Chapter 12

Chapter 12 - Note that the following lectures include...

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Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode).
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Stellar Evolution Chapter 12
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This chapter is the heart of any discussion of astronomy. Previous chapters showed how astronomers make observations with telescopes and how they analyze their observations to find the luminosity, diameter, and mass of stars. All of that aims at understanding what stars are. This is the middle of three chapters that tell the story of stars. The preceding chapter told us how stars form, and the next chapter tells us how stars die. This chapter is the heart of the story—how stars live. As always, we accept nothing at face value. We expect theory to be supported by evidence. We expect carefully constructed models to help us understand the structure inside stars. In short, we exercise our critical faculties Guidepost
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and analyze the story of stellar evolution rather than merely accepting it. After this chapter, we will know how stars work, and we will be ready to study the rest of the universe, from galaxies that contain billions of stars to the planets that form around individual stars. Guidepost (continued)
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I. Main-Sequence Stars A. Stellar Models B. Why There Is a Main Sequence C. The Ends of the Main Sequence D. The Life of a Main-Sequence Star E. The Life Expectancies of Stars II. Post-Main-Sequence Evolution A. Expansion into a Giant B. Degenerate Matter C. Helium Fusion D. Fusing Elements Heavier than Helium Outline
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III. Evidence of Evolution: Star Clusters A. Observing Star Clusters B. The Evolution of Star Clusters IV. Evidence of Evolution: Variable Stars A. Cepheid and RR Lyrae Variable Stars B. Pulsating Stars C. Period Changes in Variable Stars Outline (continued)
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The structure and evolution of a star is determined by the laws of Main Sequence Stars Hydrostatic equilibrium Energy transport Conservation of mass Conservation of energy A star’s mass (and chemical composition) completely determines its properties. That’s why stars initially all line up along the main sequence.
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Maximum Masses of Main-Sequence Stars η Carinae (Eta Carinae) M max a) More massive clouds fragment into smaller pieces during star formation. b) Very massive stars lose mass in strong stellar winds Example: η Carinae: Binary system of a 60 M sun and 70 M sun star. Dramatic mass loss; major eruption in 1843 created double lobes. ~ 100 solar masses
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Minimum Mass of Main-Sequence Stars M min = 0.08 M sun At masses below 0.08 M sun , stellar progenitors do not get hot enough to ignite thermonuclear fusion. Brown Dwarfs Gliese 229B
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Hard to find because they are very faint and cool; emit mostly in the infrared. Many have been detected in
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Chapter 12 - Note that the following lectures include...

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