2015ApJ...808L..20G

We present a new radial velocity measurement that, together with a trigonometric parallax, proper motion and signs of low gravity from the literature, confirms that SDSS J111010.01+011613.1 is a new T5.5 bona fide member of AB Doradus. Fitting ≈ 6000 Folded-port InfraRed Echellette spectroscopy in the 1.20-1.33 µm region to BT-Settl atmosphere models yielded a radial velocity of 7.5±3.8 km/s. At such a young age (110-130 Myr), current evolution models predict a mass of ∼10-12, thus placing SDSS J1110+0116 well into the planetary-mass regime. We compare the fundamental properties of SDSS J1110+0116 with a sequence of seven recently identified M8-T5 brown dwarf bona fide or high-confidence candidate members of AB Doradus. We also note that its near-infrared J-K color is redder than field T5-T6 brown dwarfs, however its absolute J-band magnitude is similar to them. SDSS J1110+0116 is one of the few age-calibrated T dwarfs known to date, as well as one of the coolest bona fide members of a young moving group.