magnetic activity on rapidly rotating stars i: surface flux distributions

Andrew Collier Cameron, Moira Jardine, John Barnes, Sandra Jeffers, Duncan Mackay, Kenny Wood(University of St Andrews)Jean-François Donati (Obs. Midi-Pyrenees, Toulouse).Meir Semel (Obs. de Paris, Meudon)

Magnetic activity on rapidly Magnetic activity on rapidly rotating stars I: Surface flux rotating stars I: Surface flux

distributions distributions • Activity proxies Activity proxies • Surface coverage Surface coverage

of active regionsof active regions• Polar spotsPolar spots• Diffusion and Diffusion and

advection of advection of surface magnetic surface magnetic fieldsfields

• Filling factors and Filling factors and flux emergence flux emergence rates.rates.

OverviewOverview

• Why are rapidly rotating stars useful?Why are rapidly rotating stars useful?• We can: We can:

– map their surfaces!map their surfaces!– determine the latitude distribution of active regionsdetermine the latitude distribution of active regions– estimate the flux emergence rate and spot lifetimeestimate the flux emergence rate and spot lifetime– map the magnetic polarity distribution in the map the magnetic polarity distribution in the

networknetwork

• What does this all tell us about dynamos?What does this all tell us about dynamos?– Spectral-type dependence of surface flux Spectral-type dependence of surface flux

distributiondistribution– Spectral-type dependence of differential rotationSpectral-type dependence of differential rotation– Cyclic behaviour: spot coverage, differential Cyclic behaviour: spot coverage, differential

rotationrotation– Meridional circulation?Meridional circulation?

Magnetic activity proxies Magnetic activity proxies • Broad-band optical modulation Broad-band optical modulation

– => dark starspots=> dark starspots

Collier Cameron et al 1999 Kürster et al 1997

Magnetic activity proxies Magnetic activity proxies • Emission cores in strong UV/optical lines Emission cores in strong UV/optical lines

– => chromospheres=> chromospheres

Linsky et al 1979Sun in Ca II 393.3 nm filter


chromosphereschromospheres rotation periodsrotation periods activity cyclesactivity cycles

Vaughan et al 1981

Magnetic activity proxies Magnetic activity proxies • Emission cores in strong Emission cores in strong

UV/optical lines UV/optical lines chromosphereschromospheres rotation periodsrotation periods activity cyclesactivity cycles differential rotation?differential rotation?

– Secular changes in Ω Secular changes in Ω range of surface range of surface rotation rates.rotation rates.– Period-DR relation:Period-DR relation:

– BUT: No reliable latitude BUT: No reliable latitude informationinformation

Donahue, Saar & Baliunas 1996

€

ΔP∝ P1.3±0.1


chromosphereschromospheres rotation periodsrotation periods activity cyclesactivity cycles dynamos?dynamos?

Noyes et al 1984

Magnetic activity proxies Magnetic activity proxies • Soft X-ray emission Soft X-ray emission

magnetically confined coronal plasmamagnetically confined coronal plasma

XMM spectrum and light-curve of star in IC2391 (Marino et al 2003)


“ “Saturation” …Saturation” …

Vilhu 1984


“ “Saturation” …Saturation” … and “super-saturation”and “super-saturation”

Prosser et al. 1996, alpha Persei cluster Stauffer et al. 1997

Magnetic activity proxies Magnetic activity proxies • Decrease in rotation with age Decrease in rotation with age

– Ultra-fast rotators found in young clusters onlyUltra-fast rotators found in young clusters only– Earlier spectral types spin faster after ~0.3 GyrEarlier spectral types spin faster after ~0.3 Gyr– => Hot magnetically channelled winds dΩ/dt ~ -Ω=> Hot magnetically channelled winds dΩ/dt ~ -Ω33

Barnes, S. 2001

Barnes, S. 2001Barnes, S. 2001

Convection and rotation Convection and rotation • F, G, K, M spectral types F, G, K, M spectral types

outer convective zonesouter convective zones

• Activity indicators increase with rotation Activity indicators increase with rotation Rotation drives activityRotation drives activity

• Evidence of differential rotation: can we map Evidence of differential rotation: can we map it?it?

