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

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 NH3 absorption features by comparing the spectrum to recently published line lists. The spectrum is fit with BT-Settl models, indicating Teff ∼500–600 K and log g ∼4.3–5.0. This corresponds to a mass of ∼10–30 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.

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