The Strongest Magnetic Fields on the Coolest Brown Dwarfs
Melodie Kao, Gregg Hallinan, J. Sebastian Pineda, David Stevenson,, Adam Burgasser

TL;DR
This study used high-frequency radio observations to measure strong magnetic fields on cool brown dwarfs, revealing rapid rotation as a key factor and variability in their magnetic emission structures.
Contribution
It provides the first measurements of magnetic field strengths up to 6.2 kG on late L and T dwarfs at higher frequencies, highlighting the role of rapid rotation in magnetic field generation.
Findings
Detected localized magnetic fields of 3.2 - 6.2 kG on brown dwarfs.
Found rotation periods between 1.47 - 2.28 hours, linking rapid rotation to magnetic activity.
Observed variability in magnetic emission structures on timescales shorter than a rotation period.
Abstract
We have used NSF's Karl G. Jansky Very Large Array (VLA) to observe a sample of five known radio-emitting late L and T dwarfs ranging in age from ~0.2 - 3.4Gyr. We observed each target for seven hours, extending to higher frequencies than previously attempted and establishing proportionally higher limits on maximum surface magnetic field strengths. Detections of circularly polarized pulses at 8 - 12~GHz yield measurements of 3.2 - 4.1 kG localized magnetic fields on four of our targets, including the archetypal cloud variable and likely planetary-mass object T2.5 dwarf SIMP J01365663+0933473. We additionally detect a pulse at 15 - 16.5 GHz for the T6.5 dwarf 2MASS 10475385+2124234, corresponding to a localized 5.6 kG field strength. For the same object, we tentatively detect a 16.5 - 18 GHz pulse, corresponding to a localized 6.2 kG field strength. We measure rotation periods between…
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Taxonomy
TopicsMagnetic and Electromagnetic Effects · Geomagnetism and Paleomagnetism Studies
