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The Strongest Magnetic Fields on the Coolest Brown Dwarfs

Kao, Melodie M. and Hallinan, Gregg and Pineda, J. Sebastian and Stevenson, David and Burgasser, Adam (2018) The Strongest Magnetic Fields on the Coolest Brown Dwarfs. Astrophysical Journal Supplement Series, 237 (2). Art. No. 25. ISSN 1538-4365. https://resolver.caltech.edu/CaltechAUTHORS:20180808-151343056

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Abstract

We have used NSF's Karl G. Jansky Very Large Array to observe a sample of five known radio-emitting late-L and T dwarfs ranging in age from ~0.2 to 3.4 Gyr. 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 ~1.47–2.28 hr for 2MASS J10430758+2225236, 2MASS J12373919+6526148, and SDSS J04234858–0414035, supporting (i) an emerging consensus that rapid rotation may be important for producing strong dipole fields in convective dynamos, and/or (ii) rapid rotation is a key ingredient for driving the current systems powering auroral radio emission. We observe evidence of variable structure in the frequency-dependent time series of our targets on timescales shorter than a rotation period, suggesting a higher degree of variability in the current systems near the surfaces of brown dwarfs. Finally, we find that age, mass, and temperature together cannot account for the strong magnetic fields produced by our targets.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4365/aac2d5DOIArticle
https://arxiv.org/abs/1808.02485arXivDiscussion Paper
ORCID:
AuthorORCID
Kao, Melodie M.0000-0001-5125-1414
Hallinan, Gregg0000-0002-7083-4049
Pineda, J. Sebastian0000-0002-4489-0135
Stevenson, David0000-0001-9432-7159
Burgasser, Adam0000-0002-6523-9536
Additional Information:© 2018 The American Astronomical Society. Received 2017 August 2; revised 2018 May 2; accepted 2018 May 3; published 2018 July 31. M.M.K. thanks Jackie Villadsen for helping to troubleshoot calibrations and Rakesh Yadav for thoughtful and instructive discussions about dynamo modeling. M.M.K. additionally thanks the enthusiastically supportive staff at the National Radio Astronomy Observatory for their technical mentorship. Support for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This material is based in part upon work supported by the National Science Foundation under Grant AST-1654815 and the NASA Solar System Exploration Virtual Institute cooperative agreement 80ARC017M0006. G.H. acknowledges the support of the Alfred P. Sloan Foundation and the Research Corporation for Science Advancement. J.S.P. was supported by a grant from the National Science Foundation Graduate Research Fellowship under grant no. DGE-1144469. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Facility: VLA - Very Large Array. Software: CASA (McMullin et al. 2007), MATLAB (MATLAB Signal Processing Toolbox, R2016a).
Group:Astronomy Department
Funders:
Funding AgencyGrant Number
NSFAST-1654815
NASA80ARC017M0006
Alfred P. Sloan FoundationUNSPECIFIED
Research CorporationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1144469
Subject Keywords:brown dwarfs – planets and satellites: aurorae – planets and satellites: magnetic fields – radio continuum: stars – stars: individual (2MASS 10430758+2225236, 2MASS 12373919+6526148, SDSS 04234858-0414035, SIMP J01365662+0933473) – stars: magnetic field
Issue or Number:2
Record Number:CaltechAUTHORS:20180808-151343056
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180808-151343056
Official Citation:Melodie M. Kao et al 2018 ApJS 237 25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88672
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Aug 2018 14:56
Last Modified:20 Apr 2020 08:47

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