A deep multi-band investigation of IC 2391

Aims. We report the outcome of a deep multiwavelength study of the IC 2391 young open cluster. We attempt to uncover new low-mass and sub-stellar members of the cluster and identify new debris disk objects. Methods. We observed a 30 x 30 square arcmin area in IC 2391 using the wide-field imager at the ESO 2.2m telescope. The completeness limits of the photometry at the 3σ level are V = 24.7, R C = 23.7, and I C = 23.0, faint enough to reveal sub-stellar members down to ∼0.03 M ⊙ . Our membership criteria are based on use of our optical data in combination with JHK S magnitudes from the 2MASS catalog. We also estimate the physical parameters of the selected candidates. Debris disk candidates are identified on the basis of their infrared excess emission using near- and mid-infrared photometry from the Spitzer Space Telescope. Results. Our optical survey, which has a limiting magnitude at the 3σ level 1-2 mag fainter than previous optical surveys conducted in IC 2391, revealed 29 new low-mass member candidates of the cluster. We estimate the contamination to be at least ∼50%. We constrain the fraction of sub-stellar objects in the range 8-15% and discuss possible explanations of the deficit of brown dwarfs in this cluster. We also identify 10 candidates in the cluster showing IR excess emission consistent with the presence of debris disks.