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 T _eff ~500-600 K and log g ~4.3-5.0. This corresponds to a mass of ~10-30 \cal {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.

This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.