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lect 14 - Question 6-1 HR diagram for two open clusters...

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HR diagram for two open clusters. Based on the diagram, which statement is true? A. M 67 is older than NGC 188 B. M 67 is younger than NGC 188 C. Both are the exactly same age. D. There is not enough information to determine the age of the clusters. Question 6-1
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Cepheid variable stars are very luminous and can be observed over very large distances. Why are such stars important to astronomers ? A. They confirm the theory of nuclear fusion as the energy source for stars. B. They can be used as distance indicators because their luminosity can be determined from their period. C. Such stars are unstable and are about to become supernovae. D. Their age can be determined directly from their period. E. They are always found in binary systems. Question 6-2
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Horizontal-branch stars are stars that have left the main sequence. Inside such stars A. no fusion is occurring in the core, and hydrogen fusion is occurring in a shell around the core. B. both core helium fusion and shell hydrogen fusion are taking place. C. helium fusion is occurring in the core, and there is no hydrogen fusion. D. both core hydrogen fusion and shell helium fusion are taking place. Question 6-3
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A helium flash occurs A because helium is explosive and cannot be controlled when nuclear reactions occur. B because degenerate electrons in the core do not allow the core to expand as it heats up. C in Cepheid variables. D in stars with masses less than 0.4 Solar Mass. E None of the above is true about a helium flash. Question 6-4
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What physical characteristic most determines the main sequence lifetime of a star? A radius B composition C mass D luminosity class E none of the above Question 6-5
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When the solar core has mostly been transformed from hydrogen into helium, the Sun will move to the next phase of its life cycle, changing gradually into a A different type of main sequence star B planet C protostar D red giant E white dwarf Question 6-6
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Diagram of the evolution for a one- solar mass star. Select the correct combination of answers: A There is no Hydrogen fusion during stage 2 B At point 3, the Helium flash occurs. C During stage 4, C and O fusion occurs in the core. D During stage 5, the star becomes a red giant for a 2 nd time (AGB). E Point 6 corresponds to the planetary nebula stage. F the star explodes as a supernova in stage 7. Question 6-7
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A planetary nebula can best be defined as A a flat disk of material around a protostar.
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