1. Short Introduction1. Short Introduction

1.1 Overview of helioseismology 1.1 Overview of helioseismology results and prospectsresults and prospects

Helioseismology: Helioseismology: A tool to help answer fundamental questionsA tool to help answer fundamental questions

What is the mechanism of the solar cycle?What is the mechanism of the solar cycle? Dynamo theory: motions generate magnetic Dynamo theory: motions generate magnetic

fieldfield Large-scale flows, convective flowsLarge-scale flows, convective flows Internal magnetic fieldInternal magnetic field Active regions: structure, emergence, Active regions: structure, emergence,

evolutionevolution Drivers of space weather Drivers of space weather Basic physics: neutrinos, G, etc.Basic physics: neutrinos, G, etc.

The eleven-year solar cycle

Solar oscillationsSolar oscillations

•The Sun is filled with acoustic waves, with periods near 5 min.

•Waves are excited by near-surface turbulent convection

•Surface motions are a few 100 m/s, superimposed on the 2 km/s solar rotation.

Solar tsunami (flare induced)

Global helioseismology

•Measurement and inversion of the frequencies of the global modes of resonance (millions of modes).

•Among the most precise measurements in astrophysics: some frequencies are known with a precision of 1 ppm.

•Sound speed difference from best solar model.•Maximum deviation is 2% (red is faster, blue is slower than model).•Small surface variations on 11-yr time scale.

Solar structure

Internal rotation

•Differential rotation in the convective envelope.•Uniform rotation in the radiative interior.•Near-surface shear layer.

red is faster (26 days) blue is slower (35 days).

The pulse of the solar dynamo?The pulse of the solar dynamo?

Local helioseismologyLocal helioseismology

• Measure travel times of wavepackets travelling between any two points A and B on the solar surface.

• Differences between the A→B and B→A directions arise from bulk motion along the path.

• 3-D maps of flows and temperature beneath the surface.

Rotation Variations

Meridional Circulation

Far-side Imaging Solar Subsurface Weather

Magnetic Connectivity

Subsurface flows

Interior Structure

Convection

Solar subsurface ‘weather’Solar subsurface ‘weather’

Red regions have higher wave speed, blue slower.

Sunspot internal structure

Supergranulation and Supergranulation and network evolutionnetwork evolution

Map of Sun’s large magnetic regions

0 180 360

90N

90S

Sun rotates in 27 days so images willmove to left since map grid is fixed

Far-side imaging

Current topics of researchCurrent topics of research

Detect magnetic field in the solar Detect magnetic field in the solar interior, i.e. decouple magnetic from interior, i.e. decouple magnetic from other types of perturbationsother types of perturbations

Emergence and evolution of active Emergence and evolution of active regions from limb to limbregions from limb to limb

Probe deeper layers in the Probe deeper layers in the convection zoneconvection zone

Missions aheadMissions ahead

Solar Dynamics Observatory (LWS NASA)

Launch Date: April 2008

Mission Duration: 5 years, 10 yr of expendables

Orbit: 36000 km, circular, 28.5º geo. synch. Inclined

1’’ resolution, full disk, high duty cycle.

Ideal for local helioseismology.

Solar Orbiter (ESA)

Launch Date: 2015

Mission Duration: 5 (nominal) to 7 years (ext.)

Orbit: Assisted by Venus swing-bys, the spacecraft's 150-day orbit will evolve gradually over the mission lifetime from an inclination of about 12 to 35 degrees to the solar equator.

Stereoscopic observations:Stereoscopic observations:Solar Orbiter, Sentinel, Safari (?)Solar Orbiter, Sentinel, Safari (?)

AsteroseismologyAsteroseismology

Mass, radius, chemical composition, Mass, radius, chemical composition, and age of isolated stars and age of isolated stars

Independent test of theory of stellar Independent test of theory of stellar structure and evolutionstructure and evolution

Internal stellar rotationInternal stellar rotation Constraints on dynamo theoriesConstraints on dynamo theories ConvectionConvection Implications for planetary system Implications for planetary system

formationformation

All stars are suspected to pulsateAll stars are suspected to pulsate

Solar-like oscillationsSolar-like oscillations

Cen A

Sun

Asteroseismology projectsAsteroseismology projects

GroundGround MOST (Canada)MOST (Canada) COROT (ESA, COROT (ESA,

2006)2006) Kepler (NASA, Kepler (NASA,

2006)2006) Eddington? (ESA)Eddington? (ESA) Stellar Imager? Stellar Imager?

Points to keep in mindPoints to keep in mind

Helioseismology is the only way to solve the Helioseismology is the only way to solve the long-standing puzzle of solar cycle.long-standing puzzle of solar cycle.

In particular, techniques of local In particular, techniques of local helioseismology in combination with high-helioseismology in combination with high-resolution space data will be key in revealing resolution space data will be key in revealing the interactions between flows and magnetic the interactions between flows and magnetic fields in the interior.fields in the interior.

Asteroseismology will be an extremely Asteroseismology will be an extremely valuable tool to study stellar activity and valuable tool to study stellar activity and evolution.evolution.

Asteroseismology is on the eve of a revolution Asteroseismology is on the eve of a revolution with the launch of COROT (Dec 2006).with the launch of COROT (Dec 2006).

Average “magnetic tube”Average “magnetic tube”

Radial distance (Mm)

Fie

ld s

tren

gth

(G)

Average of 45 magnetic features over 4 hrTracked MDI hires magnetogram (average of abs value over 4 hr)

250 Mm

FWHM ~ 1Mm

Scattering f modes by kink modeScattering f modes by kink mode(Bogdan’s solution)(Bogdan’s solution)

All stars are suspected to pulsateAll stars are suspected to pulsate

-2

0

2

4

6

5.0 4.5 4.0 3.5

log Tefflog Teff

log

(L

/L)

log

(L

/L)

Main Sequence

Solar-type stars

Mira LPVs

Cepheids

Irregular LPVs

DBVs

DDVs

PNNVs

Instability Strip

Classical Cepheids

RR Lyrae Scutis

VW Virginis

ZZ Ceti (DAVs)

Different mechanisms invoked

Collar flows probably hold the spot together.

Sunspot internal dynamics