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

Abstract

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$\pm$4 M${}_{\mathrm{J}}$ and age of 22$\pm$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.

arXiv commentApJ, in press

References in corpus (37)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• A Non-Gray Theory of Extrasolar Giant Planets and Brown Dwarfs
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The Limiting Effects of Dust in Brown Dwarf Model Atmospheres
• Temperate Earth-sized planets transiting a nearby ultracool dwarf star
• Rotation and Activity in Mid-M to L Dwarfs
• Simulations of dynamo action in fully convective stars
• Non-steady Accretion in Protostars
• Magnetic field generation in fully convective rotating spheres
• The Formation and Early Evolution of Low-mass Stars and Brown Dwarfs
• Radio Observations of a Large Sample of Late-M, L, and T Dwarfs: The Distribution of Magentic Field Strengths
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• A Volume-limited Sample of 63 M7-M9.5 Dwarfs II. Activity, magnetism, and the fade of the rotation-dominated dynamo
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• Explaining the coexistence of large-scale and small-scale magnetic fields in fully convective stars
• The Magnetic Properties of an L Dwarf Derived from Simultaneous Radio, X-ray, and H-alpha Observations
• New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
• The FeH Wing-Ford Band in Spectra of M Stars
• Hydrogen Balmer Line Broadening in Solar and Stellar Flares
• Space Velocities of L- and T-type Dwarfs
• X-ray emission from young brown dwarfs in the Orion Nebula Cluster
• Self-consistent evolution of accreting low-mass stars and brown dwarfs
• Disc Frequencies for Brown Dwarfs in the Upper Scorpius OB Association: Implications for Brown Dwarf Formation Theories
• Periodic Optical Variability of Radio Detected Ultracool Dwarfs
• Intermediate Resolution Near-Infrared Spectroscopy of 36 late-M Dwarfs
• Sporadic Long-term Variability in Radio Activity from a Brown Dwarf
• Wideband Dynamic Radio Spectra of Two Ultra-cool dwarfs
• X-ray emission from the young brown dwarfs of the Taurus Molecular Cloud
• BANYAN. VIII. New Low-Mass Stars and Brown Dwarfs with Candidate Circumstellar Disks
• Comparative analysis of two formation scenarios of bursty radio emission from ultracool dwarfs
• First polarimetric observations and modeling of the FeH F^4 Delta-X^4 Delta system
• First spectropolarimetric measurement of a brown dwarf magnetic field in molecular bands
• First polarimetric measurements and modeling of the Paschen-Back effect in CaH transitions
• Paschen-Back effect in the CrH molecule and its application for magnetic field measurements on stars, brown dwarfs, and hot exoplanets
• Correcting systematic polarization effects in Keck LRISp spectropolarimetry to <0.05%

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