A constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC 2391

Using the Wide Field Imager (WFI) at the ESO 2.2 m telescope at La Silla and the CPAPIR camera at the CTIO 1.5 m telescope at Cerro Tololo, we have performed an extensive, multiband photometric survey of the open cluster IC 2391 (D~146 pc, age~50 Myr, solar metallicity). Here we present the results from our photometric survey and from a spectroscopic follow-up of the central part of the survey