New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data

We present rst results from a deep (J = 18.7), wide-eld (6.5 square degrees) infrared (ZY JHK) survey in the Upper Sco association conducted within the science verication phase of the UKIRT Infrared Deep Sky Survey Galactic Cluster Survey (GCS). Cluster members dene a sequence well separated from eld stars in the (Z J,Z) colour-magnitude diagram. We have selected a total of 164 candidates with J = 10.5{ 18.7 mag from the (Z J,Z) and (Y J,Y ) diagrams. We further investigated the location of those candidates in the other colour{magnitude and colour{colour diagrams to weed out contaminants. The cross{correlation of the GCS catalogue with the 2MASS database conrms the membership of 116 photometric candidates down to 20 Jupiter masses as they lie within a 2 circle centred on the association mean motion. The nal list of cluster members contains 129 sources with masses between 0.3 and 0.007 M . We extracted a dozen new low-mass brown dwarfs below 20 MJup, the limit of previous surveys in the region. Finally, we have derived the mass function in Upper Sco over the 0.3{0.01 M mass range, best t by a single segment with a slope of index = 0.6 0.1, in agreement with previous determination in open clusters.