Astro exam

Study Guide for Final Exam (Chapters: 12, 13, 14, 15, 16)

Name: ___________________________________ Section: _____________

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

Chapter 12: Surveying Stars 1) A star’s luminosity is

2) A star’s luminosity depends primarily on its _______________ and ______________________________.

3) A star’s brightness depends on its __________________ and ______________________________.

4) Write down spectral sequence from hottest star to coldest stars ______________________________.

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

5) Spectral type of a star determines its ______________________________. A) core temperature. B) surface temperature. C) mass D) radius. E) Luminosity

6) If the distance between us and a star is doubled, with everything else remaining the same, its luminosity A) is decreased by a factor of four, but its apparent brightness remains the same. B) is decreased by a factor of four, and its apparent brightness is decreased by a factor of four. C) remains the same, but its apparent brightness is decreased by a factor of two. D) remains the same, but its apparent brightness is decreased by a factor of four. E) is decreased by a factor of two, and its apparent brightness is decreased by a factor of two.

7) If Star A is closer to us than Star B, then Star A’s parallax angle is ________. A) smaller than that of Star B B) fewer parsecs than that of Star B C) equal to that of Star B since parallax is the same for all stars, regardless of their distance D) larger than that of Star B

8) Which of the following statements about spectral types of stars is true? A) A star with spectral type F2 is hotter than a star with spectral type F3. B) A star with spectral type A is cooler than a star with spectral type B. C) The spectral type of a star can be used to determine its surface temperature. D) The spectral type of a star can be used to determine its color. E) All of the above are true.

9) Which of the stars (spectral type) below is hottest? A) G B) F C) M D) K

Descriptive Astronomy 201 Spring 2019

MATCHING. Choose the item in column 2 that best matches each item in column 1.

Question 10- 13 is based on spectral types of stars. 10) What is the spectral type of the Sun?

11) What is the spectral type of the hottest and bightest stars?

12) What is the spectral type of the coldest and dimmerst stars?

13) What is the most common type (spectral type) of main-sequence star?

14) What is the spectral type of main-sequence stars which have longer life time?

A) M

B) O

C) A

D) F

E) G

F) K

G) B

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

15) To calculate the masses of stars in a binary system, we must measure their A) absolute magnitudes and luminosities B) luminosities and distance from Earth C) orbital period and average orbital distance D) spectral types and distance from Earth

MATCHING. Choose the item in column 2 that best matches each item in column 1.

16) What is the luminosity class refers to stars on the main sequence?

17) What is the luminosity class refers to supergiants?

18) What is the luminosity class refers to giants?

A) I

B) II

C) III

D) IV

E) V

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MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

19) If we measure the light emitted by a Sun-like (G spectral type) main sequence star for several weeks and observe a graph of brightness verses time as the graph below.

Which of the graph below show how the graph of brightness verses time would look for an O spectral type star?

A) B)

C) D)

Use the diagram below to answer from Q uestion 11-15. The sketch below shows groups of stars on the H-R diagram, labeled (a) through (e); note that (a) represents the entire main sequence while (c) and (d) represent only small parts of the main sequence.

20) Which group represents stars that are cool and dim? A) a B) b C) c D) d E) e

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21) Which group represents stars that are hot, extremely bright and emit most of their radiation as ultrviolet? A) a B) b C) c D) d E) e

22) Which group represents stars of the largest radii? A) a B) b C) c D) d E) e

23) Which group represents stars fusing hydrogen in their cores? A) a B) b C) c D) d E) e

24) Which group represents white dwarfs which have no ongloing nuclear fusion? A) a B) b C) c D) d E) e

25) Which group represents most massive stars? A) a B) b C) c D) d E) e

26) Which main sequence stars have longer life time? A) O B) B C) M D) K E) G

27) What is the common trait of all main-sequence stars? A) They all have approximately the same mass. B) They generate energy through hydrogen fusion in their core. C) They are all spectral type G. D) They are in the final stage of their lives.

28) Which of the following statements about star clusters is/are true? A) All stars in the cluster have approximately the same mass. B) All stars in the cluster are approximately the same age. C) All stars in the cluster will evolve similarly. D) All stars in the cluster are at same distance from Earth. E) There is an approximately equal number of all spectral type stars in the cluster.

