Question 1

A globular cluster is a group of stars that has:

Accepted Answer

A) many thousands of members, mostly binary, of different ages. 
B) many thousands of members, all very old, with very few elements heavier than helium. 
C) many thousands of members of different ages but with the same chemical composition. 
D) a few hundred members, often still embedded in the gas from which they were formed. 
A) many thousands of members, mostly binary, of different ages. 
B) many thousands of members, all very old, with very few elements heavier than helium. 
C) many thousands of members of different ages but with the same chemical composition. 
D) a few hundred members, often still embedded in the gas from which they were formed. B

Question 2

Figure 19-11 of Universe, 11th ed., shows the evolution of a hypothetical open cluster. Is there a time when the most massive stars have become red giants and the least massive stars have not yet reached the main sequence?
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Accepted Answer

A) No, the protostar phase is so short compared to the main-sequence phase that all protostars have reached the main sequence long before any evolve off it. 
B) No, the main-sequence phase is the longest, even for more massive stars, and all stars remain a great while on the main sequence before beginning evolution to red giants. 
C) Yes, after about 30 million years for this cluster, there are both red giants and protostars. 
D) Yes, after 1 billion years the least massive protostars have not yet reached the main sequence, while a few massive main-sequence stars have evolved to become red giants. 
A) No, the protostar phase is so short compared to the main-sequence phase that all protostars have reached the main sequence long before any evolve off it. 
B) No, the main-sequence phase is the longest, even for more massive stars, and all stars remain a great while on the main sequence before beginning evolution to red giants. 
C) Yes, after about 30 million years for this cluster, there are both red giants and protostars. 
D) Yes, after 1 billion years the least massive protostars have not yet reached the main sequence, while a few massive main-sequence stars have evolved to become red giants. C

Question 3

Which group of stars in the H-R diagram would be labeled "zero-age main sequence"?

Accepted Answer

A) stars that have just collapsed from the interstellar medium 
B) stars that are just beginning to convert helium into carbon in their cores 
C) stars that contain no processed elements (elements heavier than hydrogen or helium) 
D) stars that have just started converting hydrogen to helium in their cores 
A) stars that have just collapsed from the interstellar medium 
B) stars that are just beginning to convert helium into carbon in their cores 
C) stars that contain no processed elements (elements heavier than hydrogen or helium) 
D) stars that have just started converting hydrogen to helium in their cores D

Question 4

The star ? Pegasi (in the constellation Pegasus, the Flying Horse) has a spectral luminosity class of B8 V, giving it a surface temperature of about 12,000 K. According to Table 19-1 of Universe, 11th ed., the expected main-sequence lifetime of ? Pegasi is:
?
  ?

Accepted Answer

A) about 400,000 years. 
B) about 400 million years. 
C) much greater than 800 million years. 
D) not defined in any way by the above information. 
A) about 400,000 years. 
B) about 400 million years. 
C) much greater than 800 million years. 
D) not defined in any way by the above information.

Question 5

Immediately following the end of core hydrogen fusion, continued energy flow from the core is created by:

Accepted Answer

A) helium fusion. 
B) the Kelvin-Helmholtz contraction. 
C) radioactivity. 
D) the fusion of carbon, oxygen, and other heavier nuclei. 
A) helium fusion. 
B) the Kelvin-Helmholtz contraction. 
C) radioactivity. 
D) the fusion of carbon, oxygen, and other heavier nuclei.

Question 6

Which of the following statements is NOT TRUE of a globular cluster?

Accepted Answer

A) It contains significant amounts of dust and gas surrounding the stars. 
B) It has a round shape. 
C) It can contain up to a million stars. 
D) It contains only low-mass stars. 
A) It contains significant amounts of dust and gas surrounding the stars. 
B) It has a round shape. 
C) It can contain up to a million stars. 
D) It contains only low-mass stars.

