evolution-of-stars.html

Evolution of stars

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.

1. The hydrogen lines in spectral type A stars
a. are most narrow for supergiants.
b. are most narrow for main sequence stars.
c. can not be used to estimate the luminosity of the star.
d. are very weak and difficult to see.
e. are useful in determining the apparent magnitude of the star.

2. Parallax would be easier to measure if
a. Earth's orbit were larger.
b. the stars were farther away.
c. Earth moved faster along its orbit.
d. all of these
e. none of these

3. Absolute visual magnitude is
a. the apparent magnitude of a star observed from Earth.
b. the luminosity of a star observed from a distance of 1000 pc.
c. the apparent magnitude of a star observed from a distance of 10 pc.
d. the luminosity of a star observed from Earth.
e. c and d

4. A star's luminosity depends only on the star's
a. distance and diameter.
b. temperature and distance.
c. distance.
d. temperature and diameter.
e. apparent magnitude.

5. In an H-R Diagram, stars with the smallest radius are found in the __________ of the diagram.
a. center
b. upper left corner
c. upper right corner
d. lower left corner
e. lower right corner

6. In the H-R diagram, 90 percent of all stars are
a. in the giant region.
b. in the supergiant region.
c. among the B stars.
d. among the G stars.
e. on the main sequence.

7. We know that giant stars are larger in diameter than the sun because
a. they are more luminous but have about the same temperature.
b. they are less luminous but have about the same temperature.
c. they are hotter but have about the same luminosity.
d. they are cooler but have about the same luminosity.
e. they have a larger absolute magnitude than the sun.

8. Giant stars are

I. more luminous than the sun.
II. larger in diameter than the sun.
III. cooler than B stars.
IV. located above the main sequence stars in the H-R diagram.

a. I & II
b. II & IV
c. I, II, & IV
d. II, III, & IV
e. I, II, III, & IV

9. Compared with the spectral lines in the solar spectrum, lines in a supergiant spectrum are
a. more narrow.
b. broader.
c. weaker.
d. stronger.
e. b and c

10. The most common stars are
a. supergiants.
b. giants.
c. upper main sequence stars.
d. white dwarfs.
e. lower main sequence stars.

11. The __________ of a star is a measure of the total energy radiated by the star in one second.
a. absolute visual magnitude
b. apparent visual magnitude
c. luminosity class
d. spectral type
e. luminosity

12. Sheat is an M2 II star. Based on this information which of the following are true?

I. Sheat has a surface temperature less than the sun.
II. Sheat has a diameter that is greater than that of the sun.
III. Sheat is more luminous than the sun.
IV. Sheat is located near the upper left hand corner in the HR diagram.

a. I & II
b. II & IV
c. II, III, & IV
d. I, II, & III
e. I, II, III, & IV

13. d Circini is an O 8.5 V star. Based on this information which of the following are true?

I. d Circini has a surface temperature less than the sun.
II. d Circini has a diameter that is greater than that of the sun.
III. d Circini is more luminous than the sun.
IV. d Circini is located near the upper left hand corner in the HR diagram.

a. I & II
b. II & IV
c. II, III, & IV
d. I, II, & III
e. I, II, III, & IV

14. To determine the period of a visual binary, we must measure
a. brightness.
b. position.
c. wavelengths.
d. luminosity.
e. temperature.

15. In a binary system, the more massive star
a. is at the center of mass.
b. is farthest from the center of mass.
c. is nearest the center of mass.
d. follows the largest orbit.
e. shows a larger Doppler shift in its spectral lines.

16. Spectroscopic binaries are difficult to analyze because
a. we can't measure the radial velocities of each star in the system.
b. we can't see the shape of the orbit.
c. we can't find the diameters of the stars.
d. we can't determine the luminosities of the stars.
e. the Doppler shift is not measurable.

Figure 8-1

17. Which star in Figure 8-1 above is most like the sun?
a. Alnilam
b. Antares
c. Arcturus
d. HR 5337
e. Sirius B

18. Which star in Figure 8-1 above has the greatest surface temperature?
a. Alnilam
b. Antares
c. Arcturus
d. HR 5337
e. Sirius B

19. Which of the stars in Figure 8-1 above has the largest absolute visual magnitude?
a. Alnilam
b. Antares
c. Arcturus
d. HR 5337
e. Sirius B

20. An eclipsing binary will
a. be more luminous than a visual binary.
b. always be a spectroscopic binary.
c. give off most of its light in the infrared.
d. show a constant Doppler shift in its spectral lines.
e. show two stars with variable proper motion.

21. If we can solve the orbital motion of an eclipsing binary, we can find
a. the masses of the stars.
b. the diameters of the stars.
c. the distance to the binary.
d. all of the above
e. both a and b

22. Which of the following best obey the mass-luminosity relation?
a. main sequence stars
b. giant stars
c. supergiant stars
d. white dwarfs
e. all of the above

23. Which of the following stars is most dense?
a. a supergiant star
b. a main sequence star
c. a giant star
d. a white dwarf
e. the sun

24. A spectroscopic binary shows periodic variations in its
a. radial velocity.
b. proper motion.
c. brightness.
d. mass.
e. spectral type.

25. Stars on the main sequence with the greatest mass
a. are spectral type M stars.
b. are spectral type O stars.
c. are located at the bottom of the main sequence in the HR diagram.
d. have masses very similar to the sun.
e. both b and c

26. The star Algol is
a. an astrometric binary.
b. a single line spectroscopic binary.
c. a visual binary.
d. an eclipsing binary.
e. none of the above

27. The total mass of a binary system can be calculated from
a. the ratio of the angular separation from the center of mass of each of the stars.
b. the distance to the binary and its radial velocity.
c. the semi major axis and period of the orbit.
d. the radial velocities of the two stars.
e. the time required for the small star to eclipse the larger star.

28. The diagram below illustrates two stars in a visual binary system and the center of mass of this system. Based on this diagram, what is the ratio of the mass of star A to the mass of star B?

a. 2 to 1
b. 1 to 2
c. 2 to 3
d. 3 to 2
e. 1 to 3

29. If a star has a parallax of 0.02 seconds of arc, then its distance is
a. 20 pc
b. 50 pc
c. 2 pc
d. 5 pc
e. 500 pc

30. If a star with an absolute magnitude of -5 has an apparent magnitude of +5, then its distance is
a. 1 pc.
b. 10 pc.
c. 100 pc.
d. 1000 pc
e. 10,000 pc.

31. An eclipsing binary has been analyzed and it has been determined that the ratio of the mass of star A to the mass of star B is 6 and the total mass of the two stars is 26 solar masses. What are the masses of star A and star B.
a. Star A has a mass of 1 solar mass and star B has a mass of 6 solar masses.
b. Star A has a mass of 20 solar mass and star B has a mass of 6 solar masses.
c. Star A has a mass of 31.2 solar mass and star B has a mass of 5.2 solar masses.
d. Star A has a mass of 22.3 solar mass and star B has a mass of 3.7 solar masses.
e. The masses of star A and star B cannot be determined from the information given.

32. What is the total mass of a binary star system with P = 20 yr and a = 10 AU?
a. 2 solar masses
b. 2.5 solar masses
c. 0.5 solar mass
d. 80 solar masses
e. 0.4 solar mass

33. The diagram below shows the radial velocity curve of a double-line spectroscopic binary. Based on this radial velocity curve, which of the following statements is correct?

a. Star A is twice the mass of star B.
b. Star B is twice the mass of star A.
c. Star A is ten times the mass of star B.
d. Star B is ten times the mass of star A.
e. Star A and Star B have the same mass.

34. In the light curve below, what is the period of the binary?

a. 5 days
b. 32.5 days
c. 7.5 days
d. 42.5 days
e. 50 days

35. At what point in the light curve below is the cool star in front of the hotter star?

a. 1
b. 2
c. 3
d. 4
e. 5

Table 8-1

Star mv Mv d(pc) Parallax (sec or arc) Spectral Type

65 tau 4.2 0.025 A7IV

HR4621 2.6 -0.3 B2IV

a Pic 1.8 20 A7V

58 Ori -6.0 0.005 M21

HR 2491 -1.5 2.5 A1V

36. Which star in Table 8-1 above would appear the faintest in the night sky?
a. 65 Tau
b. HR 4621
c. a Pic
d. 58 Ori
e. HR 2491

