Question 1

How much smaller (in radius)  than the Sun is a white dwarf star whose temperature is the same as that of the Sun? (See Figure 17-15b.(in the text) )

Accepted Answer

A)  100 times smaller
B)  It will be the same size as the Sun, because it has the same temperature.
C)  10 times smaller
D)  2 times smallerE) B) and D)
F) A) and B)

Question 2

On the basis of the graph of absorption line strengths (in Figure 17-12) , what is the spectral type of a star with the following spectral pattern: very strong He I lines, moderately strong H lines, weak Si III lines, and no Ca II, Fe II, or He II lines?

Accepted Answer

A)  M
B)  F
C)  B
D)  AE) All of the above
F) A) and B)

Question 3

An eclipsing binary system is:

Accepted Answer

A)  two stars detected as such by movement of lines in their spectra by varying Doppler shifts.
B)  two stars that periodically eclipse each other.
C)  two stars clearly separated when viewed from Earth.
D)  a star that is periodically eclipsed by the Moon.E) None of the above
F) All of the above

Question 4

What is the intensity of sunlight per square meter reaching Saturn compared to the intensity at Earth's orbital distance?

Accepted Answer

A)  1/91
B)  91 times brighter
C)  1/9.5
D)  1/3.1E) A) and D)
F) All of the above

Question 5

Using Figure 17-15, determine which of the following is the correct sequence of stars in order of increasing size or stellar radius.

Accepted Answer

A)  Mira, Betelguese, the Sun, and Sirius B
B)  Betelguese, Mira, the Sun, and Sirius B
C)  Sirius B, the Sun, Betelguese, and Mira
D)  Sirius B, the Sun, Mira, and BetelgueseE) All of the above
F) B) and D)

Question 6

The star Hadar has a spectral classification of B1 III. This tells us that Hadar is a:

Accepted Answer

A)  hot supergiant.
B)  cool giant.
C)  hot giant.
D)  cool supergiant.E) B) and D)
F) B) and C)

Question 7

Using the Hertzsprung-Russell diagram in Figure 17-15a and the mass-luminosity relationship for main-sequence stars shown in Figure 17-22, which of the following is the correct sequence of stars in increasing order of mass?

Accepted Answer

A)  Barnard's Star, Altair, the Sun, and Regulus
B)  Regulus, Barnard's Star, the Sun, and Altair
C)  Regulus, Altair, the Sun, and Barnard's Star
D)  Barnard's Star, the Sun, Altair, and RegulusE) None of the above
F) C) and D)

Question 8

What fraction of the stars in the night sky are main-sequence stars?

Accepted Answer

A)  almost none of them, less than 1%
B)  relatively few of them, about 20%
C)  almost all of them, about 90%
D)  roughly half of them, about 55%E) All of the above
F) C) and D)

Question 9

Two stars that differ from each other by five magnitudes have a ratio of brightness of:

Accepted Answer

A)  5.
B)  25.
C)  10.
D)  100.E) A) and B)
F) A) and C)

Question 10

How do two stars in a binary system orbit each other? (See Figure 17-21.(in the text) )

Accepted Answer

A)  They both follow elliptical orbits around a common point between the stars.
B)  The lower mass star orbits in an ellipse around the center of the larger mass star.
C)  The larger mass star orbits around the center of the smaller mass star.
D)  They both move on the same elliptical orbit around one of its foci.E) None of the above
F) A) and B)

Question 11

Brown dwarfs give out energy due mainly to:

Accepted Answer

A)  nuclear fusion reactions.
B)  the Kelvin-Holmholtz contraction.
C)  radioactivity.
D)  nuclear fission reactions.E) A) and B)
F) C) and D)

Question 12

The radius of a typical supergiant is how many times the radius of a typical white dwarf?

Accepted Answer

A)  10
B)  103
C)  105
D)  107E) B) and C)
F) A) and B)

Question 13

The star β Arietis has an apparent magnitude of +2.7 and a distance of 52 ly. What is its absolute magnitude, M?

Accepted Answer

A)  +6.2
B)  -0.9
C)  +1.7
D)  +3.7E) A) and D)
F) C) and D)

Question 14

A particular star has 12 times the radius of the Sun and only 60% of the Sun's surface temperature. What is the star's luminosity in solar units (  L⊙L_{\odot}L⊙​  ) ? (See Box 17-4.)

