodynamical simulations.