WISE J104915.57 - 531906.1 is a L/T brown dwarf binary located 2 pc from the Sun .
The pair contains the closest known brown dwarfs and is the third closest known system , stellar or sub-stellar .
We report comprehensive follow-up observations of this newly uncovered system .
We have determined the spectral types of both components ( L8 \pm 1 , for the primary , agreeing with the discovery paper ; T1.5 \pm 2 for the secondary , which was lacking spectroscopic type determination in the discovery paper ) and , for the first time , their radial velocities ( V _ { rad } \sim 23.1 , 19.5 km s ^ { -1 } ) using optical spectra obtained at the Southern African Large Telescope ( SALT ) and other facilities located at the South African Astronomical Observatory ( SAAO ) .
The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses , implying that they form a gravitationally bound system .
We report resolved near-infrared JHK _ { S } photometry from the IRSF telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types .
The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations .
Simultaneous optical polarimetry observations taken at the SAAO 1.9-m give a non-detection with an upper limit of 0.07 % .
For the given spectral types and absolute magnitudes , 1 Gyr theoretical models predict masses of 0.04–0.05 M _ { \odot } for the primary , and 0.03–0.05 M _ { \odot } for the secondary .