37. Which star in Table 8-1 above has the greatest luminosity?
a. 65 Tau
b. HR 4621
c. a Pic
d. 58 Ori
e. HR 2491

38. Which star in Table 8-1 above is the closest to Earth?
a. 65 Tau
b. HR 4621
c. a Pic
d. 58 Ori
e. HR 2491

39. Which star in Table 8-1 above has the greatest surface temperature?
a. 65 Tau
b. HR 4621
c. a Pic
d. 58 Ori
e. HR 2491

40. Which star in Table 8-1 above has the greatest diameter?
a. 65 Tau
b. HR 4621
c. a Pic
d. 58 Ori
e. HR 2491

Table 8-2

Star mv Mv d(pc) Parallax (sec or arc) Spectral Type

d Cen 0.026 B2 IV

HR4607 0.039 G8 III

H4758 20 G0 V

HD39801 0.005 M21

9CMa 2.5 A1V

41. Which star in Table 8-2 above is the closest to Earth?
a. d Cen
b. HR 4607
c. HR 4758
d. HD 39801
e. 9 CMa

42. Which star in Table 8-2 above has the greatest surface temperature?
a. d Cen
b. HR 4607
c. HR 4758
d. HD 39801
e. 9 CMa

43. Which star in Table 8-2 above has the greatest diameter?
a. d Cen
b. HR 4607
c. HR 4758
d. HD 39801
e. 9 CMa

44. If the orbital velocity of an eclipsing binary is 97 km/sec and the smaller star is completely eclipsed in 2 hours, what is the diameter of the smaller star?
a. 175,000 km
b. 350,000 km
c. 194 km
d. 700,000 km
e. 4656 km

45. A 2 solar mass star on the main sequence would have a luminosity of approximately __________ solar luminosities.
a. 2
b. 4
c. 11
d. 0.5
e. 0.25

46. Protostars are difficult to observe because
a. the protostar stage is very short.
b. they are surrounded by cocoons of gas and dust.
c. they radiate mainly in the infrared.
d. all of the above
e. they are all so far away that the light hasn't reached us yet.

47. The nuclear reactions in a star's core remain under control so long as
a. luminosity depends on mass.
b. pressure depends on temperature.
c. density depends on mass.
d. weight depends on temperature.
e. temperature depends on mass.

48. Interstellar gas clouds may collapse to form stars if they
a. have very high temperatures.
b. encounter a shock wave.
c. rotate rapidly.
d. are located near main sequence spectral type K and M stars.
e. all of the above.

49. __________ are small luminous nebulae excited by nearby young stars.
a. T Tauri stars
b. Herbig-Haro objects
c. O associations
d. Bok Globule
e. Giant molecular clouds

50. Opacity is
a. the balance between the pressure and force of gravity inside a star.
b. the force that binds protons and neutrons together to form a nucleus.
c. the force that binds an electron to the nucleus in an atom.
d. a measure of the ease with which photons can pass through a gas.
e. the temperature and density at which a gas will undergo thermonuclear fusion.

51. The Great Nebula in Orion
a. is a Herbig-Haro object.
b. is a reflection nebula.
c. is an emission nebula.
d. contains only young low mass stars.
e. is believed to be about 5 billion years old.

52. __________ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.
a. The CNO cycle
b. The proton-proton chain
c. Hydrostatic equilibrium
d. The neutrino process
e. none of the above

53. The diagram below is an HR diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?

a. 1
b. 2
c. 3
d. 4
e. 5

54. In the proton-proton chain
a. no neutrinos are produced.
b. energy is released because a helium nucleus has a greater mass than a hydrogen nucleus.
c. no photons are produced.
d. carbon serves as a catalyst for the nuclear reaction.
e. energy is produced in the form of gamma rays and the velocity of the created nuclei.

55. The carbon-nitrogen-oxygen cycle
a. operates at a slightly lower temperature than the proton-proton chain.
b. is most efficient in star less massive than the sun.
c. occurs when carbon and oxygen combine to form nitrogen, which produces energy.
d. produces the energy responsible for bipolar flows.
e. combines four hydrogen nuclei to form one helium nucleus, which produces energy.

