Multiepoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components
Journal article, 2020

Surveys have shown that up to 1/10th 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. 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 hr 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/infrared observations with Markov Chain Monte Carlo 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 ± 0.0003 M o˙, and 0.0756 ± 0.0003 M o˙, respectively, representing the most precise mass estimates of any UCDs to date. Finally, we place a 3σ upper limit of 0.9 M jup au on the mass and separation of planets orbiting either of the two components.


Qicheng Zhang

California Institute of Technology (Caltech)

G. Hallinan

California Institute of Technology (Caltech)

Walter Brisken

National Radio Astronomy Observatory Socorro

Stephen Bourke

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Observation Support

California Institute of Technology (Caltech)

Aaron Golden

Armagh Observatory and Planetarium

National University of Ireland

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 897 1

Subject Categories

Accelerator Physics and Instrumentation

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology


Onsala Space Observatory



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