• Spindown rates depend on spectral typeSpindown rates depend on spectral type Convection zone depth is importantConvection zone depth is important

• Do young stars really have up to 50% starspot Do young stars really have up to 50% starspot occupancy?occupancy?

• For the fastest rotators LFor the fastest rotators Lxx decreases with Ω ! decreases with Ω !

Evidence for dense spot Evidence for dense spot coveragecoverage

• TiO bands occur in TiO bands occur in spots only.spots only.

O’Neal, Neff & Saar 1996



• 7055Å/8860Å band 7055Å/8860Å band ratio gives spot ratio gives spot temperature.temperature.





• Band strength gives Band strength gives spot covering spot covering fraction.fraction.


Compositemodelspectrum

Spot filling factor

Continuumbrightness ratio

Normalisedspotspectrum

Normalisedphotosphericspectrum




• Band strength gives Band strength gives spot covering spot covering fraction.fraction.

• Active stars have Active stars have filling factors filling factors ffss~20% to 40%~20% to 40%


Measuring spot coverage with Measuring spot coverage with HSTHST

• Eclipsing binary SV CamEclipsing binary SV Cam• G0V + K5VG0V + K5V• Edge-on orbitEdge-on orbit• K5V transits primaryK5V transits primary• Light-curve analysis Light-curve analysis

radiiradii• Measure missing-flux Measure missing-flux

spectrum at mid eclipsespectrum at mid eclipse• Use HIPPARCOS parallax Use HIPPARCOS parallax

to get solid angle to get solid angle surface brightnesssurface brightness

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Jeffers et al. 2004



Eclipsed-flux deficiency in SV Eclipsed-flux deficiency in SV CamCam

• Eclipsed flux is ~30% less than best-fit TEclipsed flux is ~30% less than best-fit Teffeff indicates.indicates.

• ffSS~40%~40%



Jeffers et al. 2004

Evolutionary effects of flux Evolutionary effects of flux blocking blocking

• Star expands slightlyStar expands slightly

• Photospheric TPhotospheric Teffeff increasesincreases significant effects on HR significant effects on HR

diagrams of young open diagrams of young open clusters, e.g. Pleiadesclusters, e.g. Pleiades

Stauffer et al 2003Spruit & Weiss 1986

Imaging of stellar surfacesImaging of stellar surfaces• Direct imaging?Direct imaging?• Stellar Imager Stellar Imager

mission concept:mission concept:– Goal is 50,000 km Goal is 50,000 km

resolution on a resolution on a Sunlike star 4 pc Sunlike star 4 pc awayaway

– Requires angular Requires angular resolution 60-120 resolution 60-120 µasµas

– 0.5-km space-based 0.5-km space-based UV-optical UV-optical interferometer interferometer array ?array ?

Rotational broadening Rotational broadening of photospheric linesof photospheric lines

• Rotational Doppler Rotational Doppler shift dominates shift dominates broadening of stellar broadening of stellar photospheric lines in photospheric lines in rapid rotators.rapid rotators.

• Rotation profile Rotation profile contains information contains information about surface about surface features (Goncharsky features (Goncharsky et al 1977, Vogt & et al 1977, Vogt & Penrod 1983)Penrod 1983)

€

veq sin i ≈ 2R

Rsun

⎛

⎝ ⎜

⎞

⎠ ⎟

Ω

Ω sun

⎛

⎝ ⎜

⎞

⎠ ⎟sin i km s -1

Stauffer et al 1997

Starspot “bumps” in spectral Starspot “bumps” in spectral lineslines

Intensity

A A

Intensity

v sin i-v sin i v(spot)

Velocity

v sin i-v sin i v(spot)

Velocity

Imaging of stellar Imaging of stellar surfaces on a budgetsurfaces on a budget

• Combine profiles of all Combine profiles of all recorded photospheric lines recorded photospheric lines to boost S:N.to boost S:N.

• Compute synthetic line Compute synthetic line profiles from trial image.profiles from trial image.