56. What causes the outward pressure that balances the inward pull of
gravity in a star?
a. The outward flow of energy.
b. The opacity of the gas.
c. The temperature of the gas
d. The density of the gas
e. c and d

57. The free-fall contraction of a molecular cloud
a. can be initiated by shock waves from supernovae.
b. can be initiated by nearby spectral type G stars.
c. can be initiated by the rotation of the cloud.
d. causes the cloud to become transparent to ultraviolet radiation.
e. causes the particles in the cloud to decrease the speed with which they move.

58. Convection is important in stars because it
a. increases the temperature of the star.
b. mixes the gases of the star.
c. transports energy outward in the star.
d. carries the neutrinos to the surface of the star where they can escape.
e. b and c

59. __________ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star and a strong wind from the warm protostar ejects material from its poles.
a. An emission nebula
b. Hydrostatic equilibrium
c. The proton-proton chain
d. The thermonuclear fusion of hydrogen
e. A bipolar flow

60. Which of the following is not evidence of the existence of an interstellar medium?
a. extinction
b. narrow calcium lines in the spectra of O and B stars
c. reddening
d. dark clouds
e. molecular bands in the spectra of cool stars

61. Molecular clouds can be observed
a. using infrared telescopes to detect ionized gas in the clouds.
b. using x-ray telescope to observe the x-ray radiation from the molecules in the cloud.
c. using radio telescopes to observe the CO emission from the clouds.
d. by looking for blue wispy regions near star clusters.
e. by looking for the 21-cm radiation from hydrogen.

62. The main sequence has a limit at the lower end because
a. low mass stars form from the interstellar medium very rarely.
b. low mass objects are composed primarily of solids, not gases.
c. pressure does not depend on temperature in degenerate matter.
d. the lower limit represents when the radius of the star would be zero.
e. there is a minimum temperature for hydrogen fusion.

63. There is a mass-luminosity relation because
a. hydrogen fusion produces helium.
b. stars expand when they become giants.
c. stars support their weight by making energy.
d. the helium flash occurs in degenerate matter.
e. all stars on the main sequence have about the same radius.

64. Due to the dust in the interstellar medium, a star will appear to an observer on Earth to be
a. brighter and cooler than it really is.
b. brighter and hotter than it really is.
c. fainter and cooler than it really is.
d. fainter and hotter than it really is.
e. unchanged in brightness or apparent color.

65. The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
a. 1 M
b. 60 M .
c. 0.5 M .
d. 0.08 M .
e. 0.001 M .

66. What is the lifetime of a 10 M star on the main sequence?
a. 3.2 x 10⁷ years
b. 320 years
c. 3.2 x 10¹² years
d. 1 x10⁹ years
e. 1 x1011 years

67. __________ require(s) that a young hot star (T 25,000 K) be relatively nearby.
a. Emission nebulae
b. HI regions
c. Molecular clouds
d. The hot gas of the interstellar medium
e. 21 cm radiation

68. The extinction of starlight due to the interstellar medium

I. is the greatest in the ultraviolet.
II. is the greatest in the infrared.
III. is caused by ionized hydrogen.
IV. is caused by dust particles.

a. I & III
b. II & III
c. I & IV
d. II & IV
e. only IV

69. __________ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.
a. HI regions
b. HII regions
c. Emission nebulae
d. Bok globules
e. Reflection nebulae

70. Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
a. the lines are blue shifted.
b. the lines are red shifted.
c. the lines are extremely broad.
d. the lines are extremely narrow.
e. the lines are much darker than the stellar lines.

71. Stars are born in
a. reflection nebulae.
b. dense molecular clouds.
c. HII regions.
d. the intercloud medium.
e. the local bubble.

72. Absorption lines due to interstellar gas
a. are wider than the lines from stars because the gas is hotter than most stars.
b. are more narrow than the lines from stars because the gas has a lower pressure than stars.
c. indicate that the interstellar medium contains dust.
d. indicate that the interstellar medium is expanding away from the sun.
e. none of the above

73. As a star exhausts hydrogen in its core, it
a. becomes hotter and more luminous.
b. becomes cooler and more luminous.
c. becomes hotter and less luminous.
d. becomes cooler and less luminous.
e. it becomes larger in radius and hotter.

74. A star will experience a helium flash if
a. it is more massive than about 6 solar masses.
b. its core contains oxygen and helium.
c. its mass on the main sequence was less than 0.1 solar masses.
d. it is a supergiant.
e. its core is degenerate when helium ignites.

