  We present results of a radial velocity (RV) survey for planets and brown
dwarf (BD) companions to very young BDs and (very) low-mass stars (VLMSs) in
ChaI. High-resolution echelle spectra of ChaHa1-8 and 12 (M6-M8), and B34,
CHXR74, Sz23 (M2.5-M5) were taken with UVES / VLT between 2000 and 2004. The
achieved precision (40 to 670 m/s) is sufficient to detect Jupiter mass planets
around the targets. This first RV survey of very young BDs probes multiplicity
which is a key parameter for formation in an as yet unexplored domain, in terms
of age, mass, and orbital separation. We find that the subsample of ten BDs and
VLMSs (M<0.12 Msun, M5-M8) has constant RVs on time scales of <40 days. For
them, estimates of upper limits for masses of hypothetical companions are 0.1
to 1.5 MJup (assuming 0.1 AU). This hints at a rather small multiplicity
fraction for very young BDs/VLMSs at <0.1 AU. Furthermore, the non-variable
objects demonstrate the lack of any significant RV noise due to stellar
activity down to the precision necessary to detect giant planets. Thus, very
young BDs and VLMSs are suitable targets for RV surveys for planets. Three
objects of the sample exhibit significant RV variations. For Sz23, they might
be attributed to surface activity, while for ChaHa8 (M6.5) and CHXR74 (M4.5),
the detected RV variations are on times scales of >150 days, which cannot be
explained by rotational modulation. An alternative explanation are giant
planets / BDs of at least a few Jupiter masses orbiting with periods of several
months or longer. Thus, the presented RV data indicate that orbital periods of
companions to very young BDs and (V)LMSs are possibly several months or longer,
and that orbital separations are > 0.2 AU. This parameter range has not been
covered for all targets yet, but will be probed by follow-up observations.
