SuperflaresonSun-likeStars

KazunariShibataKwasanandHidaObservatories,KyotoUniversity,Kyoto,Japan

MAXIsymposiumDec6,2016Riken,Wako,Saitama13:55-14:25invited

Collaborators:HiroyukiMaehara,TakuyaShibayama,YutaNotsu,ShotaNotsu,SatoshiHonda,DaisakuNogami,TakuyaTakahashi,HiroakiIsobe

IntroducTontoSolarFlares

KojikiandtheUniverse(古事記と宇宙）

Kitaro　andShibata

Specialentertainment

Let’senjoyVariousmoviesofSolarflaresandErupTonswithKitaro-san’sMusicKojiki:Orochi(7min)

Orochiis8headeddragonmonster

StellarFlares

Totalenergyofstellarflares

SuperflaresTheirenergy=10-10^6Tmesthatofthelargestsolarflares

Solarflares

Solarmicroflares

Stellarflares

TheirhoststarsareyoungstarsandbinarystarswithfastrotaTon

(Feldman+1995,Koyama+1996,Tsuboi+1998,Ozawa+1999,Hamaguchi+2000,Imanishi+2001)

ShibataandYokoyama(2002)

Q:Whatdeterminesflaretotalenergy?A:looplength(becausemagneTcfieldstrengthis

roughlyconstant)

Thereasonwhystellarflaresarehot=>looplengthsofstellarflaresarelarge

ShibataandYokoyama(2002)

CfIsobeetal.2003,Aulanieretal.2013

Whyyoungstarsproducesuperflares?

•  Answer：youngstar’srotaTonisfast（sodynamoisacTveandtotalmagneTcfluxislarge=>loopislarge）

Youngstars

StellarX-rayLuminosity

StellarrotaTonalvelocity

Youngstars

Agedstars(Sun)）

Agedstars(Sun)

QuesTons•  Previously,ithasbeenbelievedthattheSundoesnot

producesuperflares(>10^33erg),becausetheSunisoldandisslowlyrotaTng.

•  However,　Schaeferetal.(2000)discovered9superflaresonordinarysolartypestarswithslowrotaTon.

•  Schaeferetal.arguedthattheSunwouldneverproducesuperflares,becausetheybelievedthathotJupiterisanecessarycondiTontoproducesuperflares.

•  Aresuperflaresreallyoccurringonordinarysolartypestars?

•  ArehotJupitersnecessarycondiTonforsuperflares?

SuperflaresonSolarTypeStars

Maeharaetal.(2012)Nature,483,478

superflare

nanoflare microflare

solar flare

staTsTcsofoccurrencefrequencyofsolarflares,microflares,nanoflares

1000in1year100in1year10in1year1in1year1in10year1in100year1in1000year1in10000year

CMXX10X1000X100000

？

Largestsolarflare

superflares

HowcanweobservesuperflaresontheSun?

•  IfempiricalstaTsTcsruleofsolarflaresisappliedtomuchlargerflares(superflares),thenthefrequencyofsuperflareswithenergy1000Tmeslargerthanthelargestsolarflaresmightoccuroncein10000years.

•  However,theperiodofmodernobservaTonsoftheSunwithtelescopeisonly400years.

•  HowcanweobservetheSunfor10000years?

•  Ifweobserve10000solartypestars(similartoourSun)for1year,wecangetthedatasimilartothedataobtainedfrom10000yearsobservaTonsoftheSun!

ProfSekiguchikindlytoldmethattheKeplersatelliteistakingsuchdata!

Keplersatellite(NASA)•  Spacemissiontodetectexoplanetsbyobservingtransitofexoplanets

•  0.95mtelescope•  Observing160,000starsconTnuously(from2009to2013).Amongthem,80000aresolartypestars.

•  ~30minTmecadence(publicdata)

•  HencewesearchedforsuperflaresonsolartypestarsusingKeplersatellitedata,whichincludedataof83000solartypestars

•  Sincethedataaresolarge,weasked1styearundergraduatestudentstohelpanalyzingthesestars,becausestudentshavealotoffreeTme(2010fall)

•  Surprisingly,we(they)found365superflareson148solartypestars(G-typemainsequencestars)

SuperflaresonSolarTypeStars:Ourstudy(Maeharaetal.2012)

SuperflaresonSolartypestars

H.Maehara,T.Shibayama,S.Notsu,Y.Notsu,T.Nagao,S.Kusaba,S.Honda,D.Nogami,K.Shibata

 

PublishedinNature(2012,May)

Undergraduatestudents

typicalsuperflareobservedbyKepler

Brightnessofastarandaflare

Time(day)

Totalenergy~10^35erg

Maeharaetal.(2012)

typicalsuperflareobservedbyKepler

Brightnessofastarandaflare

Time(day)

Totalenergy~10^36erg

Maeharaetal.(2012)

WhatisthecauseofstellarbrightnessvariaTon?

ItislikelyduetorotaTonofastarwithabigstarspot

ModelcalculaTonofstellarbrightnessvariaTonKIC6034120

2％(

平均基準)

model(green)inclinaTon=45°Starspotradius0.16R*

5daysNotsuetal.Tme

Stellarbrightness

KIC6034120

2％(

平均基準) 5days

Notsuetal.

