A Panchromatic View of Brown Dwarf Aurorae

Abstract

Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multi-wavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as the consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestation of auroral phenomena in brown dwarf atmospheres, like H$\alpha$, and define their distinguishing characteristics. We conclude that large amplitude photometric variability in the near infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral H$\alpha$ emission and quiescent radio emission in ECMI pulsing brown dwarfs, suggesting a potential underlying physical connection between the quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems to both power the aurorae and seed the magnetosphere with plasma.

26 pages, 17 figures, and 2 tables; accepted to ApJ

References in corpus (49)

• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Large-scale magnetic topologies of late M dwarfs
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• Large-scale magnetic topologies of early M dwarfs
• Simulations of dynamo action in fully convective stars
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• The solar magnetic field
• The First Direct Measurements of Magnetic Fields on Very Low-Mass Stars
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present
• The large-scale axisymmetric magnetic topology of avery-low-mass fully-convective star
• 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
• Strong Brightness Variations Signal Cloudy-to-Clear Transition of Brown Dwarfs
• Solar-type dynamo behaviour in fully convective stars without a tachocline
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• HAZMAT I: The Evolution of Far-UV and Near-UV Emission from Early M Stars
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs
• Doppler Imaging of Exoplanets and Brown Dwarfs
• Formation and composition of planets around very low mass stars
• The Arecibo Detection of the Coolest Radio-flaring Brown Dwarf
• Tracers of Chromospheric Structure I: Observations of Ca II K and H alpha in M Dwarfs
• Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. II. Mixed Trends in VB10 and LSR1835+32 and the Possible Role of Rotation
• The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
• Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs
• Temperature Fluctuations as a Source of Brown Dwarf Variability
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• First limits on the occurrence rate of short-period planets orbiting brown dwarfs
• Simultaneous Multiwavelength Observations of Magnetic Activity in Ultracool Dwarfs. IV. The Active, Young Binary NLTT 33370 AB (=2MASS J13142039+1320011)
• Wideband Dynamic Radio Spectra of Two Ultra-cool dwarfs
• A Search for Photometric Variability in L and T type Brown Dwarf Atmospheres
• Variable and polarized radio emission from the T6 brown dwarf WISEP J112254.73+255021.5
• The ion-induced charge-exchange X-ray emission of the Jovian Auroras: Magnetospheric or solar wind origin?
• The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs
• The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence?
• Timing Analysis of the Periodic Radio and Optical Brightness Variations of the Ultracool Dwarf, TVLM 513-46546
• K2 Ultracool Dwarfs Survey I: Photometry of an L Dwarf Superflare
• Weather on Other Worlds. III. A Survey for T Dwarfs with High Amplitude Optical Variability
• Radio Constraints on Activity in Young Brown Dwarfs
• Calibrating Ultracool Dwarfs: Optical Template Spectra, Bolometric Corrections, and $\chi$ Values
• The Deepest Constraints on Radio and X-ray Magnetic Activity in Ultracool Dwarfs from WISE J104915.57-531906.1
• Low-resolution optical spectra of ultracool dwarfs with OSIRIS/GTC
• WISEP J060738.65+242953.4: A Nearby. Pole-On L8 Brown Dwarf with Radio Emission
• Long-term, Multiwavelength Light Curves of Ultra-Cool Dwarfs: II. The evolving Light Curves of the T2.5 SIMP 0136 & the Uncorrelated Light Curves of the M9 TVLM 513
• Long-term, Multiwavelength Light Curves of Ultra-cool Dwarfs: I. An Interplay of Starspots & Clouds Likely Drive the Variability of the L3.5 dwarf 2MASS 0036+18

Cited by in corpus (13)

• Let the Great World Spin: Revealing the Stormy, Turbulent Nature of Young Giant Exoplanet Analogs with the Spitzer Space Telescope
• ASKAP Detection of Periodic and Elliptically Polarized Radio Pulses from UV Ceti
• Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
• Direct radio discovery of a cold brown dwarf
• Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey
• Multi-Epoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components
• The Størmer problem for an aligned rotator
• Plausible association of distant late M dwarfs with low-frequency radio emission
• Detection of coherent low-frequency radio bursts from weak-line TTauri stars
• A huge-amplitude white-light superflare on a L0 brown dwarf discovered by GWAC survey
• Ultra-Wideband, Multi-epoch Radio Study of the First Discovered `Main sequence Radio Pulse emitter' CU Vir
• Optical Variability, Rotation Period and Inclination Angle of the M9.5 dwarf BRI 0021-0214
• Radio Emission from UV Cet: Auroral Emission from a Stellar Magnetosphere