Question 7

A main-sequence star has a certain lifetime, t, because of thermonuclear "burning" of the hydrogen in the core of the star. How is this lifetime on the main sequence related to the mass M and luminosity L of the star? ( $\alpha$ means "proportional to")

Accepted Answer

A) t M/L $\alpha$ 
B) t ML $\alpha$ 
C) t L/M $\alpha$ 
D) t M3.5 $\alpha$ 
A) t M/L $\alpha$ 
B) t ML $\alpha$ 
C) t L/M $\alpha$ 
D) t M3.5 $\alpha$

Question 8

Helium fusion begins in the core of a low-mass star after the helium flash. Where did this helium come from?

Accepted Answer

A) It was part of the original protostar, but before the helium flash, the temperature was not high enough for helium fusion. 
B) It was produced by hydrogen fusion during the main-sequence phase. 
C) The star acquired it from meteor and comet impacts during the main-sequence phase. 
D) It was produced by the helium flash. 
A) It was part of the original protostar, but before the helium flash, the temperature was not high enough for helium fusion. 
B) It was produced by hydrogen fusion during the main-sequence phase. 
C) The star acquired it from meteor and comet impacts during the main-sequence phase. 
D) It was produced by the helium flash.

Question 9

When the stars of the following open clusters are plotted on an H-R diagram, the temperature values for the turning points are approximately: Coma (10,000 K), h + $\chi$ (40,000 K), M67 (7500 K), and Pleiades (20,000 K). Which cluster is oldest?

Accepted Answer

A) Coma 
B) h + $\chi$ 
C) M67 
D) Pleiades 
A) Coma 
B) h + $\chi$ 
C) M67 
D) Pleiades

Question 10

If you examine many main-sequence stars, the lifetimes are different. As the mass of the star under consideration increases, the star's main-sequence lifetime:

Accepted Answer

A) is unaffected, as lifetime depends only on temperature and luminosity and not mass. 
B) increases because the star has more fuel to burn. 
C) increases because more massive stars have cooler surfaces and smaller luminosities. 
D) decreases because larger stars consume their fuel at a larger rate. 
A) is unaffected, as lifetime depends only on temperature and luminosity and not mass. 
B) increases because the star has more fuel to burn. 
C) increases because more massive stars have cooler surfaces and smaller luminosities. 
D) decreases because larger stars consume their fuel at a larger rate.

Question 11

The 12C and 16O, which now form part of living matter, were part of the cold, dark nebula from which the Sun formed. How did they get there?

Accepted Answer

A) They were part of the original Big Bang and thus part of everything formed since then. 
B) They were formed by earlier generations of stars while they were on the main sequence. 
C) They were formed by earlier generations of stars while they were in their red giant phase. 
D) They were formed in an earlier supernova explosion and dissipated through space. 
A) They were part of the original Big Bang and thus part of everything formed since then. 
B) They were formed by earlier generations of stars while they were on the main sequence. 
C) They were formed by earlier generations of stars while they were in their red giant phase. 
D) They were formed in an earlier supernova explosion and dissipated through space.

Question 12

The "turnoff" point for a star cluster is the point in the H-R diagram occupied by the:

Accepted Answer

A) highest-mass main-sequence stars in the cluster. 
B) stars undergoing (or about to undergo) the helium flash. 
C) lowest-mass main-sequence stars in the cluster. 
D) highest-mass stars that have not yet reached the main sequence. 
A) highest-mass main-sequence stars in the cluster. 
B) stars undergoing (or about to undergo) the helium flash. 
C) lowest-mass main-sequence stars in the cluster. 
D) highest-mass stars that have not yet reached the main sequence.

Question 13

What is the expected main-sequence lifetime of a star with a mass of 15 M ? ? (See Table 19-1 of Universe, 11th ed.)
?
  ?

Accepted Answer

A) 10 billion years 
B) less than 1 million years 
C) 3 million years 
D) 15 million years 
A) 10 billion years 
B) less than 1 million years 
C) 3 million years 
D) 15 million years

Question 14

The H-R diagram for open star clusters (See Figure 19-15 of Universe, 11th ed.) shows the Sun at approximately the 10-billion-year mark on the main sequence. What is the meaning of this?
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Accepted Answer

