Question 1

When the Sun entered the main sequence,its core was approximately 75% hydrogen and 25% helium,by mass.What was the ratio of hydrogen nuclei to helium nuclei?

Accepted Answer

A)   3:1
B)   4:1
C)   12:1
D)   16:1E) A) and B)
F) A) and C)

Question 2

What happens to a star after the start of helium nuclear reactions in its core compared with what it was like before these reactions began?

Accepted Answer

A)   The star is larger and hotter.
B)   The star is larger and cooler.
C)   The star is smaller and hotter.
D)   The star is smaller and cooler.E) A) and B)
F) None of the above

Question 3

On a Hertzsprung-Russell diagram describing the stars in a young cluster,in which position would you expect to find the T Tauri stars?

Accepted Answer

A)   well above the main sequence and to the left
B)   just above and slightly to the right of the main sequence
C)   well below the main sequence
D)   the upper right, well above the main sequenceE) A) and B)
F) B) and D)

Question 4

At what stage of evolution are the stars with similar luminosities between 50 and 100 times that of the Sun but spread over a range of temperatures?

Accepted Answer

A)   the main-sequence stage because the horizontal-branch region is part of the main sequence
B)   the pre-main-sequence stage, evolving toward the main sequence
C)   the white dwarf stage
D)   the post-main-sequence stageE) C) and D)
F) None of the above

Question 5

A protostar of about 1 solar mass is gradually contracting and becoming hotter.This activity causes its position in the Hertzsprung-Russell diagram to shift slowly:

Accepted Answer

A)   upward and toward the right.
B)   downward and toward the left.
C)   upward and toward the left.
D)   downward and toward the right.E) All of the above
F) None of the above

Question 6

Which stars are metal-rich?

Accepted Answer

A)   Population I stars
B)   very old stars
C)   Population II stars
D)   globular cluster starsE) A) and C)
F) All of the above

Question 7

What characteristic of Cepheid variables makes them extremely useful to astronomers?

Accepted Answer

A)   The absolute magnitude of Cepheid variables is related directly to their period of pulsation.
B)   The absolute magnitude of Cepheid variables is directly related to their diameter.
C)   The absolute magnitude of Cepheid variables is related directly to their metal content (heavy element abundance) .
D)   The absolute magnitude of Cepheid variables is related directly to their surface temperature.E) B) and D)
F) None of the above

Question 8

Which statement about the capability of an O-type star to trigger the formation of other stars is NOT correct?

Accepted Answer

A)   O-type stars are massive. When they form stellar nebulae, as the Sun did, small stars form instead of planets.
B)   The H II region surrounding an O-type star expands into the giant molecular cloud, producing a shock wave that can compress the un-ionized material and cause it to collapse.
C)   O-type stars are massive and thus have short lifetimes. After an O-type star erupts in a supernova, the material it ejects into space can eventually condense to form a new generation of stars.
D)   The shock wave produced when an O-type star forms a supernova can compress the ISM and cause it to collapse.E) A) and B)
F) B) and C)

Question 9

The Orion Nebula is a:

Accepted Answer

A)   spiral galaxy in the constellation Orion.
B)   red supergiant star.
C)   large interstellar gas and dust cloud containing young stars.
D)   supernova remnant, the material thrown out by an exploding star.E) A) and B)
F) A) and C)

Question 10

A degenerate-electron gas,which occurs in the core of a red giant star,lacks the "safety valve" of a normal gas because a rise in:

Accepted Answer

A)   pressure releases more electrons, thus increasing the pressure further.
B)   pressure reduces the number of electrons, causing the core to collapse.
C)   temperature does not change the pressure, so the gas does not expand and cool.
D)   temperature lowers the pressure, causing the star to contract.E) A) and D)
F) B) and C)

Question 11

Where are emission nebulae (H II regions) found?

Accepted Answer

A)   in or near old open clusters
B)   around hot stars
C)   in globular star clusters
D)   around low-mass starsE) C) and D)
F) B) and D)

Question 12

In comparing a young red giant star with the main-sequence star from which it evolved,which statement is NOT true?

Accepted Answer

A)   The core of the main-sequence star is hotter.
B)   Hydrogen fusion occurs in the core of the main-sequence star and in a shell around the core in the red giant star.
C)   The red giant star has a larger diameter.
D)   The red giant star has the cooler surface temperature.E) A) and C)
F) None of the above

Question 13

What major physical process is taking place inside stars that are on the main sequence in the Hertzsprung-Russell diagram?

Accepted Answer

A)   Hydrogen is being converted to helium in their cores.
B)   Hydrogen is being converted to helium in a shell around the helium-rich core.
C)   Helium is being converted to carbon in their cores.
D)   The gas is contracting gravitationally without nuclear reactions taking place.E) C) and D)
F) A) and C)

Question 14

After the helium flash in a low-mass star:

Accepted Answer

A)   all nuclear reactions cease.
B)   helium burning ceases in the core, but hydrogen burning continues in the layers around the core.
C)   helium burning begins in the core, and hydrogen burning ceases in the layers around the core.
D)   helium burning begins in the core, and hydrogen burning continues in the layers around the core.E) A) and B)
F) A) and C)

Question 15

If you were able to return to Earth 1 million years into the future,which view of the sky would be MOST likely?