29) The age of stars in a cluster can be determined by A) finding spectroscopic binaries in the cluster. B) fitting the position of the main sequence to the Sun. C) determining the main-sequence turnoff point. D) counting the number of stars in each spectral class. E) finding pulsating variable stars in the cluster.

30) According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

A) Its apparent brightness will increase by a factor of 9. B) Its apparent brightness will increase by a factor of 3. C) Its apparent brightness will decrease by a factor of 3. D) Its apparent brightness will decrease by a factor of 9.

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Chapter 13: Star stuffs 31) What is the fate of an isolated brown dwarf?

A) It will become a neutron star. B) It will remain as a brown dwarf forever. C) It will slowlybecome a main-sequence star D) It will become a white dwarf.

32) What is a protostar? A) a star that is still in the process of forming B) a star in its final stage of life C) an intermediate-mass star D) a main-sequence star

33) What is a planetary nebula? A) the expanding shell of gas that is left when a white dwarf explodes as a supernova B) the molecular cloud from which planets form C) the expanding shell of gas that is no longer gravitationally bound to the core of a star D) a disk of gas surrounding a protostar that may form into planets

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

34) What is the approximate range of masses that newborn main-sequence stars can have?

35) What is the approximate range of masses that low-mass stars can have?

36) What is the approximate range of masses that high-mass stars can have?

37) What is the correct sequence which describes the stages of life for a low- mass star? red giant protostar main-sequence white dwarf

38) What is the correct sequence which describes the stages of life for a high- mass star? red supergiant protostar main-sequence neutron star or a blackhole

39) What kind of gas cloud is most likely to give birth to stars?

40) What types of stars end their lives with supernovae?

41) How does a low-mass stars end its life?

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MATCHING. Choose the item in column 2 that best matches each item in column 1.

42) What is a low mass star left behind finally?

43) A low mass star spend most of its lifetime as a

44) After a supernova, what is a high-mass star left behind?

A) white dwarf

B) a black hole

C) main-sequence star

D) red giant

E) either a neutron star or a black hole

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

45) Why is Supernova 1987A particularly important to astronomers? A) It provided the first evidence that neutron stars exist. B) It was the nearest supernova detected in nearly 400 years. C) It provided the first observational evidence that supernovae actually occur. D) It occurred only a few dozen light-years from Earth.

46) A spinning neutron star has been observed at the center of a ________. A) planetary nebula B) protostar C) red supergiant D) supernova remnant

MATCHING. Choose the item in column 2 that best matches each item in column 1.

47) You observe a red giant star. What is happening to that star?

48) What is happening to a main-sequence star?

49) You observe a star which is in the horizonal branch of the H-R diagram. What is happening to that star?

A) fusing hydrogen in its core.

B) fusing hydrogen in a shell around its core.

C) fusing helium in a shell around its core.

D) fusing helium in its core.

E) fusing carbon in its core.

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

50) Carbon fusion occurs in high-mass stars but not in low-mass stars because ________. A) the cores of low-mass stars never get hot enough for carbon fusion B) the cores of low-mass stars never contain significant amounts of carbon C) only high-mass stars do fusion by the CNO cycle D) carbon fusion can occur only in the stars known as carbon stars

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51) Why are the very lowest mass stars unable to fuse helium in their cores? A) Their cores will bypass helium fusion and use the CNO cycle instead. B) Their cores are supported by the pressure of electrons repelling each other. C) Their cores will never get hot enough to fuse helium. D) Their cores are primarily composed of helium when they form.

52) In which wavelength region(s) would we need to carry out observations in order to study the accretion disk around a white dwarf in a binary system?

A) infrared and radio light B) radio and visible light C) X-ray and ultraviolet light D) gamma ray and X-ray light E) visible and infrared light

MATCHING. Choose the item in column 2 that best matches each item in column 1.

Chapter 14: Stellar Graveyard 53) Which of the following is closest in

size (radius) to a white dwarf?

54) Which of the following is closest in mass to a typical white dwarf?

55) Which of the following is closest in size (radius) to a neutron star?

A) a football stadium

B) the Sun

C) a basketball

D) the Earth

E) the Moon

F) a small city

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.

56) What is the upper limit to the mass of a white dwarf?

57) From a physical standpoint, what is a pulsar?

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

58) Imagine comparing a 1.2 solar mass white dwarf to a 1.1 solar mass white dwarf. Which of the following must be true?

