Surveys have shown that up to one tenth of all ultracool dwarfs ( UCDs ) are appreciable radio emitters , with their emission attributed to a combination of gyrosynchrotron radiation and the electron cyclotron maser instability ( ECMI ) .
2M J0746+2000AB is a close stellar binary comprised of an L0 and L1.5 dwarf that was previously identified as a source of 5 GHz radio emission .
We used very-long-baseline interferometry ( VLBI ) to precisely track the radio emission over seven epochs in 2010–2017 , and found both components to be radio emitters—the first such system identified—with the secondary component as the dominant source of emission in all epochs .
The previously identified 2.07 h periodic bursts were confirmed to originate from the secondary component , although an isolated burst was also identified from the primary component .
We additionally fitted the VLBI absolute astrometric positions jointly with existing relative orbital astrometry derived from optical/IR observations with Markov-chain Monte Carlo ( MCMC ) methods to determine the orbital parameters of the two components .
We found the masses of the primary and secondary optical components to be 0.0795 \pm 0.0003 M _ { \odot } and 0.0756 \pm 0.0003 M _ { \odot } , respectively , representing the most precise mass estimates of any UCDs to date .
Finally , we place a 3 \sigma upper limit of 0.9 M _ { \text { jup } } au on the mass and separation of planets orbiting either of the two components .