We define a sample designed to select low-mass T Tauri stars and young brown
dwarfs using DENIS data in the Chamaeleon II molecular cloud. We use a star
count method to construct an extinction map of the Chamaeleon II cloud. We
select our low-mass T Tauri star and young brown dwarf candidates by their
strong infrared colour excess in the I-J/J-K_s colour-colour dereddened
diagram. We retain only objects with colours I-J>2, and spatially distributed
in groups around the cloud cores. This provides a sample of 70 stars of which 4
are previously known T Tauri stars. We have carefully checked the reliability
of all these objects by visual inspection on the DENIS images. Thanks to the
association of the optical I-band to the infra-red J and K_s bands in DENIS, we
can apply this selection method to all star formation regions observed in the
southern hemisphere. We also identify six DENIS sources with X-ray sources
detected by ROSAT. Assuming that they are reliable low-mass candidates and
using the evolutionary models for low-mass stars, we estimate the age of these
sources between 1 Myr and < 10 Myr.Comment: 7 Pages, including 3 PostScript figures. Accepted for publication in
Astronomy & Astrophysic