A) The 1.2 solar mass white dwarf has a larger radius. B) The 1.2 solar mass white dwarf has a smaller radius.

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59) What causes the radio pulses of a pulsar? A) A black hole near the neutron star absorbs energy and re-emits it as radio waves. B) The neutron star undergoes periodic explosions of nuclear fusion that generate radio pulses. C) The vibration of the neutron star. D) The neutron star’s orbiting companion periodically eclipses the radio waves that the neutron star emits. E) As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the

Earth, we observe a pulse.

60) How does a black hole form from a massive star? A) A black hole forms when two massive main-sequence stars collide. B) During a supernova, if the mass of the infalling core has enough gravity to overcome neutron degeneracy

pressure, the core will collapse to a black hole. C) If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave behind a

black-hole remnant. D) If enough mass is accreted by a white dwarf star that it exceeds the 1.4 solar mass limit, it will undergo a

supernova explosion and leave behind a black-hole remnant. E) Any star more massive than 1.4 solar masses will undergo a supernova explosion and leave behind a

black hole remnant.

61) What is the basic definition of a black hole? A) a dead star that has faded from view B) an object with gravity so strong that not even light can escape C) an object that absorbs all light and emits radiation based only on its temperature D) any object made from dark matter

62) Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly ________.

A) 10 solar masses B) 1.4 solar masses C) 3 solar masses D) 0.5 solar masses

63) What do we mean by the event horizon of a black hole? A) It is the distance from the black hole at which stable orbits are possible. B) It is the place where X-rays are emitted from black holes. C) It is the very center of the black hole. D) It is the boundary beyond which light cannot escape.

64) The first gravitational waves were detected in 2015 by the LIGO observatories in Washington and Louisiana. What event was thought to cause these gravitational waves?

A) ripples in space-time left over from the Big Bang B) two black holes merging C) two neutron stars merging D) a hypernova

65) What is the leading hypothesis for the origin of short gamma-ray bursts? A) the collision of stars in the dense nuclei of distant galaxies B) very powerful supernovae occurring in distant galaxies C) the collision of two neutron stars or a neutron star with a black hole D) new stars forming in the Milky Way E) supernovae in the Milky Way

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66) According to our modern understanding, what is a nova? A) the sudden formation of a new star in the sky B) the explosion of a massive star at the end of its life C) a rapidly spinning neutron star D) an explosion on the surface of a white dwarf in a close binary system

67) Which of the following observatories is most likely to discover a black hole in a binary system? A) the Chandra X-Ray Observatory B) the SOFIA airborne infrared observatory C) the Arecibo Radio Observatory D) the Hubble Space Telescope

68) Which of the following observatories is most likely to image a black hole in a binary system? A) the SOFIA airborne infrared observatory B) the Hubble Space Telescope C) the Arecibo Radio Observatory D) Event horizon telescope E) the Chandra X-Ray Observatory

Chapter 15 and 16 (will be discuss on Next Tuesday) 69) What kinds of objects lie in the halo of our galaxy?

A) open clusters B) globular clusters C) O and B stars D) molecular clouds E) all of the above

70) What kinds of objects lie in the disk of our galaxy? A) O and B stars B) old K and M stars C) open clusters D) gas and dust E) all of the above

71) Where does most star formation occur in the Milky Way today? A) in the bulge B) in the spiral arms C) in the halo D) in the galactic center E) uniformly throughout the galaxy

72) What kind of object do we think lies at the center of the Milky Way Galaxy? A) a dense cluster of young, hot stars B) a gigantic X-ray binary system C) an enormous collection of dark matter, explaining why we detect no light at all from the galactic center D) a 3 to 4 million solar mass black hole

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73) What is an ionization nebula? A) a name sometimes used to describe spiral galaxies besides the Milky Way B) a region of very hot, low-density gas surrounding a recent supernova C) a clump of gas that will soon give birth to a new star D) a colorful cloud of gas that glows because it is heated by light from nearby hot stars

74) Which of the following is not one of the three major categories of galaxies? A) elliptical galaxies B) spiral galaxies C) globular galaxies D) irregular galaxies

75) Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms? A) ellipticals B) irregulars C) lenticulars D) all of the above

76) Compared to spiral galaxies, elliptical galaxies are A) bluer and flatter. B) always much smaller. C) redder and flatter. D) bluer and more round. E) redder and more round.

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