75. In degenerate matter
a. pressure depends only on the temperature.
b. temperature depends only on density.
c. pressure does not depend on temperature.
d. pressure does not depend on density.
e. b and c

76. Giant and supergiant stars are rare because
a. they do not form as often as main sequence stars.
b. the giant and supergiant stage is unstable.
c. the giant and supergiant stage is very short.
d. helium is very rare.
e. helium flash destroys many of the stars before they can become giants and supergiants.

77. Star cluster are important to our study of stars because
a. all stars formed in star clusters.
b. the sun was once a member of a globular cluster.
c. they give us a method to test the our theories and models of stellar evolution.
d. they are the only objects that contain Cepheid variables.
e. all of the above

78. What is the approximate age of the star cluster in the diagram below?

a. 2 million years
b. 2 billion years
c. 10 billion years
d. 100 billion years
e. The age of the cluster can not be estimated from an HR diagram of the cluster.

79. The triple alpha process
a. controls the pulsations in Cepheid variable stars.
b. is the nuclear fusion of hydrogen to helium in massive stars.
c. is the process that produces the neutrinos we receive from the sun.
d. requires a temperature of about 5,000,000 K to operate
e. occurs during helium flash.

80. The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
a. 1 M .
b. 60 M .
c. 0.5 M .
d. 0.08 M .
e. 0.001 M .

81. Which of the following nuclear fuels does a one solar mass star use over the course of its entire evolution?
a. hydrogen
b. hydrogen and helium
c. hydrogen, helium, and carbon
d. hydrogen, helium, carbon, and neon
e. hydrogen, helium, carbon, neon, and oxygen.

82. Helium flash occurs
a. because helium is very explosive and cannot be controlled when the 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 M .
e. none of the above

83. Stars in a star cluster
a. all have the same age.
b. all have the same chemical composition.
c. all have the same luminosity.
d. all of the above
e. a and b above

84. If the stars at the turnoff point of a cluster have a mass of 3 M , what is the age of the cluster?
a. 3.0 x 10¹⁰ years
b. 3.3 x 10⁹ years
c. 6.4 x10⁸ years
d. 1.6 x 10¹¹ years
e. The age of a star cluster can not be determined from the mass of stars at the turnoff point.

85. In the diagram below, which point indicates the location on the HR diagram of a one solar mass star when it undergoes helium flash?

a. 1
b. 2
c. 3
d. 4
e. 5

86. The lowest-mass stars cannot become giants because
a. they do not contain helium.
b. they rotate too slowly.
c. they cannot heat their centers hot enough.
d. they contain strong magnetic fields.
e. they never use up their hydrogen.

87. A planetary nebula is
a. the expelled outer envelope of a medium mass star.
b. produced by a supernova explosion.
c. produced by a nova explosion.
d. a nebula within which planets are forming.
e. a cloud of hot gas surrounding a planet.

88. The Chandrasekhar limit tells us that
a. accretion disks can grow hot through friction.
b. neutron stars of more than 3 solar masses are not stable.
c. white dwarfs must contain more than 1.4 solar masses.
d. not all stars will end up as white dwarfs.
e. stars with a mass less than 0.5 solar masses will not go through helium flash.

89. A Type I supernova is believed to occur when
a. the core of a massive star collapses.
b. carbon detonation occurs.
c. a white dwarf exceeds the Chandrasekhar limit.
d. the cores of massive stars collapse.
e. neutrinos in a massive star become degenerate and form a shock wave that explodes the star.

90. Massive stars cannot generate energy through iron fusion because
a. iron fusion requires very high density.
b. stars contain very little iron.
c. no star can get hot enough for iron fusion.
d. iron is the most tightly bound of all nuclei.
e. massive stars supernova before they create an iron core.

91. The theory that the collapse of a massive star's iron core produces neutrinos was supported by
a. the size and structure of the Crab nebula.
b. laboratory measurements of the mass of the neutrino.
c. the brightening of supernovae a few days after they are first visible
d. underground counts from solar neutrinos.
e. the detection of neutrinos from the supernova of 1987.