• Iterate to target Iterate to target 22 at at maximum entropy.maximum entropy.

• Get simplest image that fits Get simplest image that fits data.data.

• Nearly always get a dark polar Nearly always get a dark polar cap.cap.

Starspotsignatures inphotospheric lines

-v sin i +v sin i

Example: Speedy Mic (K3V)Example: Speedy Mic (K3V)• Spots present at all latitudes including polar Spots present at all latitudes including polar

regions.regions.

Barnes et al 2004

Example: HDE 283572Example: HDE 283572• Strassmeier et al 1998: WTTS, v sin i = 78 km Strassmeier et al 1998: WTTS, v sin i = 78 km

ss–1–1

Polar fieldsPolar fields

• Schrijver & Title (2002) modelled Schrijver & Title (2002) modelled flux emergence on stars of flux emergence on stars of different rotation rates.different rotation rates.

• Rapid rotators develop rings of Rapid rotators develop rings of opposite polarity at poles.opposite polarity at poles.

• Note reversal of polar fields over Note reversal of polar fields over cycle.cycle.

• Also Schüssler (1997) modelled Also Schüssler (1997) modelled buoyant flux tube emergence. buoyant flux tube emergence. Flux tubes deflected to high Flux tubes deflected to high latitudes on rapid rotators.latitudes on rapid rotators.

Andrew Collier Cameron, Moira Jardine, Duncan Mackay, Kenny Wood, John Barnes, Sandra Jeffers(University of St Andrews)Jean-François Donati (Obs. Midi-Pyrenees, Toulouse).Meir Semel (Obs. de Paris, Meudon)

Magnetic activity on rapidly Magnetic activity on rapidly rotating stars II:Temporal rotating stars II:Temporal

evolutionevolution• Tracking starspotsTracking starspots• Time-varying Time-varying

differential differential rotationrotation

• Differential Differential rotation along the rotation along the main sequence main sequence

• Stellar Stellar magnetogramsmagnetograms

• 3D coronal 3D coronal structurestructure

What else can we learn from What else can we learn from stellar surface maps?stellar surface maps?

• Snapshots:Snapshots:– Unpolarized: Latitude distributions of spots Unpolarized: Latitude distributions of spots – Locations of slingshot prominence complexesLocations of slingshot prominence complexes– Circularly polarized: Magnetic topology of coronaCircularly polarized: Magnetic topology of corona

• Days-weeks timescale: Days-weeks timescale: – starspots trace surface differential rotation and meridional starspots trace surface differential rotation and meridional

flowsflows

• Weeks-months:Weeks-months:– Lifetimes of individual spots and magnetic regionsLifetimes of individual spots and magnetic regions

• Years:Years:– Stellar butterfly diagram: Dynamo cyclesStellar butterfly diagram: Dynamo cycles– Polarity reversals?Polarity reversals?

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Polar spots and convective-zone Polar spots and convective-zone depth depth

• LQ Lup (G2)LQ Lup (G2)• Donati et al (2000)Donati et al (2000)


• HE 699 (G2-3V; alpha Per G dwarf)HE 699 (G2-3V; alpha Per G dwarf)• Jeffers et al (2002)Jeffers et al (2002)






• HK Aqr (M1)HK Aqr (M1)• Barnes et al (2004)Barnes et al (2004)






• RE J1816+541 (M1)RE J1816+541 (M1)• Barnes et al (2001)Barnes et al (2001)












G3V G6V G8V K0V K3V

M1V M1V

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Surface brightness: Surface brightness: 1996 Dec 23 - 291996 Dec 23 - 29

• Equator rotatesEquator rotates

faster than polefaster than pole– solar-like shearsolar-like shear– Prot ~ 0.5 d Prot ~ 0.5 d – Equator laps pole by Equator laps pole by

1 cycle every ~ 120d1 cycle every ~ 120d

Surface shear: 1996 December 23 - Surface shear: 1996 December 23 - 2929

• CCF for CCF for surface-surface-brightness brightness images images

• CCF for CCF for magnetic magnetic images:images:

Starspots as Starspots as flow tracersflow tracers

• Individual spot Individual spot trails have their trails have their own recurrence own recurrence periods.periods.

