2002A&A...389..494G

We present 0.95-2.5µm moderate (R∼500) resolution spectra of 19 ISOCAM detected sources in the Chamaeleon I dark cloud. Thirteen of these stars are candidate very low mass members of the cloud proposed by Persi et al. (2000A&A...357..219P) on basis of the mid-IR color excess. The sample also includes a bona-fide young brown dwarf (Cha Hα 1), a transition - stellar/sub-stellar - object (Cha Hα 2), one previously known T Tauri star (Sz 33) and three ISOCAM sources with no mid-IR excess. The spectra of the mid-IR color excess sources are relatively flat and featureless in this wavelength range. Both atomic and molecular lines (when in absorption) are partially veiled suggesting the presence of continuum emission from circumstellar dust. In addition some of the sources show Paschen and Brackett lines in emission. We apply the 2µm water vapor index defined by Wilking et al. (1999AJ....117..469W) to estimate spectral types. These stars have spectral types M0-8. We use Persi et al.'s stellar luminosity determinations, in combination with D'Antona & Mazzitelli latest pre-main sequence evolutionary tracks, to estimate masses and ages. The ISOCAM detected mid-IR excess sources have sub-solar masses down to the H-burning limit and a median age of few x10⁶yr, in good agreement with the higher mass members of this cloud.