FIRE SPECTROSCOPY OF THE ULTRA-COOL BROWN DWARF, UGPS J072227.51-054031.2: KINEMATICS, ROTATION AND ATMOSPHERIC PARAMETERS

We present lambda/Delta lambda similar to 6000 near-infrared spectroscopy of the nearby T9 dwarf, UGPS J072227.51-054031.2, obtained during the commissioning of the Folded-Port Infrared Echellette Spectrograph on the Baade Magellan telescope at Las Campanas Observatory. The spectrum is marked by significant absorption from H2O, CH4, and H-2. We also identify NH3 absorption features by comparing the spectrum to recently published line lists. The spectrum is fit with BT-Settl models, indicating T-eff similar to 500-600 K and log g similar to 4.3-5.0. This corresponds to a mass of similar to 10-30 M-Jup and an age of 1-5 Gyr, however, there are large discrepancies between the model and observed spectrum. The radial and rotational velocities of the brown dwarf are measured as 46.9 +/- 2.5 and 40 +/- 10 km s(-1), respectively, reflecting a thin disk Galactic orbit and fast rotation similar to other T dwarfs, suggesting a young, possibly planetary-mass brown dwarf.