• Velocity Velocity amplitude of amplitude of sinusoid:sinusoid:

K =Ω(θ)R* cosθsini

Rotation rateat latitude

Stellar radius

Axialinclination

Matched-filter analysisMatched-filter analysis• Travelling gaussian:Travelling gaussian:

g(v,t |φ,K,Ω)=

f(γ)Δvl π

exp−v−K sinisinψ −v0

Δvl

⎛

⎝ ⎜

⎞

⎠ ⎟

2⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

K =Ω(θ)R* cosθsini

cosγ =cosisinθ +sinicosθcosψ

f(γ)=cosγ(1−u+ucosγ)

Spot velocity amplitude:

Foreshortening and limb darkening

Inclination Latitude

Spot phase anglerelative to observer’s meridian

Intrinsic line width

Spot rotation rate:

Optimal Optimal scalingscaling

ˆ W =

xi , jgi, j /Var(xi, j )i, j∑

gi, j2 /Var(xi, j )

i, j∑

χ 2 = (xi, j − ˆ W gi, j )2 /Var(xi, j )

i,j∑

gij : equatorial spot at phase 0.5

Badness of fit:

Scale factor:

xij (phase binned on trial period) 2

Optimal Optimal scalingscaling

ˆ W =

xi , jgi, j /Var(xi, j )i, j∑

gi, j2 /Var(xi, j )

i, j∑

χ 2 = (xi, j − ˆ W gi, j )2 /Var(xi, j )

i,j∑

gij : equatorial spot at phase 0.5

Badness of fit:

Scale factor:

xij (phase binned on trial period) 2

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1P(θ)

=1

Pequator

−1

Pbeat

sin2θ

Differential rotation: 1988 DecDifferential rotation: 1988 Dec

• Model fit:Model fit:

1P(θ)

=1

Pequator

−1

Pbeat

sin2θ

Differential rotation: 1992 JanDifferential rotation: 1992 Jan


1P(θ)

=1

Pequator

−1

Pbeat

sin2θ

Differential rotation: 1993 NovDifferential rotation: 1993 Nov


1P(θ)

=1

Pequator

−1

Pbeat

sin2θ



Differential rotation 1988-2001Differential rotation 1988-2001• Differential rotation rate doubled in 3 Differential rotation rate doubled in 3

years from 1988 Dec to 1992 Jan.years from 1988 Dec to 1992 Jan.• As equator speeds up, polar regions slow As equator speeds up, polar regions slow

down.down.• Rotation rate at Rotation rate at ~ 40~ 40oo remains ~ constant. remains ~ constant.

• Plot estimates in Ωeq-dΩ plane

• Interpret differences as:• distinct anchoring depths of tracers within CZ• temporal changes in angular rotation profile within CZ

Impact on convective zonesImpact on convective zones• Angular rotation in convective zoneAngular rotation in convective zone

• plot estimates in Ωeq-dΩ plane

• changes in differential rotation: powered with a few % of L* correspond to a field of ≈10 kG in the whole CZ sufficient to generate orbital period fluctuations of binary stars (Applegate 1992)

Impact on convective zonesImpact on convective zones• Angular rotation in convective zoneAngular rotation in convective zone

Differential rotation Differential rotation along the main sequence along the main sequence

Barnes et al. 2004

Comparison with other Comparison with other techniques techniques

Barnes et al. 2004

Zeeman Doppler ImagingZeeman Doppler Imaging• Zeeman effect:Zeeman effect:

– component: Linear polarization, no component: Linear polarization, no shift shift– components: Elliptical polarization, components: Elliptical polarization, ΔΔ ~ ± ~ ±

gBgB

• Field orientation and line-of-sight:Field orientation and line-of-sight:– Circular polarization (Circular polarization ( cpt) strongest when B cpt) strongest when B

// line of sight.// line of sight.

• How stellar rotation helps:How stellar rotation helps:– Rotational Doppler effect separates magnetic Rotational Doppler effect separates magnetic

regions in velocity space.regions in velocity space.– Field orientation relative to line of sight Field orientation relative to line of sight

changes as magnetic region crosses disc.changes as magnetic region crosses disc.