A) The present age of the Sun is approximately 10 billion years. 
B) The Sun will change its position very little on the diagram during the rest of its main sequence lifetime and thus will still be near the 10-billion-year mark when it finishes its hydrogen burning. 
C) The Sun will evolve a considerable distance up the main sequence, toward higher luminosities, before it leaves the main sequence. 
D) The Sun will evolve a considerable distance down the main sequence, toward lower luminosities, before it leaves the main sequence. 
A) The present age of the Sun is approximately 10 billion years. 
B) The Sun will change its position very little on the diagram during the rest of its main sequence lifetime and thus will still be near the 10-billion-year mark when it finishes its hydrogen burning. 
C) The Sun will evolve a considerable distance up the main sequence, toward higher luminosities, before it leaves the main sequence. 
D) The Sun will evolve a considerable distance down the main sequence, toward lower luminosities, before it leaves the main sequence.

Question 15

12C and 16O are among the most important elements in organic matter, including our bodies. What is the source of 12C and 16O in our solar system?

Accepted Answer

A) They were a part of the cold, dark nebula from which the Sun condensed. 
B) They have been produced in the Sun as a part of the Sun's main-sequence nuclear reactions. 
C) These elements were not present in the original solar nebula but have been produced since by radioactive decay. 
D) These elements were present in the original Big Bang and are thus a part of everything formed since then. 
A) They were a part of the cold, dark nebula from which the Sun condensed. 
B) They have been produced in the Sun as a part of the Sun's main-sequence nuclear reactions. 
C) These elements were not present in the original solar nebula but have been produced since by radioactive decay. 
D) These elements were present in the original Big Bang and are thus a part of everything formed since then.

Question 16

A helium flash occurs in the cores of all stars:

Accepted Answer

A) that contain helium. 
B) of more than 2 M ? 
C) of fewer than 2 M ? 
D) that have become red giants. 
A) that contain helium. 
B) of more than 2 M ? 
C) of fewer than 2 M ? 
D) that have become red giants.

Question 17

After the helium flash in a red giant star, the star contracts because:

Accepted Answer

A) energy radiated to space during the helium flash cools the entire star, making it contract. 
B) the electrons in the core become degenerate during the helium flash, reducing the volume occupied by the core. 
C) the helium flash uses most of the helium in the star's core, reducing the energy produced in the core. 
D) the star's deep interior expands and cools during the helium flash, reducing the energy produced by the hydrogen burning shell. 
A) energy radiated to space during the helium flash cools the entire star, making it contract. 
B) the electrons in the core become degenerate during the helium flash, reducing the volume occupied by the core. 
C) the helium flash uses most of the helium in the star's core, reducing the energy produced in the core. 
D) the star's deep interior expands and cools during the helium flash, reducing the energy produced by the hydrogen burning shell.

Question 18

Suppose a Cepheid variable has been identified, and its period of brightness variability is measured to be 30 days. Its apparent magnitude is +23.3. How far away is it? (See Figure 19-21 of Universe, 11th ed.) Note: The Sun's apparent magnitude is -26.7.
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Accepted Answer

A) 3.1 × 104 pc 
B) 4.8 × 106 pc 
C) 6.0 × 107 pc 
D) 8.7 × 109 pc 
A) 3.1 × 104 pc 
B) 4.8 × 106 pc 
C) 6.0 × 107 pc 
D) 8.7 × 109 pc

Question 19

What particular feature of stellar behavior is associated with the fact that a star is on the main sequence in the Hertzsprung-Russell diagram?

Accepted Answer

A) The star is generating internal energy by hydrogen fusion in its core. 
B) The star is slowly shrinking, thereby releasing gravitational potential energy. 
C) The star is generating energy by helium fusion in its core, having stopped hydrogen "burning." 
D) The star has ceased nuclear "burning" and is simply cooling down by emitting radiation. 
A) The star is generating internal energy by hydrogen fusion in its core. 
B) The star is slowly shrinking, thereby releasing gravitational potential energy. 
C) The star is generating energy by helium fusion in its core, having stopped hydrogen "burning." 
D) The star has ceased nuclear "burning" and is simply cooling down by emitting radiation.

Question 20

Which of the following statements is NOT TRUE of a globular cluster?

Accepted Answer

A) It does not contain main-sequence stars. 
B) It can contain up to a million stars. 
C) It has a round shape. 
D) It contains only low-mass stars. 
A) It does not contain main-sequence stars. 
B) It can contain up to a million stars. 
C) It has a round shape. 
D) It contains only low-mass stars.

