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Star Lifetimes and Chemical Composition (Red Giants (Red Giant Branch…
Star Lifetimes and Chemical Composition
Horizontal Branch Stars
Generation of Energy
CNO Cycle
in a shell surrounding the core.
Triple-alpha process
in the core.
Key Features
Immediately follows the red giant branch in stars whose masses are similar to the Sun's.
Reduced luminosity, contracted stellar envelope, and higher surface temperatures.
Main Sequence Stars
Generation of Energy
CNO Cycle
in "upper main sequence" stars.
Proton-proton chain
in "lower main-sequence" stars.
Life Cycle
Lifespan can be approximated with equations sheet.
Red Giants
Red Giant Branch
Generation of Energy
Inert helium core.
Fuse hydrogen around the core.
Asymptotic Giant Branch
Generation of Energy
Degenerate carbon-oxygen core.
Helium burning shell outside of the core.
Hydrogen burning shell outside of the helium shell.
Horizontal Branch (Cool Half)
Generation of Energy
Triple-alpha process
.
Protostars
Life Cycle
4 Main Classes
I: Peak Emission is far-infrared. Star lasts 10^5 years.
II: Peak Emission is near-infrared. Star lasts 10^6 years.
0: Peak Emission is sub-millimeter. Star lasts 10^4 years.
III: Peak Emission is visible. Star lasts 10^7 years.
Protostars from "dense cores" which are small molecular clouds. They evolve when they blow back infalling gas as the molecular collapses.
Generation of Energy
Radiation liberated at pressure shocks on its surface and on the surface of the surrounding disk. The dust around the star absorbs photons and re-radiates them at longer wavelengths which means they cannot be detected optically.
Gas and Magnetic pressure balance gravity.
These stars fuse deuterium.
Composition
71.1% Hydrogen
27.4% Helium
1.5% Metals