Stellar Evolution: After the Main Sequence
Guiding Questions
A star’s lifetime on the main sequence is proportional to its mass divided by its luminosity
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When core hydrogen fusion ceases, a main-sequence star becomes a red giant
Red Giants
As stars age and become giant stars, they expand tremendously and shed matter into space
Fusion of helium into carbon and oxygen begins at the center of a red giant
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After the helium flash, a low-mass star moves quickly from the red-giant region of the H-R diagram to the horizontal branch
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The cluster’s age is equal to the age of the main-sequence stars at the turnoff point (the upper end of the remaining main sequence)
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As a cluster ages, the main sequence is “eaten away” from the upper left as stars of progressively smaller mass evolve into red giants
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Stellar evolution has produced two distinct populations of stars
Many mature stars pulsate
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There is a direct relationship between Cepheid periods of pulsation and their luminosities
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Mass transfer can affect the evolution of close binary star systems
Gas flowing from one star to the other passes across the inner Lagrangian point
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This mass transfer can affect the evolutionary history of the stars that make up the binary system
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Key Words
Author: Michael Cohen
E-mail: mrcohe@ship.edu
Homepage: http://physics.ship.edu/~mrc/