Seminar assignments - Quiz 5 PDF

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quiz 5...

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Section 1 1. A star is on the horizontal branch of the H-R diagram. Which statement is true?



It is burning carbon.



It is burning helium. (Correct)



The star is about to return to the main sequence.



The star is contracting.



It is about to experience the helium flash.

2. Which of these would typically be the brightest star in a young open cluster?



G2V



K3II



M3Ia



B1V (Correct)



A2Ib

3. The outward pressure in the core of a red giant balances the inward pull of gravity when



carbon fuses into heavier elements.



iron forms in the inner core.



hydrogen begins fusing into helium. (Incorrect)



the electrons and protons have combined to form neutrons.



the electron orbits are compressed so much they are all in contact.

4. A cloud fragment too small to collapse into a main sequence star becomes a



planet of another star.



T-Tauri object.



brown dwarf. (Correct)



pulsar.



white dwarf.

5. A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?



nova (Correct)



gamma ray burstar



Type I supernova



hypernova



Type II supernova

6. As a star's evolution approaches the Type II supernova, we find



helium to carbon fusion takes at least 100 million K to start.



the heavier the element, the less time it takes to make it.



the heavier the element, the higher the temperature to fuse it.



photo disintegration of iron nuclei begins at 10 billion K to ignite the supernova.



All of the above are correct. (Correct)

7. A star (no matter what its mass) spends most of its life



as a main-sequence star. (Correct)



as a T-Tauri variable star.



as a protostar.



as a planetary nebula.



as a red giant or supergiant.

8. As a 6 solar-mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity



increases.



first increases, then decreases.



decreases.



remains roughly constant. (Correct)



first decreases, then increases.

9. What temperature is needed to fuse helium into carbon?



15 million K



5,800 K



one billion K



100,000 K



100 million K (Correct)

10. Stars evolve along the main sequence.



True (Incorrect)



False

11. Approximately how many brown dwarfs are believed to exist in the Milky Way galaxy?



one million



ten trillion



one hundred billion (Correct)



100,000



one billion

12. Can a star become a red giant more than once?



yes, before and after the Type II supernova event



yes, before and after the helium flash



no, it will lose so much mass as to cross the Chandrasekhar Limit (Incorrect)



no, the planetary nebula blows off all the outer shells completely



no, or we would see them as the majority of naked-eye stars

13. A star cluster with a lot of hot, blue stars must be relatively young.



True (Correct)



False

14. During the T-Tauri phase of a protostar, it



changes its spin direction.



may develop very strong winds. (Correct)



expands dramatically.



begins a period of reduced activity.



lies on the main sequence.

15. A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of 4 million K will become a



T-Tauri star.



brown dwarf. (Correct)



stage 1 protostar.



black hole.



black dwarf

16. The helium flash converts helium nuclei into



boron.



iron.



beryllium.



oxygen.



carbon. (Correct)

17. On an H-R diagram, a protostar would be



above and to the right of the main sequence. (Correct)



on the main sequence at the extreme lower right.



above and near the upper left of the main sequence.



below and near the right side of the main sequence.



below and to the left of the main sequence.

18. At what core temperature does hydrogen begin to fuse to helium?



10 million K



1 million K



100 million K (Incorrect)



3,000 K



5,800 K

19. When a low mass star first runs short of hydrogen in its core, it becomes brighter because



the core contracts, raising the temperature and extending the hydrogen burning shell outward.



its outer, cooler layers are shed, and we see the brighter central core.



the helium flash increases the size of the star immensely. (Incorrect)



helium fusion gives off more energy than does hydrogen.



it explodes as a nova.

20. How long does it take an M-type star to reach the main sequence, compared to a solar-type star?



about twice as long



a tenth as long



longer than the age of the Galaxy



about the same, 30 million years



about twenty times longer (Correct)

21. Which of these evolutionary paths is the fate of our Sun?



brown dwarf



nova



pulsar



planetary nebula (Correct)



supernova of Type II

22. Which of these would typically be among the brightest stars in an ancient globular cluster?



A4



B3



M5



O3



K3 (Correct)

23. Why are star clusters ideal "laboratories" for stellar evolution?



Their stars are all about the same age, composition, and distance from us. (Correct)



Their stars are all about the same mass and temperature.



The combined light of all the stars makes them easier to see.



Their stars are all the same composition and stage in evolution.



Like our Sun, they lie in the plane of the Milky Way.

24. A solar-mass star will evolve off the main sequence when



it expels a planetary nebula to cool off and release radiation.



it builds up a core of inert helium. (Correct)



it completely runs out of hydrogen.



it explodes as a violent nova.



it loses all its neutrinos, so fusion must cease.

25. Which of these is true of planetary nebulae?



They are expelled by the most massive stars in their final stages before supernova.



They are rings of material around protostars that will accrete into planets in time.



They are the material which causes the eclipses in eclipsing binary systems.



They are ejected envelopes surrounding a highly evolved low-mass star. (Correct)



They are the envelopes that form when blue stragglers merge.

26. When the outer envelope of a red giant escapes, the remaining carbon core is called a



white dwarf. (Correct)



black dwarf.



planetary nebula.



brown dwarf.



black hole.

27. Which statement about the stages of starbirth is false?



The T-Tauri wind is prevalent in stage 5.



By stage 7, the star has reached the main sequence.



At stage 1, only the cloud exists.



By stage 3, the star has formed a photosphere.



nuclear reactions begin in the core by stage 4. (Correct)

28. Which is characteristic of globular star clusters?



no remaining main sequence stars, but millions of white dwarfs



only brown dwarfs in a yellow ball 100 ly across



a mix of old and young stars, about 100,000 ly across



old age and hundreds of thousands of stars, only about 30 ly wide (Correct)



bright blue main sequence stars, and thousands of them...