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Published September 20, 2017 | Published + Submitted
Journal Article Open

First Detection of a Strong Magnetic Field on a Bursty Brown Dwarf: Puzzle Solved


We report the first direct detection of a strong, 5 kG magnetic field on the surface of an active brown dwarf. LSR J1835+3259 is an M8.5 dwarf exhibiting transient radio and optical emission bursts modulated by fast rotation. We have detected the surface magnetic field as circularly polarized signatures in the 819 nm sodium lines when an active emission region faced the Earth. Modeling Stokes profiles of these lines reveals the effective temperature of 2800 K and log gravity acceleration of 4.5. These parameters place LSR J1835+3259 on evolutionary tracks as a young brown dwarf with the mass of 55 ± 4M_J and age of 22 ± 4 Myr. Its magnetic field is at least 5.1 kG and covers at least 11% of the visible hemisphere. The active region topology recovered using line profile inversions comprises hot plasma loops with a vertical stratification of optical and radio emission sources. These loops rotate with the dwarf in and out of view causing periodic emission bursts. The magnetic field is detected at the base of the loops. This is the first time that we can quantitatively associate brown dwarf non-thermal bursts with a strong, 5 kG surface magnetic field and solve the puzzle of their driving mechanism. This is also the coolest known dwarf with such a strong surface magnetic field. The young age of LSR J1835+3259 implies that it may still maintain a disk, which may facilitate bursts via magnetospheric accretion, like in higher-mass T Tau-type stars. Our results pave a path toward magnetic studies of brown dwarfs and hot Jupiters.

Additional Information

© 2017 The American Astronomical Society. Received 2016 February 12; revised 2017 August 10; accepted 2017 August 11; published 2017 September 20. This work was supported by the ERC Advanced Grant HotMol (http://www.hotmol.eu) ERC-2011-AdG-291659. Based on observations made with the Keck Telescope, Mauna Kea, Hawaii. We thank the Keck staff, support astronomers and, in particular, Dr. Bob Goodrich and Dr. Hien Tran for their support. S.V.B. acknowledges the support from the NASA Astrobiology Institute and the Institute for Astronomy, University of Hawaii, for the hospitality and allocation of observing time at the Keck telescope. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. we are most fortunate to have the opportunity to conduct observations from this mountain. We thank an anonymous referee for a constructive and helpful report.

Attached Files

Published - Berdyugina_2017_ApJ_847_61.pdf

Submitted - 1709.02861.pdf


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August 22, 2023
October 17, 2023