We report the discovery of WISE2150-7520AB ( W2150AB ) : a widely separated ( \sim 341 AU ) very low mass L1 + T8 co-moving system .
The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99 -75:20:54.6 ( MJD=57947 ) using Wide-field Infrared Survey Explorer ( WISE ) data via the Backyard Worlds : Planet 9 citizen science project .
We present Spitzer ch 1 and ch 2 photometry ( ch 1 - ch 2 = 1.41 \pm 0.04 mag ) of the secondary and FIRE prism spectra of both components .
The sources show no peculiar spectral or photometric signatures indicating that each component is likely field age .
Using all observed data and the Gaia DR2 parallax of 41.3593 \pm 0.2799 mas for W2150A we deduce fundamental parameters of log ( L _ { bol } /L _ { \sun } ) =-3.69 \pm 0.01 , T _ { eff } =2118 \pm 62 K , and an estimated mass=72 \pm 12 M _ { Jup } for the L1 and log ( L _ { bol } /L _ { \sun } ) =-5.64 \pm 0.02 , T _ { eff } =719 \pm 61 K , and an estimated mass=34 \pm 22 M _ { Jup } for the T8 .
At a physical separation of \sim 341 AU this system has E _ { bin } = 10 ^ { 41 } erg making it the lowest binding energy system of any pair with M _ { tot } < 0.1 M _ { Sun } not associated with a young cluster .
It is equivalent in estimated mass ratio , E _ { bin } , and physical separation to the \sim 2 Myr M7.25 + M8.25 binary brown dwarf 2MASS J11011926-7732383AB ( 2M1101AB ) found in the Chameleon star forming region .
W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later .