Accepted Answer

A)  51.8  L⊙L_{\odot}L⊙​ 
B)  18.7  L⊙L_{\odot}L⊙​ 
C)  22.6  L⊙L_{\odot}L⊙​ 
D)  7.2  L⊙L_{\odot}L⊙​E) A) and D)
F) A) and C)

Question 15

The total apparent motion against the background sky as a result of Earth's motion halfway around its orbit of a star whose distance from the Sun is 40 pc is:

Accepted Answer

A)  0.0125 radian or 0.72°.
B)  0.0125 arcmin.
C)  0.0125 arcsec.
D)  40 arcsec.E) A) and B)
F) B) and C)

Question 16

The speed of a star in km/s, measured in a direction perpendicular to the line of sight from Earth to the star, is known as:

Accepted Answer

A)  tangential velocity.
B)  proper motion.
C)  radial velocity.
D)  retrograde motion.E) None of the above
F) A) and D)

Question 17

Why is it that stars with low surface temperature, much cooler than 10,000 K, show very weak or no hydrogen Balmer lines in absorption?

Accepted Answer

A)  To absorb at Balmer wavelengths, atoms need to have electrons in the n = 2 level, and electrons will not be excited to this level by collisions at these low temperatures.
B)  The stellar gas is so cool that there is no radiation to be absorbed at the wavelength of Balmer lines.
C)  Hydrogen atoms have to be hot enough to be ionized to show Balmer absorption.
D)  Hydrogen atoms will have no electrons at any energy level at these low temperatures.E) A) and D)
F) A) and C)

Question 18

The star Procyon has a parallax of 0.287 arcsec and a proper motion of 1.25 arcsec per year. What is the tangential velocity of Procyon?

Accepted Answer

A)  68 km/s
B)  21 km/s
C)  1.7 km/s
D)  16 km/sE) B) and D)
F) All of the above

Question 19

The apparent angular movement of a nearby star against the background stars as a consequence of its motion in space is known as:

Accepted Answer

A)  radial velocity.
B)  tangential velocity.
C)  proper motion.
D)  retrograde motion.E) A) and B)
F) None of the above

Question 20

If Mercury is at 0.4 au, the Moon is at 1.0 au, and the inverse-square law holds, how much more light falls on a unit area of Mercury's surface than on an equivalent area of the Moon?

Accepted Answer

A)  6.25 times more
B)  0.4 times as much
C)  2.5 times more
D)  16 times moreE) B) and D)
F) B) and C)

Exam 17: The Nature of the Stars

The star Hadar has a spectral classification of B1 III. This tells us that Hadar is a:

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Using the Hertzsprung-Russell diagram in Figure 17-15a and the mass-luminosity relationship for main-sequence stars shown in Figure 17-22, which of the following is the correct sequence of stars in increasing order of mass?

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What fraction of the stars in the night sky are main-sequence stars?

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The apparent angular movement of a nearby star against the background stars as a consequence of its motion in space is known as:

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A particular star has 12 times the radius of the Sun and only 60% of the Sun's surface temperature. What is the star's luminosity in solar units ( L⊙L_{\odot}L⊙​ ) ? (See Box 17-4.)

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On the basis of the graph of absorption line strengths (in Figure 17-12) , what is the spectral type of a star with the following spectral pattern: very strong He I lines, moderately strong H lines, weak Si III lines, and no Ca II, Fe II, or He II lines?

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The star β Arietis has an apparent magnitude of +2.7 and a distance of 52 ly. What is its absolute magnitude, M?

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The total apparent motion against the background sky as a result of Earth's motion halfway around its orbit of a star whose distance from the Sun is 40 pc is:

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The speed of a star in km/s, measured in a direction perpendicular to the line of sight from Earth to the star, is known as:

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The star Procyon has a parallax of 0.287 arcsec and a proper motion of 1.25 arcsec per year. What is the tangential velocity of Procyon?

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How do two stars in a binary system orbit each other? (See Figure 17-21.(in the text) )

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How much smaller (in radius) than the Sun is a white dwarf star whose temperature is the same as that of the Sun? (See Figure 17-15b.(in the text) )

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If Mercury is at 0.4 au, the Moon is at 1.0 au, and the inverse-square law holds, how much more light falls on a unit area of Mercury's surface than on an equivalent area of the Moon?

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Why is it that stars with low surface temperature, much cooler than 10,000 K, show very weak or no hydrogen Balmer lines in absorption?

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Brown dwarfs give out energy due mainly to:

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The radius of a typical supergiant is how many times the radius of a typical white dwarf?

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What is the intensity of sunlight per square meter reaching Saturn compared to the intensity at Earth's orbital distance?

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Two stars that differ from each other by five magnitudes have a ratio of brightness of:

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Using Figure 17-15, determine which of the following is the correct sequence of stars in order of increasing size or stellar radius.

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An eclipsing binary system is:

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A particular star has 12 times the radius of the Sun and only 60% of the Sun's surface temperature. What is the star's luminosity in solar units ( $L_{\odot}$ ) ? (See Box 17-4.)

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