We report the discovery of a wide ( 135 \pm 25 AU ) , unusually blue L5 companion 2MASS J17114559+4028578 to the nearby M4.5 dwarf G 203-50 as a result of a targeted search for common proper motion pairs in the Sloan Digital Sky Survey and the Two Micron All Sky Survey .
Adaptive Optics imaging with Subaru indicates that neither component is a nearly equal mass binary with separation > 0.18 \arcsec , and places limits on the existence of additional faint companions .
An examination of TiO and CaH features in the primary ’ s spectrum is consistent with solar metallicity and provides no evidence that G 203-50 is metal poor .
We estimate an age for the primary of 1-5 Gyr based on activity .
Assuming coevality of the companion , its age , gravity and metallicity can be constrained from properties of the primary , making it a suitable benchmark object for the calibration of evolutionary models and for determining the atmospheric properties of peculiar blue L dwarfs .
The low total mass ( M _ { tot } = 0.21 \pm 0.03 M _ { \odot } ) , intermediate mass ratio ( q = 0.45 \pm 0.14 ) , and wide separation of this system demonstrate that the star formation process is capable of forming wide , weakly bound binary systems with low mass and BD components .
Based on the sensitivity of our search we find that no more than 2.2 \% of early-to-mid M dwarfs ( 9.0 < M _ { V } < 13.0 ) have wide substellar companions with m > 0.06 M _ { \odot } .