Stellar Structure Gas Mass Radiation Energy Generation Transport Radiative Convective Temperature Density Composition Hydrostatic Equilibrium:

Hydrostatic Equilibrium A FpFp mm rr FgFg F’ p

The Pressure Integral A AA xx v p   cos 

Overcoming the Coulomb Barrier U cl = (3/2) kT cl → kT cl ~ K U t = (3/2) kT t → kT cl ~ 10 7 K r t ~ deBrogle = h/p

The PP Chain

The CNO Cycle 12 6 C p  13 7 N e e+e Cp  14 7 N p  15 8 O e e+e N p 4 2 He

Binding energy per nucleon Exothermic Endothermic Energy can be liberated via nuclear fusion Energy can be liberated via nuclear fission

Convection Adiabatic expansion: P = K*  

Favorable Conditions for Convection Large Opacities → Large |dT/dr| rad Partial Ionization Zones → Brings  close to 1 → small |dT/dr| ad Low g → small |dT/dr| ad = g/C p Strongly T-dependent energy generation (CNO cycle!) → large |dT/dr|

Stellar energy transport structure as a function of stellar mass Low-mass stars (M < 0.25 M 0 ): Completely convective Sun-like stars (0.25 M 0 < M < 1.2 M 0 ): Radiative core; convective envelope High-Mass stars (M > 1.3 M 0 ): Convective core; radiative envelope M/M 0 R/R *

Vogt-Russell Theorem The mass and composition of a star uniquely determine its radius and luminosity, internal structure, and subsequent evolution. => Almost 1-dimensional Zero-Age Main Sequence (ZAMS)

Masses of Stars in the Hertzsprung- Russell Diagram Masses in units of solar masses Low masses High masses Mass The higher a star’s mass, the more luminous (brighter) it is: High-mass stars have much shorter lives than low-mass stars: Sun: ~ 10 billion yr. 10 M sun : ~ 30 million yr. 0.1 M sun : ~ 3 trillion yr. L ~ M 3.5 t life ~ M -2.5

Mass Sun Radiative Core, convective envelope; Energy generation through PP Cycle Convective Core, radiative envelope; Energy generation through CNO Cycle Summary: Stellar Structure

Energy Transport Structure Inner radiative, outer convective zone Inner convective, outer radiative zone CNO cycle dominantPP chain dominant