J/A+A/682/A170ivo://CDS.VizieR/J/A+A/682/A170doi:10.26093/cds/vizier.36820170CDSBloot S.Callingham J.R.Vedantham H.K.Kavanagh R.D.Pope B.J.S.,Climent J.B.Guirado J.C.Pena-Monino L.Perez-Torres M.2024-11-28T20:06:23Z2024-02-22T09:06:32ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frvariable-starsradio-continuum-emissionmagnetic-fieldsspectroscopyStellar radio emission can measure a star's magnetic field strength and structure, plasma density, and dynamics, and the stellar wind pressure impinging on exoplanet atmospheres. However, properly interpreting the radio data often requires temporal baselines that cover the rotation of the stars, orbits of their planets, and any longer-term stellar activity cycles. Here we present our monitoring campaign on the young, active M dwarf AU Microscopii with the Australia Telescope Compact Array between 1.1 and 3.1GHz. With over 250 hours of observations, these data represent the longest radio monitoring campaign on a single main-sequence star to date. We find that AU Mic produces a wide variety of radio emission, for which we introduce a phenomenological classification scheme predicated on the polarisation fraction and time-frequency structure of the emission. Such a classification scheme is applicable to radio emission from other radio-bright stars. The six types of radio emission detected on AU Mic can be broadly categorised into five distinct types of bursts, and broadband quiescent emission. We find that the radio bursts are highly circularly polarised and periodic with the rotation period of the star, implying that the emission is beamed. It is therefore most likely produced by the electron cyclotron maser instability. We present a model to show that the observed pattern of emission can be explained by emission from auroral rings on the magnetic poles. The total intensity of the broadband emission is stochastic, but we show that its circular polarisation fraction is also periodic with the rotation of the star. Such a periodicity in the polarised fraction of emission has not been observed on an M dwarf before. We present a qualitative model to describe the periodicity in the polarisation fraction of the broadband emission, using low-harmonic gyromagnetic emission. Using a simple qualitative model, we infer a magnetic obliquity of at least 20 degrees from the observed variation in polarisation fraction. Finally, we show that the radio emission might be evolving on long timescales, hinting at a potential stellar magnetic activity cycle.2024A&A...682A.170Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/682/A170CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/654/A159 : CHEOPS photometry of Au Mic b transits in 2020 (Szabo+, 2021)J/A+A/659/L7 : AU Mic b and c transits with CHEOPS (Szabo+, 2022)J/AJ/162/137 : Minerva-Australis radial velocity of AU Mic (Addison+, 2021)J/AJ/164/110 : HST/COS far-UV spectra of AU Microscopii flareshttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/682/A170https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/682/A170http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/682/A170https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/682/A170https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/682/A170http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/682/A170GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/A+A/682/A170/table1Summary of the observations used in this workrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochEpoch (YYYY-MM-DD)time.epochnullablen_Epoch[*y] Note on Epoch (1)meta.notecharArrayArray configurationphys.atmol.configuration;instr.setupcharDurDurationhtime.durationfloatFileSIName of Stokes I flux density datafile in subdirectory dynsp (2)meta.id;meta.filecharFileSIiName of Stokes I imaginary component datafile in subdirectory dynsp (2)meta.id;meta.filecharFileSVName of Stokes V flux density datafile in subdirectory dynsp (2)meta.id;meta.filecharFileSViName of Stokes V imaginary component datafile in subdirectory dynsp (2)meta.id;meta.filecharJ/A+A/682/A170/burstThe maximum flux density of each Stokes V burst detectedrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochEpochtime.epochnullableSBurst flux densitymJyphot.flux.density;em.radiodoubleJ/A+A/682/A170/listList of fits filesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNxNumber of pixels along X-axismeta.numberintNyNumber of pixels along Y-axismeta.numberintsizeSize of FITS fileKibytephys.size;meta.fitsintLCShow the light curvemeta.ref.urlcharFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar