2002A&A...384..999N

We present results from a deep imaging search for companions around the young bona-fide and candidate brown dwarfs Cha Hα 1 to 12 in the Cha I dark cloud, performed with HST WFPC2 (R, I, Hα), VLT FORS1 (VRI), and NTT SofI (JHK_s). We find 16 faint companion candidates around five primaries with separations between 1.5'' and 7'' and magnitudes in R & I from 19 to 25mag, i.e. up to 8 mag fainter than the primaries. While most of these companion candidates are probably unrelated background objects, there is one promising candidate, namely 1.5'' SW off the M6-dwarf Cha Hα 5. This candidate is 3.8 to 4.7 mag fainter than the primary and its colors are consistent with an early- to mid-L spectral type. Assuming the same distance (140 pc) and absorption (A_I=0.47mag) as towards the primary, the companion candidate has log (L_bol/L_☉)=-3.0±0.3. At the age of the primary (1 to 5Myrs), the faint object would have a mass of 3 to 15 Jupiter masses according to Burrows et al. (1997ApJ...491..856B) and Chabrier & Baraffe (2000ARA&A..38..337C) models. The probability for this companion candidate to be an unrelated fore- or background object is ≤0.7%, its colors are marginally consistent with a strongly reddened background K giant. One other companion candidate has infrared colors consistent with an early T-dwarf. In addition, we present indications for Cha Hα 2 being a close (∼0.2'') binary with both components very close to the sub-stellar limit. Our detection limits are such that we should have detected all companions above ∼1M_jup with separations ≥2'' (≥320AU) and all above ∼5M_jup at ≥0.35'' (≥50AU).