Astrometric and photometric mass functions of the old open cluster   Praesepe from the UKIDSS GCS
  Here we present the results of a wide-field (~36 sq. deg.) near-infrared (ZYJHK) survey of the Praesepe cluster using the Data Release 9 of the UKIRT Infrared Deep Sky Survey Galactic Clusters Survey. We selected cluster candidates of Praesepe based on astrometry and photometry. With our candidate list, we have obtained the luminosity function of Praesepe in the Z and J bands, and we have derived the mass function of Praesepe from 0.6 down to 0.072 Msol. Moreover, we have estimated the binarity of the Praesepe members in the 0.45-0.07 Msol mass range and as well as their variability. 
S. Boudreault (1,2), N. Lodieu (1,2), N. R. Deacon (3) and N. C.   Hambly (4) ((1) Instituto de Astrofisica de Canarias, (2)...
astro-ph.SR