1. short introduction 1.1 overview of helioseismology results and prospects
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1. Short Introduction 1.1 Overview of helioseismology results and prospects. Helioseismology: A tool to help answer fundamental questions. What is the mechanism of the solar cycle? Dynamo theory: motions generate magnetic field Large-scale flows, convective flows Internal magnetic field - PowerPoint PPT PresentationTRANSCRIPT
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