Astrophysics 2: Stellar and Circumstellar Physics

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Astrophysics 2Stellar and Circumstellar Physics
2. Stellar Structure
http//www.arc.hokkai-s-u.ac.jp/
okazaki/astrophys-2/
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2.1. Basic equations for stellar structure
Basic equations
Eq. of continuity Eq. of motion Eq. of energy
transport Eq. of energy Eq. of state Eq. for
chemical composition
bcs at the center and the surface
stellar structure
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mass inside of the sphere with radius
luminosity at radius
density
pressure
temperature
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Equation of continuity
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Equation of motion
acceleration
Pressure gradient force
gravity
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Temperature gradient
Radiative equilibrium
with
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Convective equilibrium
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Energy equation
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2.2. Timescales
2.2.1. Free-fall time
(ex collapse of a molecular cloud core)
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2.2.2. Kelvin-Helmholtz timescale
Gravitational energy
Luminosity
(ex Contraction of a protostar)
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2.2.3. Nuclear timescale
mass fraction available for nuclear reactions
mass abundance
energy generation per unit mass
(ex main-sequence stars)
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2.3. Virial Theorem
Eq. of motion
Internal energy
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virial theorem
In order for a star to be gravitationally bound,
Gravitationally bound systems have negative
specific heats.
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2.4. Convection
Schwarzshild criterion for dynamical stability
If
, the layer becomes
dynamically unstable and convection begins.
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2.5. Nuclear reactions in stars
2.5.1. Proton-proton chain reaction
PPI
http//en.wikipedia.org/wiki/Proton-proton_chain_r
eaction
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pp-chain reaction
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2.5.2. CNO cycle
http//en.wikipedia.org/wiki/CNO_cycle
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2.5.2. CNO cycle
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CNO cycle
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pp-chain reaction vs. CNO cycle
Stars with
pp-chain is the dominant reaction.
Core is in radiative equilibrium.
Stars with
CNO cycle is dominant.
Core is in convective equilibrium.
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pp-chain reaction vs. CNO cycle
http//csep10.phys.utk.edu/astr162/lect/energy/cno
-pp.html
Energy production rate is very sensitive to
temperature in CNO cycle.