A deep photometric survey of the η Chamaeleontis cluster down to the brown dwarf – planet boundary

We report the outcome of the deep optical/infrared photometric survey of the central region (33 × 33 arcmin2 or 0.9 pc2) of the η Chamaeleontis (η Cha) pre-main sequence star cluster. The completeness limits of the photometry are I= 19.1, J= 18.2 and H= 17.6, faint enough to reveal low-mass members down to the brown dwarf and planet boundary of ≈13 MJup. We found no such low-mass members in this region. Our result combined with a previous shallower (I= 17) but larger area survey indicates that low-mass objects (0.013 < M/M⊙ < 0.075) were either not created in the η Cha cluster or lost due to the early dynamical history of the cluster and ejected to outside the surveyed areas.