Question 1

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

Accepted Answer

Globular clusters are composed of old stars with little to no gas or dust, as these elements have been used up in the formation of the stars.

Question 2

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

Accepted Answer

Globular clusters do contain main-sequence stars, along with other types of stars such as red giants and white dwarfs.

Question 3

An astronomer studying a globular cluster plots its stars on a Hertzsprung-Russell diagram and finds that certain stars in the cluster lie on the horizontal branch. What does this astronomer immediately know about these stars?
A)They are still contracting toward the main sequence.
B)They are burning hydrogen into helium in their cores.
C)They are burning helium into carbon and oxygen in their cores.
D)They are burning helium into carbon and oxygen in a shell around their cores.

Accepted Answer

Stars on the horizontal branch of the Hertzsprung-Russell diagram are in a phase where they are burning helium into carbon and oxygen in their cores.

Question 4

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

Accepted Answer

The "turnoff" point in a star cluster's H-R diagram is where the highest-mass main-sequence stars have exhausted their hydrogen fuel and are leaving the main sequence. This point helps determine the cluster's age.

Question 5

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.) ​
 ​
A)100 million years
B)1 billion years
C)500 million years
D)4 billion years

Accepted Answer

The answer of Suppose that, when the stars in a...

Question 6

The stars at the turnoff point in the H-R diagram of the Hyades star cluster have an absolute magnitude of approximately M = +2, whereas those at the turnoff point in the cluster M41 have M = 0. From this information, we can say with certainty that the Hyades cluster:
A)is farther away than M41.
B)older than M41.
C)has more stars in it than M41.
D)younger than M41.

Accepted Answer

The turnoff point in an H-R diagram indicates the brightest, hottest, and most massive stars that have exhausted their core hydrogen fuel and are beginning to evolve off the main sequence. The higher the absolute magnitude of the stars at the turnoff point, the younger the cluster. Therefore, since the Hyades stars have a lower absolute magnitude at the turnoff point than those in cluster M41, the Hyades are older than M41. The distance and number of stars in the clusters cannot be determined from this information.

Question 7

Suppose you pick 100 stars at random from the night sky and plot the apparent magnitude versus color ratio for these stars. What would this plot show you?
A)This is a color-magnitude diagram. By noting the turnoff point on the main sequence you could determine the age of the oldest star in the group.
B)Because we are not examining stars in a cluster, there will be no turnoff point. But you will have an H-R diagram with main sequence, giants, and white dwarves.
C)Because we are not examining stars in a cluster, there will be no turnoff point. It will be an H-R diagram, but with only 100 stars it is unlikely that more than one or two stars will be red giants.
D)Because we are plotting apparent magnitude versus color ratio for a group of unrelated stars, the plot will probably not show any particular pattern.

Accepted Answer

Since the stars are randomly picked from the night sky and are not a part of any cluster or group, there is no relation between them. Hence, the plot will not show any particular pattern.

Question 8

When the stars of the following open clusters are plotted on an H-R diagram, the luminosity values for the turning points are approximately (in solar luminosities): Coma (7), h + $\chi$ (600), M67 (2), and Pleiades (70). Which cluster is youngest?
A)Coma
B)h + $\chi$
C)M67
D)Pleiades

Accepted Answer

The H-R diagram turning point luminosity is higher for younger clusters because they have more massive stars that have not yet evolved off the main sequence. h + $\chi$ with a turning point of 600 solar luminosities indicates it has the most massive (and thus youngest) stars among the options.

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

Accepted Answer

The main sequence turnoff point on an H-R diagram is a good indicator of the age of a star cluster. The cooler the turnoff point, the older the cluster. M67 has the lowest temperature turnoff point, indicating that it is the oldest cluster.

Question 10

When the stars of the following open clusters are plotted on an H-R diagram, the absolute magnitude values for the turning points are approximately: Coma (2.4), h + $\chi$ (-2), M67 (4.5), and Pleiades (0.3). Which cluster is youngest?
A)Coma
B)h + $\chi$
C)M67
D)Pleiades

Accepted Answer

The youngest star clusters have the brightest turnoff points on the H-R diagram because their most massive stars have not yet evolved off the main sequence. The h + $\chi$ cluster, with a turnoff point at an absolute magnitude of -2, indicates it has the most massive (and thus youngest) stars still on the main sequence.

