2018ApJ...854..101B

We present the identification of WISE J135501.90-825838.9 as a spectral binary system with a slight possibility of planetary-mass components in the 130-200 Myr AB Doradus moving group. Peculiarities in the near-infrared spectrum of this source suggest it to be a blended-light binary with L6.0 ± 1.0 and T3.0 ± 1.8 or L7.0 ± 0.6 and T7.5 ± 0.4 components. Its proper motion and radial velocity as a combined-light source yield a high membership probability for AB Doradus. While the young L6+T3 case is underluminous in a color-magnitude diagram at the AB Doradus kinematic distance, the young L7+T7.5 case could be viable. Gravity-sensitive indicators are more consistent with a field-age binary. If confirmed as a young object member of AB Doradus, we estimate masses of 11 ± 1 M_Jup and 9 ± 1 M_Jup with both component masses below the Deuterium-burning mass limit. Otherwise, we find masses of 72_–5⁺⁴ and 61_–8⁺⁶ for the field L6+T3 case and 70_–4⁺² and 42_–6⁺⁵ for the field L7+T7.5 case. Our identification of WISE J135501.90-825838.9 as a candidate young spectral binary introduces a new technique for detecting and characterizing planetary-mass companions to young brown dwarfs.