ModelcalculaTonofstellarbrightnessvariaTon

model(green)inclinaTon=45°Starspotradius0.16R*

Tme

Stellarbrightness

FlareenergyvsrotaTonalperiod

Starswithperiodlongerthan10dayscfsolarrotperiod~25days

Maehara+(2012),　Notsu+(2013)

FastrotaTon(young)

SlowrotaTon(old)

SolarRotaTon

ThereisnohotJupiterinthesesuperflarestarsagainstpreviouspredicTon(Schaefer+2000)

25days

Whatisthefrequencyofsuperflares?(NotsuY+2013)

RotaTonalPeriod(days)

Num

bero

fsupe

rflaresperyear

perstar

SolarRotaTon

FastrotaTon(young)

SlowrotaTon(old)

25days

Flarefrequencyvs.rotaTonperiod

•  ThefrequencyofsuperflaresdecreasesastherotaTonperiodincreases(P>2-3days).–  Thefrequencyofsuperflaresshowsthe“saturaTon”foraperiodrange<2-3days.

G-dwarfs, Eflare > 5×1034 erg

Notsuetal.(2013)

(Ro=P_rot/t_conv)RotaTonalPeriod(days)

superflare

nanoflare microflare

solar flare

ComparisonofstaTsTcsbetweensolarflares/microflaresandsuperflares

？

Largestsolarflare

Shibataetal.2013

superflare

nanoflare microflare

solar flare

ComparisonofstaTsTcsbetweensolarflares/microflaresandsuperflares

1000in1year100in1year10in1year1in1year1in10year1in100year1in1000year1in10000year

CMXX10X1000X100000

Largestsolarflare

Superflaresof1000TmesmoreEnergeTcthanthelargestsolarflaresoccuroncein5000years!

Shibataetal.2013

10^35ergX10000

su

10^34ergX1000

10^33ergX100

10^32ergX10

10^31erg　X

10^30ergM

10^29erg　C

0.0001 0.001

0.01

Flareenergyvssunspotarea

Oncein1000years

Oncein10years

Oncein100years

Oncein1year

10in1year

100in1year

1000in1year

Sunspotarea(inunitofsolarsurfacearea)

Solarflare

Superflaresonsolartypestars

Sammisetal.2000

FlareEnergy

10^35ergX10000

su

10^34ergX1000

10^33ergX100

10^32ergX10

10^31erg　X

10^30ergM

10^29erg　C

Flareenergyvssunspotarea

Oncein1000years

Oncein10years

Oncein100years

Oncein1year

10in1year

100in1year

1000in1year

Sunspotarea(inunitofsolarSurfacearea)

Superflaresonsolartypestars

Sammisetal.2000

0.0001 0.001

Solarflare

0.01

FlareEnergy

Solarflares

Flareenergyvssunspotarea(magneTcflux)

2/3

219

2

332

2/3232

103101.0][107

88

⎟⎟⎠

⎞⎜⎜⎝

⎛

×⎟⎠

⎞⎜⎝

⎛⎟⎠

⎞⎜⎝

⎛×≈

≈≈≈

cmA

GBferg

ABfLBffEE

spot

spotmagflare ππ

Shibataetal.(2013)

?

Solarflares

Stellarflares

SpectroscopicObservaTonsofSuperflareStars

Notsuetal.(2015)PASJ

Projected rotation velocity (v sin i)

※Measurement methods Takeda et al.(2008etc)

Lineofsight

i

RotaKonAxis

Fast rotators ⇒ wide line profile

Slow rotators ⇒ narrow line profile

We can estimate projected rotation velocity (v sin i) from the Doppler broadening of absorption lines.

Notsu,Y.etal.(2015)

Rotation Period ⇔Brightness variation period ? Most of the data points are below the line of i=90°

⇒“Brightness variation≒Rotation” is OK!!

PRv star

lcπ2

≈※Sun: Vrot～2 [km s-1]

Velocity estimated from brightness variation period (Vlc[km s-1])

v sin i [km s-1]

Pole-onview

pole-onview

Edge-onview(sini=1)

LineofSight

i

RotaKonAxis

Notsu,Y.etal.(2015)

Flareenergyvs.areaofstarspots

lowinclinaTonangle

Notsu,Y.etal.(2015)

SpectroscopicrotaTonalvelocity　(Subaruobs)

PhotometricrotaTonalvelocity

Solarflares

Stellarflares

Okayama3.8mNewTechnologyTelescopeofKyotoUniv(underconstrucKon)

courtesyofProf.Nagata(DepartmentofAstronomy,KyotoUniversity)

HighspeedphotometricandspectroscopicobservaTonofTransientobjectsGammarayburstsExoplanetsStellarflares(superflares)

Willbecompleted~2017

SpectroscopicObservaTonsofSolartypestarscausingsuperflareswillbeextremelyimportant

NewTechnology1.MakingMirrorswithGrinding2.Segmentedmirror3.UltraLightmounTng

BudgetforoperaTonIssTlllacking.Pleasesupportus!

Summary•  UsingKeplerdata,wefound365superflares(10^33-10^36erg)on148

solartypestars(among80000stars)during120days(Maehara+2012).=>1547superflaresfrom279solartypestarsduring500days(Shibayama+2013).

•  SuperflaresoccuronSun-likestars(5600-6000KandslowrotaTon)withfrequencysuchthatsuperflareswithenergy10^33-10^35erg(X100-X10000solarflare)occuroncein500-5000years

•  Thesestarshavelargestarspot(Notsu+2013).•  RotaTonalvelocityandlargestarspotof34superflarestarshasbeen

confirmedbyspectroscopicobservaTons(Notsu+2015)

•  SimultaneousX-rayandopTcalobservaTonsofthesesuperflareswouldbeextremelyimportant!

ThankyouforyouraxenTon