Question 11

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?
​
 ​
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.

Accepted Answer

The H-R diagram for open star clusters shows the position of stars of different ages and evolutionary stages. The fact that the Sun is located at approximately the 10-billion-year mark on the main sequence means that it is a middle-aged star, halfway through its main sequence lifetime. Since stars evolve slowly along the main sequence, the Sun will not change its position very much on the diagram during the rest of its main sequence lifetime. Therefore, it will still be near the 10-billion-year mark when it finishes its hydrogen burning.

Question 12

Where on the H-R diagram would you expect to find Population I and II stars?
A)Each population should be scattered throughout the entire diagram.
B)Population I stars are restricted to the left (high temperature) side of the diagram, and Population II stars are to the right side.
C)Population I stars are restricted to the right (low temperature) side of the diagram, and Population II stars are to the left side.
D)Population I stars are represented across the entire H-R diagram, but Population II stars exist primarily on the right side.

Accepted Answer

Population I stars, which are younger and metal-rich, can be found throughout the H-R diagram, including the main sequence, giants, and supergiants. Population II stars, which are older and metal-poor, are primarily found in the cooler, less luminous regions, such as the red giant branch.

Question 13

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)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.

Accepted Answer

Sulfur (¹²C) and Oxygen (¹⁶O) are among the most common elements in the Solar System and all known life forms. They are believed to have originated from the cold, dark nebula from which the Sun and the rest of the Solar System condensed. These elements were present in the original solar nebula and were incorporated into the bodies that formed in it.

Question 14

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? 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.

Accepted Answer

Carbon and oxygen are formed in the red giant phase of stars through nuclear fusion processes.

Question 15

Population I stars are metal rich. Where did these metals come from?
A)They formed in the Big Bang.
B)They originated in the earlier generation of Population II stars, especially the least massive of these.
C)They originated in the earlier generation of Population II stars, especially the most massive of these.
D)They were created by nuclear fusion within the Population I stars themselves.

Accepted Answer

Population II stars are the oldest stars, and they are metal-poor because they formed before the universe had a chance to create heavier elements through nuclear fusion. As Population II stars became more massive, they exploded as supernovae, creating heavy elements such as iron, nickel, and gold. These elements were then incorporated into the next generation of stars, known as Population I stars, which formed from the enriched gas and dust of the previous generation. Therefore, Population I stars are metal-rich because they formed from the remnants of earlier Population II stars, especially the most massive ones.

Question 16

Mira variables are not as useful as other variable stars in making astronomical calculations because:
A)their periods are not always regular.
B)their periods are too long to be measured easily.
C)there are relatively few of them.
D)no Mira variables are close enough for a parallax measurement.

Accepted Answer

Mira variables have irregular periods, which makes them less useful in making astronomical calculations compared to other variable stars with more regular periods.

Question 17

A Cepheid variable pulsates because compressing a component in its atmosphere causes this component to ionize and become opaque, thus trapping heat that later causes the star to expand. This atmospheric component is:
A)hydrogen.
B)helium.
C)carbon.
D)oxygen.

Accepted Answer

Cepheid variables pulsate due to the ionization of helium in their atmospheres. When helium is ionized, it becomes opaque, trapping heat and causing the star to expand.

Question 18

When a Cepheid variable star reaches maximum luminosity, which other property of the star does NOT also reach a maximum?
A)surface temperature
B)diameter
C)outward radial velocity
D)luminosity

Accepted Answer

When a Cepheid variable star reaches maximum luminosity, its diameter does not also reach a maximum. Instead, the diameter decreases as the outer layers of the star are pushed outward by the pulsations, causing them to cool and become less luminous. This is known as the "radius-luminosity" relationship and is used to determine the distance to Cepheid variable stars.

Question 19

RR Lyrae variables are likely to be found in:
A)very young clusters, where high-mass stars are undergoing core hydrogen burning.
B)giant molecular clouds, where protostars are forming from gas and dust clouds.
C)young-to-intermediate-age clusters, where high-mass stars are undergoing central helium burning.
D)globular clusters, where low-mass stars are undergoing core helium burning.

