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

R. Neuhäuser, W. Brandner, J. Alves, V. Joergens, F. Comerón

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 (JHKs). 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 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

(AI = 0.47 mag) as towards the primary, the companion

candidate has log (Lbol/Lsun) = -3.0 +/- 0.3. 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{Burrows97})

and Chabrier & Baraffe (\cite{Chabrier00}) models. The probability

for this companion candidate to be an unrelated fore- or background

object is le 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 ~ 1 Mjup with separations >=2'' (>=

320 AU) and all above ~ 5 Mjup at >= 0.35''

(>= 50 AU). Based on observations obtained with the NASA/ESA Hubble

Space Telescope in program GO 8716, ESO programs 64.I-0493, 66.C-0022,

and 66.C-0310 as well as data taken from the public VLT data archive.

Department of Astrophysics
External organisation(s)
Max-Planck-Institut für extraterrestrische Physik, European Southern Observatory (Germany)
Astronomy & Astrophysics
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Peer reviewed
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