Proper motion L and T dwarf candidate members of the Pleiades

We present the results of a deep optical–near-infrared (optical–NIR) multi-epoch survey covering 2.5 deg² of the Pleiades open star cluster to search for new very low-mass brown dwarf members. A significant (∼5 yr) epoch difference exists between the optical (CFH12k I-, Z-band) and NIR (UKIRT WFCAM J-band) observations. We construct I, I−Z and Z, Z−J colour–magnitude diagrams to select candidate cluster members. Proper motions are computed for all candidate members and compared to the background field objects to further refine the sample. We recover all known cluster members within the area of our survey. In addition, we have discovered nine new candidate brown dwarf cluster members. The seven faintest candidates have red Z−J colours and show blue NIR colours. These are consistent with being L- and T-type Pleiads. Theoretical models predict their masses to be around 11M_Jup.