title: Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence.
abstract: Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.
authors.affiliation: California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: G
authors.initials: G
authors.lastname: Hallinan
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK.
authors.forename: S P
authors.initials: SP
authors.lastname: Littlefair
authors.affiliation: Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK.
authors.forename: G
authors.initials: G
authors.lastname: Cotter
authors.affiliation: California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: S
authors.initials: S
authors.lastname: Bourke
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109-0899, USA.
authors.forename: L K
authors.initials: LK
authors.lastname: Harding
authors.affiliation: California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Pineda
authors.affiliation: Centre for Astronomy, National University of Ireland, Galway, University Road, Galway, Republic of Ireland.
authors.forename: R P
authors.initials: RP
authors.lastname: Butler
authors.affiliation: Department of Mathematical Sciences, Yeshiva University, New York, New York 10033, USA.
authors.forename: A
authors.initials: A
authors.lastname: Golden
authors.affiliation: Astronomy Department, University of California, Campbell Hall, Berkeley, California 94720, USA.
authors.forename: G
authors.initials: G
authors.lastname: Basri
authors.affiliation: Armagh Observatory, College Hill, Armagh BT61 9DG, UK.
authors.forename: J G
authors.initials: JG
authors.lastname: Doyle
authors.affiliation: California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Kao
authors.affiliation: Kiepenheuer Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg, Germany.
authors.forename: S V
authors.initials: SV
authors.lastname: Berdyugina
authors.affiliation: Institute of Solar-Terrestrial Physics, Irkutsk 664033, Russia.
authors.forename: A
authors.initials: A
authors.lastname: Kuznetsov
authors.affiliation: National Radio Astronomy Observatory, PO Box O, Socorro, New Mexico 87801, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Rupen
authors.affiliation: Department of Astronomy, Faculty of Physics, St Kliment Ohridski University of Sofia, 5 James Bourchier Boulevard, 1164 Sofia, Bulgaria.
authors.forename: A
authors.initials: A
authors.lastname: Antonova