  This paper discusses evidence for and properties of disks associated to brown
dwarfs in the star-forming region rho-Oph. We selected nine objects fr om the
ISOCAM survey of Bontemps et al. (2001) that have detections in the two
mid-infrared bands (6.7 and 14.3 um), relatively low extinction and low
luminosity. We present low-resolution near-infrared spectra in the J, H and K
bands, and determine for each source spectral type, extinction, effective
temperature a nd luminosity by comparing the spectra to those of field dwarfs
and to the most recent model stellar atmospheres. The results indicate that
eight objects have spectral types M6-M7.5, effective temperature of 2600-2700
K, one has a later spectral type (M8.5) and lower temperature (about 2400 K).
The derived extinctions range between Av~2 and 8 mag. The location of the
objects on the HR diagram, in spite of the uncertainties of the evolutionary
tracks for young objects of substellar mass, indicates that all the objects are
very young and have masses below about 0.08 Msun. The coolest object in our
sample has mass in the range 8-12 Mjup (0.008-0.012 Msun). In all cases, the
mid-infrared excess is consistent with the predictions of mode ls of disks
irradiated by the central object, showing that circumstellar disks are commonly
associated to young brown dwarfs and plan etary-mass objects. Finally, we
discuss possible variations of the disk geometry among different objects, as
well as the possibility of using these data to discriminate between various f
ormation scenarios.
