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Description
We present a study of the young (30-100Myr) open cluster IC4665 with the aim to determine the shape of the mass function well into the brown dwarf regime. We photometrically select 691 low-mass and 94 brown dwarf candidate members over an area of 3.82 square degrees centred on the cluster. K-band follow-up photometry and Two-Micron All-Sky Survey (<II/246>) data allow a first filtering of contaminant objects from our catalogues. A second filtering is performed for the brightest stars using proper motion data provided by the Tycho-2 (<I/259>) and UCAC2 (<I/289>) public catalogues. Contamination by the field population for the lowest mass objects is estimated using same latitude control fields. We fit observed surface densities of various cluster populations with King profiles and find a consistent tidal radius of 1.0 degree. The presence of possible mass segregation is discussed. In most respects investigated, IC4665 is similar to other young open clusters of similar age: (1) an estimate of the mass function in the low-mass regime and crossing the hydrogen burning limit results in a power law description with slope -0.6, (2) a fraction of BD to total members between 10-19%, (3) a cusp in the mass function is seen at about the substellar boundary, (4) the best-fit lognormal function to the full mass distribution shows an average member mass of 0.32M_{sun}_ if IC4665 has an age of 50Myr.
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