METAL DEPLETION AND WARM H{sub 2} IN THE BROWN DWARF 2M1207 ACCRETION DISK

• Published in: The Astrophysical journal 2010-05, Vol.715 (1)
• Main Authors: France, Kevin, Brown, Alexander, Beland, Stephane, Linsky, Jeffrey L., Froning, Cynthia S.
• Format: Article
• Language: English
• Subjects: ACCRETION DISKS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; BOSONS; CARBON; DWARF STARS; ELECTROMAGNETIC RADIATION; ELEMENTARY PARTICLES; ELEMENTS; EMISSION; ERUPTIVE VARIABLE STARS; FAR ULTRAVIOLET RADIATION; HYDROGEN; IONIZATION; LUMINOSITY; MASS; MASSLESS PARTICLES; METALS; NONMETALS; OPTICAL PROPERTIES; PHOTONS; PHYSICAL PROPERTIES; RADIATIONS; STARS; T TAURI STARS; TELESCOPES; ULTRAVIOLET RADIATION; VARIABLE STARS
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/715/1/596

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{approx} 17,000-18,000) obtained in the 1150-1750 A and 2770-2830 A bandpasses reveal H{sub 2} emission excited by H I Ly{alpha} photons, several ionization states of carbon (C I-C IV), and hot gas emission lines of He II and N V (T {approx} 10{sup 4}-10{sup 5} 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 H{sub 2} 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{sub hole} {approx} 3R{sub *}), and constrain the physical conditions of the warm molecular phase of the disk (T(H{sub 2}) {approx} 2500-4000 K). A second, most likely unresolved H{sub 2} 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{sub J} companion (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 H{sub 2} emission from a warm layer in their disks, such as the well-studied TW Hya and DF Tau systems.