UofA/NSO Summer SchoolIntroduction to the Sun 6/17/06 Welcome to the The First Joint Arizona/NSO...

UofA/NSO Summer School Introduction to the Sun6/17/06

Welcome to the The First Joint Arizona/NSO Summer SchoolJune 11-16, NSO Sac Peak Observatory, NM


List of Topics and Lecturers• Helioseismology

– Rachel Howe, NSO, Tucson– Rudi Komm, NSO, Tucson

• Solar Interior– Gordon Petrie, NSO, Tucson

• Radiative Transfer– Han Uitenbroek, NSO, Sac Peak

• Solar Magnetohydrodynamics– Randy Jokipii, UofA, Tucson

• Photospheric and Chromospheric Magnetic Fields– K.S. Balasubramanian (Bala), NSO, Sac Peak

• Solar-Energetic Particles– Joe Giacalone, UofA, Tucson

• Space Weather– Tom Bogan, NCAR, Boulder


List of Activities

• Computer software programs– RASL/DASL CDs and workbooks– xsolar (Chris Russell, UCLA)

• Solar wind, interplanetary magnetic fields

– Helioseismology application widget (Rachel Howe)

• Solar viewing through Hα telescopes– Outside of visitor center

• Poster viewing/discussion


List of Other Activities

• Monday – reception at the director’s house• Tuesday – White Sands picnic• Wednesday –

– Tour of NSO facilities, – Community BBQ

• Thursday – Pizza Night / Star Party


The Physics of the Sun


Why Study the Sun ?

• Influence on Earth

• Important for Astronomy– Only star that we can see closely

• The source of many interesting and important physics problems

• For Me?– Many basic properties are a mystery!

• dynamo, coronal heating, source of high-energy particles, etc.

– Space radiation environment, space weather, acceleration of high-energy charged particles


Source of the Sun’s Internal Energy:p-p chain is dominate for the Sun; also CNO chain


Solar Structure: The Standard Solar

Model

• Theoretical model used to determine the physical properties of the Sun’s interior

• Hydrostatic and thermal equilibrium– A big ball of gas held together by

gravity + radiative diffusion

• Can add convection, but this is difficult (simple approach – mixing-length theory)

• Nuclear reaction rates and opacities are needed

• Boundary conditions are tricky – need to use an iterative approach


Solar Oscillations

• Waves can propagate through the Sun causing a variety of vibrations– Like sound waves

• These are used to infer pressures, densities, chemical compositions, and rotation rates within the Sun – Constraints on solar

models

• Helioseismology


• Turbulent convective motions cause overturning (bubbling) motions inside the Sun. – These are responsible for

the granulation pattern seen on the Sun’s surface.

– Rayleigh-Bénard convection


Recent High-resolution Images of

granulation


The photosphere

• About 5700K– Coolest region of the

Sun (coldest in sunspots)

• Sunspots (usually in pairs)

• Variety of convection cells (granulation, supergranulation, etc.)

• Limb Darkening


The Chromosphere

• Above the photosphere is a layer of less dense but higher temperature gases called the chromosphere

“Color Sphere”

• characterized by spikesof rising gas

• Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules


The Corona

• The outermost layer of the solar atmosphere, the corona, is made of very high-temperature gases at extremely low density

• The solar corona blends into the solar wind at great distances from the Sun

• Because the corona is very hot, it is best viewed in the x-ray part of the spectrum

• What heats the corona remains an open question!


Emission Spectra in the UV

Far UV

To the far rightof this plot is theextreme UV (soft X-ray)

Near UV

Dupree et al., ApJ, 1973


SOHO/EIT image at 195 Angstroms (FeXII)


Sunspots

• Existence known since 350 BC (Greece), 28 BC (China)

• Lower temperature

• Umbra and penumbra

• Associated with Intense magnetic fields– Zeeman effect


The Babcock model andSolar Dynamo


The 11-year Sunspot Cycle

Number of Sunspots versus time – they come and go every 11 years

Number of Sunspots versus latitude – forms a “butterfly pattern”


The Sun and Earth’s Climate:The Maunder Minimum

• Complete absence of sunspots for 50 years corresponds to a mini ice age

• There is a loose correlation between global man temperature and sunspots


Magnetism is the Key to Understanding the Sun


Coronal loops expand from the surface of the Sun following a solar explosion (solar flare) on April 21, 2002

TRACE movie


The Buildup and release of magnetic field energy

• CMEs and Flares– A solar flare is a brief

eruption of hot, ionized gases from a sunspot group

– A coronal mass ejection (CME) is much larger

• Geomagnetic storms

• High-Energy Particles (Space Radiation)

Halloween 2003 storms


The Sun is the Most Important Particle Accelerator in the Solar System


Aurora in Tucson


SOHO/LASCO (C3) Coronagraph

“Halloween” solar storms of 2003


Propagating Shocks

• Analogy with sonic booms

• Efficient particle accelerators

• Radiation Environment and Space Weather


My research has shown that the angle between the shock propagation direction and the magnetic field determines the maximum energy in the particle events

Perpendicular shocks high-energy particles


Perpendicular Shocks in the solar atmosphere


Analogy to Cosmic Rays and Supernove remants:Supernova Remnant 1006 – Chandra image


To Finish

UofA/NSO Summer SchoolIntroduction to the Sun 6/17/06 Welcome to the The First Joint Arizona/NSO...

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