Revealing the brown dwarf population in the Pleiades open cluster

We present the discovery of new brown dwarfs in the young Pleiades open cluster with masses ranging from 0.08 down to 0.045 M., and other substellar candidates whose masses could be as low as 0.03 M.. They were discovered in a CCD-based photometric survey using the IZ broad-band filters (I-lim similar to 22.0) covering an area of 1 deg(2) in the central region of the cluster. Many brown dwarf candidates arose with I magnitudes fainter than 17.5 mag. Follow-up Ii photometry and optical spectroscopy obtained for some of them in the interval 17.8 less than or equal to I < 20 yield that 11 of the candidates do show clear evidences of confirmed membership in the Pleiades. Given their low luminosities and their locations in the color-magnitude diagrams compared to other cluster members, they are Pleiads very close to the substellar Limit and brown dwarfs. In particular, we have discovered 4 substellar objects that are cooler and less massive than any other cluster member previously known.