Landé g-factorfor line

Local magneticfield strength

The Semel The Semel PolarimeterPolarimeter

Aberration-free linear polarizingbeamsplitter

/4 plate

Optical axis switched at ±45o relative to beamsplitter axes

AAT f/8 Cass

focus

Focal

reducer

Dual beams analyzedfor opposite circularpolarization states

Bowen-Walravenimage slicerat UCLES slit position

UCLES

Semel et al 1993: A&A 278, 231

Dual fibre feedto UCLES slit area

Stokes V: weak-field approximationStokes V: weak-field approximation

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

5000 5000.5 5001 5001.5

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

5000 5000.5 5001 5001.5

I () I ()

V () V ()

Left Right

Difference

High g Low g

V loc(v) ∝ g ∂Iloc(v)∂v

, v=cΔ

Multi-line imagingMulti-line imaging• Essential for ZDI Essential for ZDI

– Stokes V signature is typically < 10Stokes V signature is typically < 10–4–4 times continuum. times continuum.– Typical S:N is 300 in continuum.Typical S:N is 300 in continuum.– Weighted least-squares deconvolution procedure recovers Weighted least-squares deconvolution procedure recovers

profile information from up to 4600 images of 2700 lines. profile information from up to 4600 images of 2700 lines.

• Nice for Stokes I tooNice for Stokes I too– Huge sensitivity gain – turns the AAT into a 160-m Huge sensitivity gain – turns the AAT into a 160-m

telescope!telescope!– Allows use of full time and wavelength resolution.Allows use of full time and wavelength resolution.– Unprecedented amounts of surface detail recoverable.Unprecedented amounts of surface detail recoverable.

* =

Weight =g-factor * depth

Detecting magnetic fieldsDetecting magnetic fields

• Zeeman effect in spectral linesZeeman effect in spectral lines• circular and linear circular and linear • polarisation in line profilespolarisation in line profiles

• amplitude usually < 0.1% amplitude usually < 0.1%

Detecting magnetic fieldsDetecting magnetic fields

• Zeeman effect in spectral linesZeeman effect in spectral lines• circular and linear circular and linear • polarisation in line profilespolarisation in line profiles

• amplitude usually < 0.1%amplitude usually < 0.1%

• Stack line profiles with Stack line profiles with Least-squares Least-squares Deconvolution Deconvolution

•

Stokes V time-series spectraStokes V time-series spectra

Stokes I & V dynamic spectra of AB DorStokes I & V dynamic spectra of AB Dor

• Demonstrates rotational Demonstrates rotational modulation of Zeeman modulation of Zeeman signaturesignature

• Yields location ofYields location of magnetic regions & magnetic regions & orientation of field linesorientation of field lines

Radial field: 1996 Dec 23 - 29Radial field: 1996 Dec 23 - 29

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The shape of a stellar coronaThe shape of a stellar corona• Altshuler & Newkirk Altshuler & Newkirk

(1969):(1969): – fitted potential field models fitted potential field models

to solar surface to solar surface magnetograms.magnetograms.

– Mimic transition from Mimic transition from closed corona to solar wind closed corona to solar wind by imposing a “source by imposing a “source surface” at several solar surface” at several solar radii. Field beyond source radii. Field beyond source surface is radial.surface is radial.

• Can we do this for Can we do this for other stars?other stars?

Coronal topology and X-ray Coronal topology and X-ray emission emission

• Jardine, Wood, Cameron, Jardine, Wood, Cameron, Donati & Mackay(2002) Donati & Mackay(2002) MNRAS, 336:MNRAS, 336:

• Potential field.Potential field.– 1995 Dec 7-11 + 1996 Dec 23-29 1995 Dec 7-11 + 1996 Dec 23-29

magnetograms magnetograms

• AB Dor rotation rate.AB Dor rotation rate.• Isothermal coronaIsothermal corona

– T=10T=1077 K K

• Base pressure Base pressure B B2 2 ..– But p=0 on open linesBut p=0 on open lines

• Soft X-ray emissivity Soft X-ray emissivity n nee2 2 ..

