The brown dwarf population in Cha I

Recently, Neuhäuser & Comerón (1998) and Comerón et al. (1999) have discovered six bona-fide and candidate brown dwarfs in the young star forming cloud Cha I in Chamaeleon with spectral types from M6 to M8, all showing Hα emission. In the meantime, we have found eight more brown dwarf candidates in Cha I, also originaly selected by Hα emission and very late spectral types. We have obtained medium-resolution spectra of the seven brightest objects. All of them have radial velocities consistent with kinematic membership to Cha I and show Li 6708Å absorption. Our Cha I brown dwarf candidates with Lithium are young or sub-stellar or both. Cha Hα 1, 3, 6, and 7 are certainly brown dwarfs: Either they are as old or older than the Pleiades, ie. should have burned all their original Lithium if they were late M-type stars, or, if they are younger than the Pleiades, ie. <= 125 Myrs, then they are sub-stellar because of the young age and the late spectral types (ge M7), according to three different sets of evolutionary tracks and isochrones (Neuhäuser & Comerón, submitted). In addition, we have placed all our objects, ie. Cha Hα 1 to 13, into the H-R diagram using BVRIJKH photometry and assuming 160 pc as distance to Cha I. Comparing the position in the H-R diagram with evolutionary tracks and isochrones, several of our objects are clearly below the sub-stellar limit with ages around 1 Myr (Comerón et al., submitted). Some objects lie close to the sub-stellar limit, to classify them as either stellar or sub-stellar, evolutionary tracks of higher reliability are needed. Furthermore, X-ray, radio and Hα emission of brown dwarfs will be discussed.