We present Keck laser guide star adaptive optics imaging of the M8+M8 binary 2MASS J2206 - 2047AB .
Together with archival HST , Gemini-North , and VLT data , our observations span 8.3 years of the binary ’ s 35 ^ { +6 } _ { -5 } year orbital period , and we determine a total dynamical mass of 0.15 ^ { +0.05 } _ { -0.03 } M _ { \sun } , with the uncertainty dominated by the parallax error .
Using the measured total mass and individual luminosities , the Tucson and Lyon evolutionary models both give an age for the system of 0.4 ^ { +9.6 } _ { -0.2 } Gyr , which is consistent with its thin disk space motion derived from the Besançon Galactic structure model .
Our mass measurement combined with the Tucson ( Lyon ) evolutionary models also yields precise effective temperatures , giving 2660 ^ { +90 } _ { -100 } K and 2640 ^ { +90 } _ { -100 } K ( 2550 ^ { +90 } _ { -100 } K and 2530 ^ { +90 } _ { -100 } K ) for components A and B , respectively .
These temperatures are in good agreement with estimates for other M8 dwarfs ( from the infrared flux method and the M8 mass benchmark LHS 2397aA ) , but atmospheric model fitting of the integrated-light spectrum gives hotter temperatures of 2800 \pm 100 K for both components .
This modest discrepancy can be explained by systematic errors in the atmospheric models or by a slight underestimate of the distance ( and thus mass and age ) of the system .
We also find the observed near-infrared colors and magnitudes do not agree with those predicted by the Lyon Dusty models , given the known mass of the system .