Exploring Brown Dwarf Disks in rho-Oph
by
A. Natta, L. Testi, F. Comeron, E. Oliva, F. D'Antona, C. Baffa, G. Comoretto, S. Gennari
Abstract:
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.
Mantained by:
Leonardo Testi