Ch20 - Assignment: Chapter 20 Class: Astronomy I Date:...

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Assignment: Chapter 20 Class: Astronomy I Date: November 7 th , 2007 Review Questions 1. The luminosity changes relatively little during this stage, so the evolutionary track moves almost horizontally, along a path called the horizontal branch. Horizontal- branch stars have helium-fusing cores surrounded by hydrogen-fusing shells. 2. Horizontal-branch stars are basically main-sequence stars only with helium rather than hydrogen. 3. AGB stars approach the red-giant branch from the left on an H-R diagram. 4. The third dredge-up transports large amounts of freshly synthesized carbon to the star’s surface, and the star’s spectrum thus exhibits prominent absorption bands of carbon-rich molecules. 5. Some 4.56 billion years ago a clump of the interstellar medium which contained this carbon coalesced into the solar nebula from which our Earth eventually formed. 6. When a helium shell flash occurs, the luminosity of AGB star increases substantially in a relatively short-lived burst called a thermal pulse. 7. A dying star’s hot core become exposed and emits ultraviolet radiation intense enough to ionize and excite the expanding shell of ejected gases. These gases glow and emit visible light through the process of fluorescence, producing a planetary nebula. 8.
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Ch20 - Assignment: Chapter 20 Class: Astronomy I Date:...

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