• Monte Carlo RT code .Monte Carlo RT code .• Centrifugal Centrifugal

compression/stripping: compression/stripping: – p=0 on field lines where p > Bp=0 on field lines where p > B2 2 / /

2µ 2µ (cf. Mestel & Spruit 1987)(cf. Mestel & Spruit 1987)

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Centrifugal stripping and Centrifugal stripping and supersaturationsupersaturation

P = 0.51 d P=0.17 dJardine 2004

Centrifugal stripping and Centrifugal stripping and supersaturationsupersaturation

• Co-rotation radius shrinks as Ω increasesCo-rotation radius shrinks as Ω increases

• Loops near co-rotation burst openLoops near co-rotation burst open

• Coronal X-ray emission measure decreases Coronal X-ray emission measure decreases

Jardine 2004

Slingshot prominences: Slingshot prominences: signaturessignatures• AB Dor, AB Dor,

AAT/UCLES, AAT/UCLES, 1996 Dec 291996 Dec 29

• Donati et al 1999Donati et al 1999

Starspotsignatures inphotospheric lines

-v sin i +v sin i

Absorptiontransients inH alpha

-v sin i +v sin i

Coronal condensations: single Coronal condensations: single starsstars

• Detected in 90% of young (pre-) Detected in 90% of young (pre-) main sequence stars with Pmain sequence stars with Protrot<1 <1 dayday

– AB Dor (K0V): AB Dor (K0V): Collier Cameron &Robinson Collier Cameron &Robinson 1989 1989

– HD 197890 =“Speedy Mic” (K0V): HD 197890 =“Speedy Mic” (K0V): Jeffries Jeffries 19931993

– 4 G dwarfs in 4 G dwarfs in Per cluster: Per cluster: Collier Collier Cameron & Woods 1992Cameron & Woods 1992

– HK Aqr = Gl 890 (M1V): HK Aqr = Gl 890 (M1V): Byrne, Eibe & Byrne, Eibe & Rolleston 1996Rolleston 1996

– RE J1816+541: RE J1816+541: Eibe 1998Eibe 1998– PZ Tel: PZ Tel: Barnes et al 2000Barnes et al 2000 (right) (right) PProtrot = 1 = 1

day (slowest yet)day (slowest yet)– Pre-main sequence G star RX J1508.6-Pre-main sequence G star RX J1508.6-

4423 4423 (Donati et al 2000) (Donati et al 2000) --prominences in --prominences in emission!emission!

Emission signaturesEmission signatures• Seen only in the most rapidly-rotating, early G Seen only in the most rapidly-rotating, early G

dwarfs, e.g. RX J1508.6 -4423 (Donati et al dwarfs, e.g. RX J1508.6 -4423 (Donati et al 2000):2000):

Star is viewed at low inclination; uneclipsed H-emitting clouds trace out sinusoids

Tomographic back-projectionTomographic back-projection• Clouds congregate near co-rotation radius Clouds congregate near co-rotation radius

(dotted).(dotted).• Little evidence of material inside co-rotation Little evidence of material inside co-rotation

radius.radius.• Substantial evolution of gas distribution over 4 Substantial evolution of gas distribution over 4

nights.nights.

Latitude dependenceLatitude dependence• AB Dor prominences need to be anchored at AB Dor prominences need to be anchored at

high latitude to cross stellar disk, since i = 60 high latitude to cross stellar disk, since i = 60 degrees.degrees.

• What about other stars with different What about other stars with different inclinations?inclinations?

– BD+22 4409: Low inclination, no transients found: BD+22 4409: Low inclination, no transients found: Jeffries Jeffries et al 1994et al 1994

Where do bipoles emerge on Where do bipoles emerge on young stars?young stars?

