Auroral Radio Emission from Ultracool Dwarfs: a Jovian Model

Abstract

A number of fast-rotating ultra cool dwarfs (UCDs) emit pulsed coherent radiation, attributed to the electron cyclotron maser instability, a phenomenon that occurs in the solar system at planets with strong auroral emission. In this paper we examine magnetosphere-ionosphere coupling currents in UCDs, adopting processes used in models of Jovian emission. We consider the angular velocity gradient arising from a steady outward flux of angular momentum from an internal plasma source, as analogous to the jovian main oval current system, as well as the interaction of a rotating magnetosphere with the external medium. Both of these mechanisms are seen in the solar system to be responsible for the production of radio emission. We present the results of an investigation over a range of relevant plasma and magnetosphere-ionosphere coupling parameters to determine regimes consistent with observed UCD radio luminosities. Both processes are able to explain observed UCD luminosities with ionospheric Pedersen conductances of ~1-2 mho, either for a closed magnetosphere with a plasma mass outflow rate of ~10${}^5$ kg/s, i.e. a factor of ~100 larger than that observed at Jupiter's moon Io, or for a dwarf with an open magnetosphere moving through the interstellar medium at ~50 km/s and a plasma mass outflow rate of ~1000 kg/s. The radio luminosity resulting from these mechanisms have opposing dependencies on the magnetic field strength, a point which may be used to discriminate between the two models as more data become available.

arXiv comment12 pages, 10 figures

References in corpus (26)

• Simulations of dynamo action in fully convective stars
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• Magnetic field generation in fully convective rotating spheres
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Flaring Up All Over -- Radio Activity in Rapidly-Rotating Late-Type M and L Dwarfs
• Predicting low-frequency radio fluxes of known extrasolar planets
• 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?
• Auroral radio emission from late L and T dwarfs: A new constraint on dynamo theory in the substellar regime
• The Radio Activity-Rotation Relation of Ultracool Dwarfs
• Periodic Radio and H-alpha Emission from the L Dwarf Binary 2MASSW J0746425+200032: Exploring the Magnetic Field Topology and Radius of an L Dwarf
• The Arecibo Detection of the Coolest Radio-flaring Brown Dwarf
• Origin of electron cyclotron maser-induced radio emissions at ultra-cool dwarfs: magnetosphere-ionosphere coupling currents
• Magnetosphere-ionosphere coupling at Jupiter-like exoplanets with internal plasma sources: implications for detectability of auroral radio emissions
• Stellar wind-magnetosphere interaction at exoplanets: computations of auroral radio powers
• Wideband Dynamic Radio Spectra of Two Ultra-cool dwarfs
• The Rotation Period and Magnetic Field of the T Dwarf 2MASSI J1047539+212423 Measured From Periodic Radio Bursts
• Volume-limited radio survey of ultracool dwarfs
• Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
• Radio Flaring from the T6 Dwarf WISEPC J112254.73+255021.5 with A Possible Ultra-short Periodicity
• A Mini-survey of Ultracool Dwarfs at 4.9 GHz
• Radio detections of southern ultracool dwarfs
• On a transition from solar-like coronae to rotation-dominated jovian-like magnetospheres in ultracool main-sequence stars
• Comparative analysis of two formation scenarios of bursty radio emission from ultracool dwarfs
• Modelling the radio pulses of an ultracool dwarf
• A LOFAR mini-survey for low-frequency radio emission from the nearest brown dwarfs

Cited by in corpus (20)

• Coherent radio emission from a quiescent red dwarf indicative of star-planet interaction
• The Strongest Magnetic Fields on the Coolest Brown Dwarfs
• Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
• Resolved imaging of an extrasolar radiation belt around an ultracool dwarf
• Direct radio discovery of a cold brown dwarf
• The CARMENES search for exoplanets around M dwarfs: Stable radial-velocity variations at the rotation period of AD~Leonis -- A test case study of current limitations to treating stellar activity
• Fine structures of radio bursts from flare star AD Leo with FAST observations
• Brown dwarfs as ideal candidates for detecting UV aurora outside the Solar System: Hubble Space Telescope observations of 2MASS J1237+6526
• The TESS View of LOFAR Radio-Emitting Stars
• Polarised radio pulsations from a new T dwarf binary
• Magnetohydrodynamic modelling of star-planet interaction and associated auroral radio emission
• A Deep Radio Limit for the TRAPPIST-1 System
• The UV spectrum of the Ultracool Dwarf LSR J1835+3259 observed with the Hubble Space Telescope
• The Occurrence Rate of Quiescent Radio Emission for Ultracool Dwarfs using a Generalized Semi-Analytical Bayesian Framework
• Radio Emission from Binary Ultracool Dwarf Systems
• Location and energy of electrons producing the radio bursts from AD Leo observed by FAST in December 2021
• Differences in radio emission from similar M dwarfs in the binary system Ross 867-8
• Transitions in magnetic behavior at the substellar boundary
• Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf
• Simulations of Electron Beam Interactions in Brown Dwarf Atmospheres