ISO observations of candidate young brown dwarfs

ISOCAM measurements or upper limits for low mass members of the ρ Ophiuchi embedded cluster extend the sampling of the spectral energy distributions already obtained from the ground towards longer wavelengths, where emission by circumstellar material is significant. Good fits to the combined (ground-based + ISOCAM) photometry are obtained with theoretical models of pre-main sequence evolution, complemented with models of the spectrum of circumstellar emission, synthetic spectra of cold atmospheres, and an extinction law. The most important physical parameters of the targets, such as mass and luminosity, can be estimated with more confidence than with ground-based data alone, thanks to the much more robust reconstruction of the intrinsic spectral energy distribution made possible by the new ISOCAM data. An object-by-object discussion, based on both published and new material, shows that estimates of the source temperatures from fitting of the photometry agree closely with spectroscopy for all seven sources where both techniques have been applied. The agreement between the new fits and those based on groundbased photometry alone is also reasonably good. Three of the sources are very likely to be young brown dwarfs, five are transitional, and three appear to be low mass stars.