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arXiv · 2505.04506

Main-oval auroral emission from a T6 brown dwarf: observations, modeling, and astrometry

J. C. Guirado·J. B. Climent·J. D. Bergasa·M. A. Pérez-Torres·J. M. Marcaide·L. Peña-Moñino
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Abstract

From a series of 5 GHz VLBA radio observations taken over 1-yr span, we present the detection of compact highly-polarized radio emission from the T6 brown dwarf WISE J112254.72+255022.2 compatible with electron cyclotron maser emission. Both the total and polarized lightcurves show variability in correspondence with a rotation period of 1.95+/-0.03 hr. Comparison with models indicates that the quasi-steady radio emission of this brown dwarf is produced in circumpolar auroral rings, with remarkable similarity to the main-oval auroras in Jupiter. We have detected a large 100% polarized flare in one of the VLBA epochs (2022.82) which may imply the existence of active longitudes in the auroral rings with a non-axisymmetric beaming cone radiation pattern, similar to the dusk/dawn asymmetries seen in the Jovian radio emissions. We also present a high-precision astrometric analysis of the sky motion of WISE J112254.72+255022.2, resulting in revised values of proper motion and parallax with an improvement in precision of one order of magnitude. The common kinematics of WISE J112254.72+255022.2 with its wide companion, the M-dwarf LHS 302, is confirmed with submilliarcsecond precision, suggesting that this brown dwarf may have formed by gravitational fragmentation of the outer part of a protostellar disc around LHS 302. The astrometric analysis imposes very tight bounds to the presence of low-mass companions around WISE J112254.72+255022.2, ruling out objects more massive than Saturn. Our results strengthen the analogy between radio emitting brown dwarfs and the magnetized planets of our solar system.

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J. C. Guirado, J. B. Climent, J. D. Bergasa, M. A. Pérez-Torres, J. M. Marcaide, L. Peña-Moñino. 2025-05-07. Main-oval auroral emission from a T6 brown dwarf: observations, modeling, and astrometry. https://arxiv.org/abs/2505.04506

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