  Knowledge of the mass function in open clusters constitutes one way to
constrain the formation of low-mass stars and brown dwarfs as does the
knowledge of the frequency of multiple systems and the properties of disks. The
aim of the project is to determine the shape of the mass function in the
low-mass and substellar regimes in the pre-main sequence (27 Myr) cluster
IC4665, which is located at 350 pc from the Sun. We have cross-matched the
near-infrared photometric data from the Eighth Data Release of the UKIRT
Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey with previous
optical data obtained with the Canada-France-Hawaii wide-field camera to
improve the determination of the luminosity and mass functions in the low-mass
and substellar regimes. The availability of i and z photometry taken with the
CFH12K camera on the Canada France Hawaii Telescope added strong constraints to
the UKIDSS photometric selection in this cluster, which is located in a dense
region of our Galaxy. We have derived the luminosity and mass functions of the
cluster down to J=18.5 mag, corresponding to masses of ~0.025 Msun at the
distance and age of IC4665 according to theoretical models. In addition, we
have extracted new candidate members down to ~20 Jupiter masses in a previously
unstudied region of the cluster. We have derived the mass function over the
0.6-0.04 Msun mass range and found that it is best represented by a log-normal
function with a peak at 0.25-0.16 Msun, consistent with the determination in
the Pleiades.
