The stellar and substellar mass function in central region of the old open cluster Praesepe from deep LBT observations

Abstract

Studies of the mass function of open clusters of different ages allow us to study the efficiency with which brown dwarfs are evaporated from clusters to populate the field. Surveys in relatively old clusters (age 100Myr) do not suffer from problems found in young clusters, such as intra-cluster extinction and large uncertainties in brown dwarf models. In this paper, we present the results of a photometric survey to study the mass function of the old open cluster Praesepe (age of ∼590Myr and distance of ∼190pc), down to the substellar regime. We have performed optical (riz and Y-band) photometric survey of Praesepe with the Large Binocular Telescope Camera, for a spatial coverage of 0.61deg2 from ∼90MJ down to a 5σ detection limit at 40MJ.