HST, VLT, and NTT imaging search for wide companions to bona-fide and candidate brown dwarfs in the Cha I dark cloud ^*

¹ MPI für extraterrestrische Physik, Giessenbachstraße 1, 85740 Garching, Germany
² European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany

Corresponding author: R. Neuhäuser, rne@mpe.mpg.de

Received: 6 November 2001
Accepted: 14 January 2002

Abstract

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 25 mag, 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 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 = 0.47 mag) as towards the primary, the companion candidate has  (. At the age of the primary (1 to 5 Myrs), the faint object would have a mass of 3 to 15 Jupiter masses according to Burrows et al. ([CITE]) and Chabrier & Baraffe ([CITE]) models. The probability for this companion candidate to be an unrelated fore- or background object is ≤ , 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 (~) binary with both components very close to the sub-stellar limit. Our detection limits are such that we should have detected all companions above ∼ 1 M_jup with separations (≥  AU) and all above ~ M_jup at ≥ (≥  AU).