1. Overview of the structure of starsStill, First the Sun as an exampleCoronaT=2.000.000KNorthPoleChromospherePholosphere(visible surface)T=5700KCenlerT=15,000,000KEnergyflowHydrogen-burning coreProminencesHydrogen andheliumgas;nonuclearreaclionsConvectivezoneEarthatsame scale
1. Overview of the structure of stars Still, First the Sun as an example
Overview of basic processesNuclear energy production → energy transport(radiation, convection) ;for a system in a long-time equilibrium, massconservation, energy conservation, force balance.Mathematicallytheconditionsforthe internalequilibriumof astar can beexpressed asfour differential equationsgoverningthedistributionofmass,gaspressureandenergyproductionandtransportinthestarPlus theEquationof State(Physical Stateof theGas)andBoundaryConditions.Theseeguationswillbederivedsoon
Overview of basic processes Nuclear energy production → energy transport (radiation, convection) ; for a system in a long-time equilibrium, mass conservation, energy conservation, force balance. Mathematically the conditions for the internal equilibrium of a star can be expressed as four differential equations governing the distribution of mass, gas pressure and energy production and transport in the star. Plus the Equation of State (Physical State of the Gas) and Boundary Conditions. These equations will be derived soon
Connections with observations(Migl-T.2),% Stars:Basic Obsevations 17CoYona升国仍不有Cthinei发付伴SimTminwfokSokm3e0-k(thi）光时限吸伴ttSattony SuhueEnergytransportl:radiationFigure 2.4 A photon insidea star is scattered manytimes until it reaches a radiusfrom which it can escape.The last scattering surfacedefines thebaseof thephotosphere of the star
Connections with observations Maoz, fig2.4 Energy transport I: radiation
Energy transport Il:convection, sound waves and helioseismologyThesolar convection is visible onthe surfaceas thegranulation. At the bright (high-T) center of eachgranule,gas is rising upward, and atthe darker (lowerT) granule boundaries, it is sinking down again. Thesize ofagranuleseenfromthe Earth is typically1"correspondingtoabout10o0 kmonthesolar surfaceThere is also alarger scaleconvection calledsupergranulation inthephotosphere.Thecellsofthesupergranulationmaybe about1'indiameter
Energy transport II: convection, sound waves and helioseismology The solar convection is visible on the surface as the granulation. At the bright (high-T) center of each granule, gas is rising upward, and at the darker (lowerT) granule boundaries, it is sinking down again. The size of a granule seen from the Earth is typically 1”, corresponding to about 1000 km on the solar surface. There is also a larger scale convection called supergranulation in the photosphere. The cells of the supergranulation may be about 1’ in diameter
TheoscillationsweseeonthesurfaceareduetosoundwavesgeneratedandtrappedinsidethesunSoundwaves areproduced bypressurefluctuationsintheturbulentconvectivemotionsofthesun'sinterior.Sincesoundisproducedbypressure,thesemodesofvibrationarecalledp-modes.HelioseismologyThesesoundwaves,andthemodes of vibrationtheyproduce,canbeusedtoprobetheinteriorofthesunthesame waythatgeologists uses seismic wavesfromearthquakestoprobetheinside of the earth. Some of thesewaves travel right throughthecenterofthe sun.Others are bentbacktowardthesurfaceatshallowdepths.Helioseismologistscanusetheproperties of thesewaves todeterminethetemperature,densitycomposition,andmotionoftheinterior of the sun
The oscillations we see on the surface are due to sound waves generated and trapped inside the sun. Sound waves are produced by pressure fluctuations in the turbulent convective motions of the sun's interior. Since sound is produced by pressure, these modes of vibration are called p-modes. Helioseismology These sound waves, and the modes of vibration they produce, can be used to probe the interior of the sun the same way that geologists uses seismic waves from earthquakes to probe the inside of the earth. Some of these waves travel right through the center of the sun. Others are bent back toward the surface at shallow depths. Helioseismologists can use the properties of these waves to determine the temperature, density, composition, and motion of the interior of the sun