A young very low--mass object surrounded by warm dust

We present a complete low-resolution (R~100) near-IR spectrum of the substellar object GY11, a member of the ? Ophiuchi young association. The object is remarkable because of its low estimated mass and age and because it is associated with a mid-IR source, an indication of a surrounding dusty disk. Based on the comparison of our spectrum with similar spectra of field M dwarfs and atmospheric models, we obtain revised estimates of the spectral type, effective temperature, and luminosity of the central object. These parameters are used to place the object on a H-R diagram and to compare it with the predictions of pre-main-sequence evolutionary models. Our analysis suggests that the central object has a very low mass, probably below the deuterium-burning limit and in the range of 8-12 MJ, and a young age of less than 1 Myr. The IR excess is shown to be consistent with the emission of a flared, irradiated disk similar to those found in more massive brown dwarf and T Tauri systems. This result suggests that substellar objects, even the so-called isolated planetary mass objects, found in young stellar associations are produced in a similar fashion as stars, by core contraction and gravitational collapse.