An optical and near-infrared search for brown dwarfs in the Pleiades cluster

Abstract

We have carried out a brown dwarf search over an area of 14 × 23 arcmin2 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.