Exam 19: Stellar Evolution: on and After the Main Sequence

A globular cluster is a group of stars that has:

Figure 19-11 of Universe, 11th ed., shows the evolution of a hypothetical open cluster. Is there a time when the most massive stars have become red giants and the least massive stars have not yet reached the main sequence? ​ ​

Which group of stars in the H-R diagram would be labeled "zero-age main sequence"?

The star ? Pegasi (in the constellation Pegasus, the Flying Horse) has a spectral luminosity class of B8 V, giving it a surface temperature of about 12,000 K. According to Table 19-1 of Universe, 11th ed., the expected main-sequence lifetime of ? Pegasi is: ? ?

Immediately following the end of core hydrogen fusion, continued energy flow from the core is created by:

Which of the following statements is NOT TRUE of a globular cluster?

A main-sequence star has a certain lifetime, t, because of thermonuclear "burning" of the hydrogen in the core of the star. How is this lifetime on the main sequence related to the mass M and luminosity L of the star? ( α\alphaα means "proportional to")

Helium fusion begins in the core of a low-mass star after the helium flash. Where did this helium come from?

When the stars of the following open clusters are plotted on an H-R diagram, the temperature values for the turning points are approximately: Coma (10,000 K), h + χ\chiχ (40,000 K), M67 (7500 K), and Pleiades (20,000 K). Which cluster is oldest?

If you examine many main-sequence stars, the lifetimes are different. As the mass of the star under consideration increases, the star's main-sequence lifetime:

The 12C and 16O, which now form part of living matter, were part of the cold, dark nebula from which the Sun formed. How did they get there?

The "turnoff" point for a star cluster is the point in the H-R diagram occupied by the:

What is the expected main-sequence lifetime of a star with a mass of 15 M ? ? (See Table 19-1 of Universe, 11th ed.) ? ?

The H-R diagram for open star clusters (See Figure 19-15 of Universe, 11th ed.) shows the Sun at approximately the 10-billion-year mark on the main sequence. What is the meaning of this? ​ ​

12C and 16O are among the most important elements in organic matter, including our bodies. What is the source of 12C and 16O in our solar system?

A helium flash occurs in the cores of all stars:

After the helium flash in a red giant star, the star contracts because:

Suppose a Cepheid variable has been identified, and its period of brightness variability is measured to be 30 days. Its apparent magnitude is +23.3. How far away is it? (See Figure 19-21 of Universe, 11th ed.) Note: The Sun's apparent magnitude is -26.7. ​ ​

What particular feature of stellar behavior is associated with the fact that a star is on the main sequence in the Hertzsprung-Russell diagram?

Which of the following statements is NOT TRUE of a globular cluster?

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Figure 19-11 of Universe, 11th ed., shows the evolution of a hypothetical open cluster. Is there a time when the most massive stars have become red giants and the least massive stars have not yet reached the main sequence?

A main-sequence star has a certain lifetime, t, because of thermonuclear "burning" of the hydrogen in the core of the star. How is this lifetime on the main sequence related to the mass M and luminosity L of the star? ( $\alpha$ means "proportional to")

When the stars of the following open clusters are plotted on an H-R diagram, the temperature values for the turning points are approximately: Coma (10,000 K), h + $\chi$ (40,000 K), M67 (7500 K), and Pleiades (20,000 K). Which cluster is oldest?

The ¹²C and ¹⁶O, which now form part of living matter, were part of the cold, dark nebula from which the Sun formed. How did they get there?

The H-R diagram for open star clusters (See Figure 19-15 of Universe, 11th ed.) shows the Sun at approximately the 10-billion-year mark on the main sequence. What is the meaning of this?

¹²C and ¹⁶O are among the most important elements in organic matter, including our bodies. What is the source of ¹²C and ¹⁶O in our solar system?

Suppose a Cepheid variable has been identified, and its period of brightness variability is measured to be 30 days. Its apparent magnitude is +23.3. How far away is it? (See Figure 19-21 of Universe, 11th ed.) Note: The Sun's apparent magnitude is -26.7.