2010ApJ...715..596F

We present new far-ultraviolet observations of the young M8 brown dwarf 2MASS J12073346-3932539, which is surrounded by an accretion disk. The data were obtained using the Hubble Space Telescope-Cosmic Origins Spectrograph. Moderate-resolution spectra (R≈ 17,000-18,000) obtained in the 1150-1750 Å and 2770-2830 Å bandpasses reveal H₂ emission excited by H I Lyα photons, several ionization states of carbon (C I-C IV), and hot gas emission lines of He II and N V (T 10⁴-10⁵ K). Emission from some species that would be found in a typical thermal plasma at this temperature (Si II, Si III, Si IV, and Mg II) is not detected. The non-detections indicate that these refractory elements are depleted into grains, and that accretion shocks dominate the production of the hot gas observed on 2MASS J12073346-3932539. We use the observed C IV luminosity to constrain the mass accretion rate in this system. We use the kinematically broadened H₂ profile to confirm that the majority of the molecular emission arises in the disk, measure the radius of the inner hole of the disk (R_hole≈ 3R_*), and constrain the physical conditions of the warm molecular phase of the disk (T(H₂) 2500-4000 K). A second, most likely unresolved H₂ component is identified. This feature is either near the stellar surface in the region of the accretion shock or in a molecular outflow, although the possibility that this Jovian-like emission arises on the dayside disk of a 6 M_Jcompanion (2M1207b) cannot be conclusively ruled out. In general, we find that this young brown dwarf disk system is a low-mass analog to classical T Tauri stars that are observed to produce H₂ emission from a warm layer in their disks, such as the well-studied TW Hya and DF Tau systems.