Accepted Answer

A)   A few red stars would be missing since they would have evolved, but otherwise the stars would be the same and be in the same positions as they are today.
B)   Nearby stars would have moved in position, and no blue stars would be visible.
C)   Nearby stars would have moved in position and some stars that are presently blue would have changed color, but otherwise the sky would be very much as it is now since 1 million years is a very short time in astronomical terms.
D)   All the present stars, both blue and red, would be visible, but nearby stars would have moved in position.E) None of the above
F) B) and C)

Question 16

At what temperature do nuclear reactions begin in the core of a pre-main-sequence star?

Accepted Answer

A)   100 million K
B)   1 million K
C)   10 million K
D)   100,000 KE) C) and D)
F) None of the above

Question 17

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence.This cluster is:

Accepted Answer

A)   very young because the G and K stars are still evolving toward the main sequence.
B)   of indeterminate age since the age of the cluster cannot be estimated from the information given.
C)   impossible because cool stars cannot exist above the main sequence when hot stars are on the main sequence.
D)   old because the G and K stars are already evolving off (away from)  the main sequence.E) A) and D)
F) A) and C)

Question 18

The spectrum of stars in an open cluster is found to contain spectral lines from many heavy elements; the stars are known as "metal-rich." What is the source of these heavy elements?

Accepted Answer

A)   fusion reactions on the very hot surfaces of these stars
B)   The heavy-element content of these stars is not enhanced but the hydrogen and helium content has been depleted by intense stellar winds made up preferentially of these light elements.
C)   fusion reactions in the star cores, carried to the surface by convection
D)   the interstellar medium, which originated in explosions of stars earlier in history that had manufactured heavy elements by nuclear fusionE) None of the above
F) C) and D)

Question 19

The star zeta Pegasi (in the constellation Pegasus,the Flying Horse) has a spectral luminosity class of B8 V,which gives it a surface temperature of about 11,000 K.According to Table 11-2 of Comins,Discovering the Essential Universe,6th ed.,the expected main-sequence lifetime of zeta Pegasi is:

Accepted Answer

A)   much greater than 500 million years.
B)   about 500 million years.
C)   not defined by this information.
D)   about 500,000 years.E) None of the above
F) B) and C)

Question 20

Infrared stars in the Orion Nebula are examples of which stage of stellar evolution?

Accepted Answer

A)   red giant
B)   protostar and young star
C)   supernova remnants
D)   planetary nebulaE) B) and C)
F) A) and B)

Exam 11: The Lives of the Stars From Birth Through Middle Age

A protostar of about 1 solar mass is gradually contracting and becoming hotter.This activity causes its position in the Hertzsprung-Russell diagram to shift slowly:

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On a Hertzsprung-Russell diagram describing the stars in a young cluster,in which position would you expect to find the T Tauri stars?

Correct AnswerverifiedShow Answer

Which statement about the capability of an O-type star to trigger the formation of other stars is NOT correct?

Correct AnswerverifiedShow Answer

A degenerate-electron gas,which occurs in the core of a red giant star,lacks the "safety valve" of a normal gas because a rise in:

Correct AnswerverifiedShow Answer

If you were able to return to Earth 1 million years into the future,which view of the sky would be MOST likely?

Correct AnswerverifiedShow Answer

After the helium flash in a low-mass star:

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What characteristic of Cepheid variables makes them extremely useful to astronomers?

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Infrared stars in the Orion Nebula are examples of which stage of stellar evolution?

Correct AnswerverifiedShow Answer

The Orion Nebula is a:

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Where are emission nebulae (H II regions) found?

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The spectrum of stars in an open cluster is found to contain spectral lines from many heavy elements; the stars are known as "metal-rich." What is the source of these heavy elements?

Correct AnswerverifiedShow Answer

At what stage of evolution are the stars with similar luminosities between 50 and 100 times that of the Sun but spread over a range of temperatures?

Correct AnswerverifiedShow Answer

What happens to a star after the start of helium nuclear reactions in its core compared with what it was like before these reactions began?

Correct AnswerverifiedShow Answer

In comparing a young red giant star with the main-sequence star from which it evolved,which statement is NOT true?

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Which stars are metal-rich?

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At what temperature do nuclear reactions begin in the core of a pre-main-sequence star?

Correct AnswerverifiedShow Answer

When the Sun entered the main sequence,its core was approximately 75% hydrogen and 25% helium,by mass.What was the ratio of hydrogen nuclei to helium nuclei?

Correct AnswerverifiedShow Answer

What major physical process is taking place inside stars that are on the main sequence in the Hertzsprung-Russell diagram?

Correct AnswerverifiedShow Answer

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence.This cluster is:

Correct AnswerverifiedShow Answer

The star zeta Pegasi (in the constellation Pegasus,the Flying Horse) has a spectral luminosity class of B8 V,which gives it a surface temperature of about 11,000 K.According to Table 11-2 of Comins,Discovering the Essential Universe,6th ed.,the expected main-sequence lifetime of zeta Pegasi is:

Correct AnswerverifiedShow Answer

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