2011AJ....142..169B

We present λ/Δλ ∼ 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 H₂. We also identify NH₃absorption features by comparing the spectrum to recently published line lists. The spectrum is fit with BT-Settl models, indicating T_eff∼500-600 K and log g ∼4.3-5.0. This corresponds to a mass of ∼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, respectively, reflecting a thin disk Galactic orbit and fast rotation similar to other T dwarfs, suggesting a young, possibly planetary-mass brown dwarf.