92. Synchrotron radiation is produced by
a. objects with temperature below 10,000 K.
b. high-velocity electrons moving through a magnetic field.
c. cold hydrogen atoms in space.
d. the collapsing cores of massive stars.
e. helium flash.

93. A nova is almost always associated with
a. a very massive star.
b. a very young star.
c. a star undergoing helium flash.
d. a white dwarf in a close binary system.
e. a solar like star that has exhausted its hydrogen and helium.

94. The Algol paradox is explained by considering
a. the degenerate nature of the hydrogen on the surface of the white dwarf.
b. synchrotron radiation
c. the rate of expansion of the shock wave inside the supernova.
d. the rotation rate of a neutron star.
e. mass transfer between the two stars in a binary system.

95. Stars with masses between 0.4 M and 4 M
a. undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
b. undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
c. produce type-I supernovae after they exhaust their nuclear fuels.
d. produce type-II supernovae after they exhaust their nuclear fuels.
e. undergo carbon detonation.

96. A type-II supernova
a. occurs when a white dwarf's mass exceeds the Chandrasekhar limit.
b. is the result of helium flash.
c. is characterized by a spectrum that shows hydrogen lines.
d. occurs when the iron core of a massive star collapses.
e. c and d

97. Synchrotron radiation is produced
a. in planetary nebulae.
b. by red dwarfs.
c. massive stars as their iron core collapses.
d. in supernova remnants.
e. neutrinos

98. When material expanding away from a star in a binary system reaches the Roche surface
a. the material will start to fall back toward the star.
b. all of the material will accrete on to the companion.
c. the material is no longer gravitationally bound to the star.
d. the material will increase in temperature an eventually undergo thermonuclear fusion.
e. c and d

99. A white dwarf is composed of
a. hydrogen nuclei and degenerate electrons.
b. helium nuclei and normal electrons.
c. carbon and oxygen nuclei and degenerate electrons.
d. degenerate iron nuclei.
e. a helium burning core and a hydrogen burning shell.

100. A planetary nebula
a. produces an absorption spectrum.
b. produces an emission spectrum.
c. is contracting to form planets.
d. is contracting to form a star.
e. is the result of carbon detonation in a 1 M star.

101. If the theory that novae occur in close binary systems is correct, then novae should
a. produce synchrotron radiation.
b. occur in regions of star formation.
c. not occur in old star clusters.
d. all be visual binaries.
e. repeat after some interval.

102. As a white dwarf cools its radius will not change because
a. pressure due to nuclear reactions in a shell just below the surface keeps it from collapsing.
b. pressure does not depend on temperature for a white dwarf because the electrons are degenerate.
c. pressure does not depend on temperature because the white dwarf is too hot.
d. pressure does not depend on temperature because the star has exhausted all its nuclear fuels.
e. material accreting onto it from a companion maintains a constant radius.

103. The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?

a. less than 50
b. 50
c. 150
d. 250
e. more than 250

Completion
Complete each sentence or statement.

104. The parallax of the star 75 Leo is 0.10 and its apparent visual magnitude is +5.18. The absolute visual magnitude of 75 Leo is
105. A G2 I star is in diameter and luminous than the sun.

106. can be used to determine the distance to a star when the spectrum of the star can be used to determine its spectral type and luminosity class.

107. Luminosity class IV objects are known as

108. On the HR diagram below, indicate the location of the white dwarf stars.

109. For stars on the main sequence, the luminosity can be estimated by the formula L =
110. The masses and diameters of each star in the binary can be determined from

binaries.
111. Below is a radial velocity curve for a spectroscopic binary. Which of the stars is most massive?

112. If we divide the mass of a star by its volume we calculate the star's

113. is the resistance of a gas to the flow of radiation.
114. The condition of means that the force due to gravity pushing down on a layer is exactly equal to the pressure pushing outward on that layer.
115. Stars with masses greater than 1.1 solar masses use the to convert hydrogen into helium and produce energy
116. Energy transport by is important when photons cannot readily travel through a gas.

117. appear reddish in color due to the light emitted by the Balmer series of the hydrogen atom.
118. The pressure of an interstellar gas cloud depends on the clouds and

119. A gas in which the pressure no longer depends on the temperature of the gas is said to be
120. The age of a star cluster can be determined from the of the cluster.
121. The maximum mass of a white dwarf is solar masses.
122. A(n) is the expulsion of the outer layers of a moderate mass star that has a degenerate carbon and oxygen core.
123. Electrons moving in a strong magnetic field emit radiation.
124. Mass can flow from one star in a binary system to its companion through the firstpoint.

