We present Keck adaptive optics imaging of the L4+L4 binary HD 130948BC along with archival HST and Gemini-North observations , which together span \approx 70 % of the binary ’ s orbital period .
From the relative orbit , we determine a total dynamical mass of 0.109 \pm 0.002 M _ { \sun } ( 114 \pm 2 M _ { Jup } ) .
The flux ratio of HD 130948BC is near unity , so both components are unambiguously substellar for any plausible mass ratio .
An independent constraint on the age of the system is available from the primary HD 130948A ( G2V , [ M/H ] = 0.0 ) .
The ensemble of available indicators suggests an age comparable to the Hyades , with the most precise age being 0.79 ^ { +0.22 } _ { -0.15 } Gyr based on gyrochronology .
Therefore , HD 130948BC is now a unique benchmark among field L and T dwarfs , with a well-determined mass , luminosity , and age .
We find that substellar theoretical models disagree with our observations .
( 1 ) Both components of HD 130948BC appear to be overluminous by a factor of \approx 2–3 \times compared to evolutionary models .
The age of the system would have to be notably younger than the gyro age to ameliorate the luminosity disagreement .
( 2 ) Effective temperatures derived from evolutionary models for HD 130948B and C are inconsistent with temperatures determined from spectral synthesis for objects of similar spectral type .
Overall , regardless of the adopted age , evolutionary and atmospheric models give inconsistent results , which indicates systematic errors in at least one class of models , possibly both .
The masses of HD 130948BC happen to be very near the theoretical mass limit for lithium burning , and thus measuring the differential lithium depletion between B and C will provide a uniquely discriminating test of theoretical models .
The potential underestimate of luminosities by evolutionary models would have wide-ranging implications ; therefore , a more refined age estimate for HD 130948A is critically needed .