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SOLAR AND STELLAR MAGNETIC ACTIVITY C . J . SCHRIJVER C . ZWAAN CAMBRIDGE UNIVERSITY PRESS This timely volume provides the first comprehensive review and synthesis of the currentunderstandingoftheorigin,evolution,andeffectsofmagneticfieldsintheSun andothercoolstars.Magneticactivityresultsinawealthofphenomena–including starspots,nonradiativelyheatedouteratmospheres,activitycycles,decelerationof rotationrates,andeven,inclosebinaries,stellarcannibalism–allofwhicharecovered clearlyandauthoritatively. Thisbookbringstogetherforthefirsttimerecentresultsinsolarstudies,with theirwealthofobservationaldetail,andstellarstudies,whichallowthestudyofhow activityevolvesanddependsonthemass,age,andchemicalcompositionofstars. Theresultisanilluminatingandcomprehensiveviewofstellarmagneticactivity.Ob- servationaldataareinterpretedbyusingthelatestmodelsinconvectivesimulations, dynamo theory, outer-atmospheric heating, stellar winds, and angular momentum loss. Researchersareprovidedwithastate-of-the-artreviewofthisexcitingfield,and thepedagogicalstyleandintroductorymaterialmakethebookanidealandwelcome introductionforgraduatestudents. Cambridgeastrophysicsseries Serieseditors AndrewKing,DouglasLin,StephenMaran,JimPringleandMartinWard Titlesavailableinthisseries 7. SpectroscopyofAstrophysicalPlasmas byA.DalgarnoandD.Layzer 10. QuasarAstronomy byD.W.Weedman 17. MolecularCollisionsintheInterstellarMedium byD.Flower 18. PlasmaLoopsintheSolarCorona byR.J.Bray,L.E.Cram,C.J.DurrantandR.E.Loughhead 19. BeamsandJetsinAstrophysics editedbyP.A.Hughes 20. TheObservationandAnalysisofStellarPhotospheres byDavidF.Gray 21. AccretionPowerinAstrophysics2ndEdition byJ.Frank,A.R.KingandD.J.Raine 22. Gamma-rayAstronomy2ndEdition byP.V.RamanaMurthyandA.W.Wolfendale 23. TheSolarTransitionRegion byJ.T.Mariska 24. SolarandStellarActivityCycles byPeterR.Wilson 25. 3K:TheCosmicMicrowaveBackgroundRadiation byR.B.Partridge 26. X-rayBinaries byWalterH.G.Lewin,JanvanParadijsandEdwardP.J.vandenHeuvel 27. RRLyraeStars byHoraceA.Smith 28. CataclysmicVariableStars byBrianWarner 29. TheMagellanicClouds byBengtE.Westerlund 30. GlobularClusterSystems byKeithM.AshmanandStephenE.Zepf 31. PulsarAstronomy2ndEdition byAndrewG.LyneandFrancisGraham-Smith 32. AccretionProcessesinStarFormation byLeeW.Hartmann 33. TheOriginandEvolutionofPlanetaryNebulae bySunKwok 34. SolarandStellarMagneticActivity byCarolusJ.SchrijverandCornelisZwaan SOLAR AND STELLAR MAGNETIC ACTIVITY C. J. SCHRIJVER Stanford-LockheadInstituteforSpaceResearch,PaloAlto C. ZWAAN AstronomicalInstitute,UniversityofUtrecht PUBLISHED BY CAMBRIDGE UNIVERSITY PRESS (VIRTUAL PUBLISHING) FOR AND ON BEHALF OF THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE The Pitt Building, Trumpington Street, Cambridge CB2 IRP 40 West 20th Street, New York, NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia http://www.cambridge.org © Cambridge University Press 2000 This edition © Cambridge University Press (Vitrtual Publishing) 2003 First published in printed format 2000 A catalogue record for the original printed book is available from the British Library and from the Library of Congress Original ISBN 0 521 58286 5 hardback ISBN 0 511 00960 7 virtual (netLibrary Edition) DieSonneto¨ntnachalterWeise InBruderspha¨renWettgesang, UndihrevorgeschriebeneReise VollendetsiemitDonnergang. IhrAnblickgibtdenEngelnSta¨rke, WennKeinerSieergru¨ndenmag. DieunbegreiflichhohenWerke SindherrlichwieamerstenTag. JohannWolfgangvonGoethe Contents Preface pagexiii 1 Introduction:solarfeaturesandterminology 1 2 Stellarstructure 10 2.1 Globalstellarstructure 10 2.2 Convectiveenvelopes:classicalconcepts 14 2.3 Radiativetransferanddiagnostics 