Accepted Answer

RR Lyrae variables are often found in globular clusters, which are known to contain low-mass stars that are undergoing core helium burning.

Question 20

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

Accepted Answer

The answer of Suppose a Cepheid variable has been identified,...

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

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

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

An astronomer studying a globular cluster plots its stars on a Hertzsprung-Russell diagram and finds that certain stars in the cluster lie on the horizontal branch. What does this astronomer immediately know about these stars?

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

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.)

The stars at the turnoff point in the H-R diagram of the Hyades star cluster have an absolute magnitude of approximately M = +2, whereas those at the turnoff point in the cluster M41 have M = 0. From this information, we can say with certainty that the Hyades cluster:

Suppose you pick 100 stars at random from the night sky and plot the apparent magnitude versus color ratio for these stars. What would this plot show you?

When the stars of the following open clusters are plotted on an H-R diagram, the luminosity values for the turning points are approximately (in solar luminosities) : Coma (7) , h + $\chi$ (600) , M67 (2) , and Pleiades (70) . Which cluster is youngest?

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?

When the stars of the following open clusters are plotted on an H-R diagram, the absolute magnitude values for the turning points are approximately: Coma (2.4) , h + $\chi$ (-2) , M67 (4.5) , and Pleiades (0.3) . Which cluster is youngest?

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?

Where on the H-R diagram would you expect to find Population I and II stars?

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?

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?

Population I stars are metal rich. Where did these metals come from?

Mira variables are not as useful as other variable stars in making astronomical calculations because:

A Cepheid variable pulsates because compressing a component in its atmosphere causes this component to ionize and become opaque, thus trapping heat that later causes the star to expand. This atmospheric component is:

When a Cepheid variable star reaches maximum luminosity, which other property of the star does NOT also reach a maximum?

RR Lyrae variables are likely to be found in:

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.

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

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

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

An astronomer studying a globular cluster plots its stars on a Hertzsprung-Russell diagram and finds that certain stars in the cluster lie on the horizontal branch. What does this astronomer immediately know about these stars?

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

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.) ​ ​

The stars at the turnoff point in the H-R diagram of the Hyades star cluster have an absolute magnitude of approximately M = +2, whereas those at the turnoff point in the cluster M41 have M = 0. From this information, we can say with certainty that the Hyades cluster:

Suppose you pick 100 stars at random from the night sky and plot the apparent magnitude versus color ratio for these stars. What would this plot show you?

When the stars of the following open clusters are plotted on an H-R diagram, the luminosity values for the turning points are approximately (in solar luminosities) : Coma (7) , h + χ\chiχ (600) , M67 (2) , and Pleiades (70) . Which cluster is youngest?

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?

When the stars of the following open clusters are plotted on an H-R diagram, the absolute magnitude values for the turning points are approximately: Coma (2.4) , h + χ\chiχ (-2) , M67 (4.5) , and Pleiades (0.3) . Which cluster is youngest?

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? ​ ​

Where on the H-R diagram would you expect to find Population I and II stars?

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?

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?

Population I stars are metal rich. Where did these metals come from?

Mira variables are not as useful as other variable stars in making astronomical calculations because:

A Cepheid variable pulsates because compressing a component in its atmosphere causes this component to ionize and become opaque, thus trapping heat that later causes the star to expand. This atmospheric component is:

When a Cepheid variable star reaches maximum luminosity, which other property of the star does NOT also reach a maximum?

RR Lyrae variables are likely to be found in:

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. ​ ​

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.)

When the stars of the following open clusters are plotted on an H-R diagram, the luminosity values for the turning points are approximately (in solar luminosities) : Coma (7) , h + $\chi$ (600) , M67 (2) , and Pleiades (70) . Which cluster is youngest?

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?

When the stars of the following open clusters are plotted on an H-R diagram, the absolute magnitude values for the turning points are approximately: Coma (2.4) , h + $\chi$ (-2) , M67 (4.5) , and Pleiades (0.3) . Which cluster is youngest?

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?

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?

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.