True/False
Indicate whether the sentence or statement is true or false.
125. A star whose parallax is 0.01 seconds arc is at a distance of 1000 pc.

126. The absolute magnitude of a star is the apparent magnitude it would have if it were 10 pc from Earth.

127. The location of a star in the HR diagram indicates its temperature and intrinsic brightness.

128. Absorption lines in the spectra of supergiant stars are broader than the same spectral lines in main sequence stars of the same spectral type.

129. Giant stars are members of luminosity class III.

130. If a star is twice as hot as the sun and only half the sun's diameter, it will be less luminous than the sun.

131. The method of spectroscopic parallax cannot be applied to stars beyond about 100 pc.

132. The most common kinds of stars are low-luminosity stars.
133. Supergiants are about as common as the sun.

134. White dwarfs have such a low luminosity that even the nearest white dwarfs are not visible to the naked eye.

135. To observe a visual binary, we must measure radial velocities.

136. The more massive star in a binary system is always farthest from the center of mass.

137. If a binary system has a period of 4 years and a separation of 5 AU, then the total mass is 7.8 solar masses.

138. To observe a spectroscopic binary, we must be able to see both stars individually.

139. We can find the masses and diameters of stars that are in eclipsing binary systems.

140. When we see a binary system producing eclipses, we know that the orbit is nearly edge-on.

141. The most massive main-sequence stars are the M stars.
142. The densest stars in the H-R diagram are the white dwarfs.

143. Some young star clusters contain large numbers of T Tauri stars.

144. Ninety percent of all stars fuse helium to form carbon and lie on the main sequence.

145. Nuclear fusion in stars is controlled by the dependence of density on mass.

146. The sun has a core in which energy travels outward primarily by radiation.
147. The sun makes most of its energy by the CNO cycle.

148. Energy flows by radiation or convection inside stars but almost never by conduction.

149. Hydrostatic equilibrium refers to the balance between weight and pressure.

150. The Orion region contains young main sequence stars and an emission nebula, but the original molecular cloud they formed out of has been dispersed.

151. T Tauri stars are believed to be young, high mass main sequence stars.

152. The dust in the interstellar medium can make distant stars look redder than they really are.

153. Bok globules are small, dark fragments of the interstellar medium.

154. The thermal motions of the atoms in a gas cloud can make it collapse to form a protostar.

155. Molecular clouds are mapped using CO instead of hydrogen because CO is much more abundant than hydrogen in molecular clouds.

156. HII regions are found near stars cooler than 25,000 K because large amounts of ultraviolet photons would destroy the hydrogen atoms in the gas.

157. The pressure of a gas depends on the temperature and density of the gas.

158. Stars swell into giants when hydrogen is exhausted in their centers.
159. The helium flash is the cause of some supernovae.

160. Helium fusion does not begin until the star has entered the giant region of the H-R diagram.

161. Even in degenerate matter, pressure depends on temperature.

162. Giant and supergiant stars are rare because that stage of stellar evolution is short.

163. Young star clusters have bluer turn-off points than old clusters.

164. Planetary nebulae are sites of planet formation.

165. Stars less massive than 0.4 solar mass never become giant stars.
166. Once a star ejects a planetary nebula, it becomes a white dwarf.

167. No known white dwarf has a mass greater than the Chandrasekhar limit.

168. Because more massive stars have more gravitational energy, they can fuse heavier nuclear fuels.

169. The sun will eventually become a supernova.

170. Type II supernovae are believed to occur when the cores of massive stars collapse.

171. Synchrotron radiation occurs when high speed electrons move through a magnetic field.

172. A Type II supernova produces a planetary nebula.
173. A nova destroys the star and leaves behind a white dwarf.

Star	mv	Mv	d(pc)	Parallax (sec or arc)	Spectral Type
65 tau	4.2			0.025	A7IV
HR4621	2.6	-0.3			B2IV
a Pic		1.8	20		A7V
58 Ori		-6.0		0.005	M21
HR 2491	-1.5		2.5		A1V