19 2.4 Stellarclassificationandevolution 38 2.5 Convectioninstellarenvelopes 45 2.6 Acousticwavesinstars 60 2.7 Basalradiativelosses 65 2.8 Atmosphericstructurenotaffectedbymagneticfields 70 3 Solardifferentialrotationandmeridionalflow 73 3.1 Surfacerotationandtorsionalpatterns 74 3.2 Meridionalandotherlarge-scaleflows 77 3.3 Rotationwithdepth 79 4 Solarmagneticstructure 82 4.1 Magnetohydrodynamicsinconvectiveenvelopes 83 4.2 Concentrationsofstrongmagneticfield 92 4.3 Magnetohydrostaticmodels 98 4.4 Emergenceofmagneticfieldandconvectivecollapse 105 4.5 Omegaloopsandtoroidalfluxbundles 108 4.6 Weakfieldandthemagneticdichotomy 110 5 Solarmagneticconfigurations 115 5.1 Activeregions 115 5.2 Thesequenceofmagnetoconvectiveconfigurations 126 5.3 Fluxpositioninganddynamicsonsmallscales 126 5.4 Theplagestate 132 5.5 Heattransferandmagneticconcentrations 137 ix x Contents 6 Globalpropertiesofthesolarmagneticfield 138 6.1 Thesolaractivitycycle 138 6.2 Large-scalepatternsinfluxemergence 143 6.3 Distributionofsurfacemagneticfield 155 6.4 Removalofmagneticfluxfromthephotosphere 167 7 Thesolardynamo 173 7.1 Mean-fielddynamotheory 174 7.2 Conceptualmodelsofthesolarcycle 178 7.3 Small-scalemagneticfields 182 7.4 Dynamosindeepconvectiveenvelopes 184 8 Thesolarouteratmosphere 186 8.1 Topologyofthesolarouteratmosphere 186 8.2 Thefilament-prominenceconfiguration 197 8.3 Transients 199 8.4 Radiativeandmagneticfluxdensities 209 8.5 Chromosphericmodeling 217 8.6 Solarcoronalstructure 220 8.7 Coronalholes 227 8.8 Thechromosphere–coronatransitionregion 229 8.9 Thesolarwindandthemagneticbrake 231 9 Stellarouteratmospheres 238 9.1 Historicalsketchofthestudyofstellaractivity 238 9.2 Stellarmagneticfields 238 9.3 TheMt.WilsonCaIIHKproject 242 9.4 Relationshipsbetweenstellaractivitydiagnostics 246 9.5 Thepower-lawnatureofstellarflux–flux relationships 252 9.6 Stellarcoronalstructure 258 10 Mechanismsofatmosphericheating 266 11 Activityandstellarproperties 277 11.1 ActivitythroughouttheH–Rdiagram 277 11.2 Measuresofatmosphericactivity 281 11.3 Dynamo,rotationrate,andstellarparameters 283 11.4 Activityinstarswithshallowconvectiveenvelopes 291 11.5 Activityinverycoolmain-sequencestars 294 11.6 MagneticactivityinTTauriobjects 296 11.7 Long-termvariabilityofstellaractivity 299 12 Stellarmagneticphenomena 303 12.1 Outer-atmosphericimaging 303 12.2 Stellarplages,starspots,andprominences 305 Contents xi 12.3 Theextentofstellarcoronae 310 12.4 Stellarflares 312 12.5 Directevidenceforstellarwinds 314 12.6 Large-scalepatternsinsurfaceactivity 318 12.7 Stellardifferentialrotation 319 13 Activityandrotationonevolutionarytimescales 324 13.1 Theevolutionofthestellarmomentofinertia 324 13.2 Observedrotationalevolutionofstars 326 13.3 Magneticbrakingandstellarevolution 329 14 Activityinbinarystars 336 14.1 Tidalinteractionandmagneticbraking 336 14.2 Propertiesofactivebinaries 340 14.3 Typesofparticularlyactivestarsandbinarysystems 342 15 Propositionsonstellardynamos 344 AppendixI: Unitconversions 351 Bibliography 353 Index 375 Image taken with TRACE in its 171-A˚ passband on 26 July 1998, at 15:50:23 UT of ActiveRegion8,272atthesouthwestlimb,rotatedover−90◦.High-archingloopsare filled with plasma at ∼1MK up to the top. Most of the material is concentrated near thelowerendsundertheinfluenceofgravity.Hotter3–5MKloops,atwhichthebulk oftheradiativelossesfromthecoronaoccur,donotshowupatthiswavelength.Their existence can be inferred from the emission from the top of the conductively heated transition region, however, where the temperature transits the 1-MK range, as seen in the low-lying bright patches of “moss.” A filament-prominence configuration causes extinctionoftheextreme-ultravioletradiation.