• Solar-type starSolar-type star• Bipoles emerge at solar-like Bipoles emerge at solar-like

latitudes as cycle progresses.latitudes as cycle progresses.• Solar transport coeffs.Solar transport coeffs.• Flux emergence rate 30 times Flux emergence rate 30 times

solar.solar.• Solar meridional flow rate (11 Solar meridional flow rate (11

m/sec)m/sec)• 2 cycles per movie loop.2 cycles per movie loop.• Van Ballegooijen code, Van Ballegooijen code,

modified by Duncan Mackay.modified by Duncan Mackay.• Confirms earlier work by Confirms earlier work by

Schrijver & Title for similar flux Schrijver & Title for similar flux emergence rate.emergence rate.

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• Solar-type starSolar-type star• Bipoles emerge at latitudes 70 Bipoles emerge at latitudes 70

deg to 10 deg as cycle deg to 10 deg as cycle progresses.progresses.

• Solar transport coeffs.Solar transport coeffs.• Flux emergence rate 30 times Flux emergence rate 30 times

solar.solar.• Solar meridional flow rate (11 Solar meridional flow rate (11

m/sec)m/sec)• 2 cycles per movie loop.2 cycles per movie loop.• Flux vanishes at all latitudes Flux vanishes at all latitudes

around activity minimum.around activity minimum.• Mostly unipolar caps.Mostly unipolar caps.




• Solar-type starSolar-type star• Bipoles emerge at latitudes 70 Bipoles emerge at latitudes 70

deg to 10 deg as cycle deg to 10 deg as cycle progresses.progresses.


solar.solar.• 9 x Solar meridional flow rate 9 x Solar meridional flow rate

(100 m/sec)(100 m/sec)• 2 cycles per movie loop.2 cycles per movie loop.• Flux vanishes at all latitudes Flux vanishes at all latitudes

around activity minimum.around activity minimum.• Multipolar caps.Multipolar caps.




• Solar-type starSolar-type star• Bipoles emerge at range of Bipoles emerge at range of

latitudes around 35 degrees latitudes around 35 degrees (no butterfly diagram).(no butterfly diagram).



(100 m/sec)(100 m/sec)• 2 cycles per movie loop.2 cycles per movie loop.• Flux vanishes at all latitudes Flux vanishes at all latitudes





• Solar-type starSolar-type star• Bipoles emerge at range of Bipoles emerge at range of

latitudes around 35 degrees latitudes around 35 degrees (no butterfly diagram).(no butterfly diagram).



(100 m/sec)(100 m/sec)• Slow-motion action replay.Slow-motion action replay.• Flux vanishes at all latitudes Flux vanishes at all latitudes


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Slingshot prominences and polar Slingshot prominences and polar fieldsfields

• McIvor et al 2003McIvor et al 2003• Possible polar field Possible polar field

configurations:configurations:



Slingshot prominences and polar Slingshot prominences and polar fieldsfields

• McIvor et al 2003McIvor et al 2003• Corresponding Corresponding

coronal field coronal field configurations:configurations:

• Unipolar cap Unipolar cap supports fewer supports fewer high-latitude high-latitude prominences.prominences.



Summary and prospects Summary and prospects • Rotational shear ∆ΩRotational shear ∆Ω

– Decreases strongly with increasing convective-zone depthDecreases strongly with increasing convective-zone depth– Increases weakly with increasing stellar rotation rate.Increases weakly with increasing stellar rotation rate.

• Differential rotation rate shows year-to-year variability Differential rotation rate shows year-to-year variability – Consistent with Applegate (1992) mechanism for binaries.Consistent with Applegate (1992) mechanism for binaries.

• Polar spot activity appears stronger in shallow Polar spot activity appears stronger in shallow convective zones.convective zones.

• Advection and diffusion of emergent bipoles can give rise Advection and diffusion of emergent bipoles can give rise to flux pile-up at polar caps.to flux pile-up at polar caps.

• Prominence distribution suggests mixed-polarity caps.Prominence distribution suggests mixed-polarity caps.• Enhanced poleward meridional flows may be needed.Enhanced poleward meridional flows may be needed.

– Should be detectable if present.Should be detectable if present.

magnetic activity on rapidly rotating stars i: surface flux distributions

Documents

spot temperature

rotation f

spot lifetimemap

dense spot coveragetio

magnetic polarity distribution

band ratio

noyes et

krster et