WISEPA J101905.63+652954.2

Background

The binary nature of WISE 1019+6529 was revealed in 2023 through Keck adaptive optics observations, following the detection of 144 MHz highly circularly polarised radio emission with the Low Frequency Array (LOFAR). The two components have spectral types T5.5 and T7.0, with polar dipole magnetic field strengths of 660 ± 300 Gauss and 460 ± 210 Gauss, respectively. The surface magnetic field strength is constrained between 51.4 and 103 Gauss, derived from cyclotron maser emission and the upper limit of H-alpha luminosity.

The radio emission could, in principle, be powered by a binary interaction if the mass loss rate is ≥25 tonnes per second. Follow-up observations over six years (52 hours of LOFAR data) detected no additional radio pulse, but the circularly polarised emission is persistent. Besides the earlier period of about 3 hours, an additional period of 0.79 hours was found, which researchers suggest could be the rotation period of the secondary; if confirmed, it would be the shortest rotation period for any brown dwarf as of October 2025.

The components of binary stars usually have similar rotation periods, but the components of WISE 1019+6529 would have very different rotation periods. Observations with three radio telescopes (LOFAR, GMRT, VLA) detected the binary only at MHz with LOFAR, missing at higher frequencies, interpreted as a cutoff created by electron cyclotron maser emission. This cutoff allowed a measurement of the polar surface field strength at 126 Gauss.