An Optical and Near Infrared Search for Brown Dwarfs in the Pleiades Cluster

We have carried out a brown dwarf search over an area of 14 × 23 arcmin 2 near the central portion of the Pleiades open cluster in five optical and near-infrared bands ( i' , Z , J , H , Ks ) with 10σ detection limits of i' ∼ 22.0, J ∼ 20.0 and Ks ∼ 18.5 mag. The surveyed area has large extinction in excess of AV= 3 in the Pleiades region. We detected four new brown dwarf candidates from the colour–colour ( J − K , i' − J ) and the colour–magnitude ( J , i ′ − K ) diagrams. We estimated their masses as 0.046 M⊙ down to 0.028 M⊙. The least massive one is estimated to have a mass smaller than Roque25 or int-pl-IZ-69, and possibly the lowest-mass object found so far in the Pleiades cluster.