Question 1

In a particular binary star system,only one star is visible because the other star is too faint to see at that distance.An astronomer measures the size (semimajor axis) and period of the orbit of the visible star.From this information,the astronomer:

Accepted Answer

A)   cannot calculate anything about the mass-both stars have to be visible to do so.
B)   can calculate the mass of each star.
C)   can calculate the sum of the masses of the two stars but not the mass of each star separately.
D)   can calculate the mass of the visible star but not that of the unseen star.E) None of the above
F) All of the above

Question 2

The light intensity from a particular star remains essentially constant,except for short and regular decreases and increases by a fixed amount.What is the explanation for this phenomenon?

Accepted Answer

A)   One star is regularly eclipsing its companion as they move in mutual orbits whose plane is close to the line of sight.
B)   A variable star is pulsating in size, temperature, and intensity.
C)   A massive, dark planet is periodically passing in front of the star's visible surface.
D)   Shells of absorbing gas and dust are being periodically ejected from the star's surface and are subsequently dispersing into space.E) A) and D)
F) B) and D)

Question 3

The spectrum of a very distant star shows spectral absorption lines of ionized helium,He II,and molecular absorption bands from titanium oxide,TiO.What could you conclude about this star?

Accepted Answer

A)   The star is probably the spectrum of a binary system, two stars close together, a hot star and a cooler companion, unresolved as separate stars from Earth but contributing separate spectra.
B)   The star must have a very hot atmosphere containing helium gas overlying a much cooler stellar surface.
C)   The star must have a thick, cool atmosphere overlying a hot stellar atmosphere.
D)   There must be cool, interstellar gas containing TiO between the star and Earth.E) B) and D)
F) All of the above

Question 4

You are observing a binary system with two stars of masses M₁ and M₂.You determine a,the semimajor axis (also the average distance between the stars) and P,the period of their motion.Using this information in Kepler's third law,you can calculate:

Accepted Answer

A)   M₁ or M₂ but not both.
B)   M₁/M₂.
C)   M₁ + M₂.
D)   both M₁ and M₂.E) A) and B)
F) All of the above

Question 5

Looking at the clock face on a distant steeple,the clock subtends an angle of 275 arcseconds.How far away is it?

Accepted Answer

A)   275 feet
B)   275 meters
C)   1/275 km
D)   The distance cannot be computed from the given information.E) B) and D)
F) C) and D)

Question 6

Where are the MOST massive stars to be found in the main sequence of a Hertzsprung-Russell diagram?

Accepted Answer

A)   the upper left end
B)   Main-sequence stars all have approximately the same mass, by definition.
C)   the center
D)   the lower right endE) None of the above
F) All of the above

Question 7

Which atom or ion produces the strongest absorption lines in the spectra of stars with the highest surface temperatures?

Accepted Answer

A)   He II, ionized helium
B)   Fe I, neutral iron
C)   Ca II, singly ionized calcium
D)   H I, neutral hydrogenE) C) and D)
F) A) and B)

Question 8

The Hertzsprung-Russell diagram is a plot of:

Accepted Answer

A)   apparent brightness against intrinsic brightness of a group of stars.
B)   apparent brightness against distance for stars near the Sun.
C)   luminosity against mass of a group of stars.
D)   absolute magnitude (or intrinsic brightness)  against temperature of a group of stars.E) A) and B)
F) A) and C)

Question 9

The luminosity of a star is:

Accepted Answer

A)   its brightness as seen by people on Earth.
B)   its brightness if it were at a distance of 10 pc (32.6 ly)  from Earth.
C)   its total energy output into all space.
D)   another name for its color or surface temperature.E) B) and C)
F) A) and B)

Question 10

Parallax of a nearby star is used to estimate its:

Accepted Answer

A)   surface temperature.
B)   distance from Earth.
C)   apparent magnitude.
D)   physical size or diameter.E) A) and B)
F) C) and D)

Question 11

Two stars,one classified A4 V and the other F8 V,have the same apparent magnitude.There is no significant amount of absorption of starlight by interstellar material.From this information we know that the A4 V star is _____ the F8 V star.

Accepted Answer

A)   farther from the Sun than
B)   at the same distance from the Sun as
C)   smaller than
D)   closer to the Sun thanE) A) and B)
F) A) and C)

Question 12

A star of apparent magnitude +5 appears _____ than a star of apparent magnitude +3.

Accepted Answer

A)   fainter
B)   farther away
C)   brighter
D)   either brighter or fainter, depending on the distance to the stars,E) All of the above
F) B) and C)

Question 13

Two stars are found to have the same luminosity.However,one star has twice the surface temperature of the other.From this information,what can you determine about their radii?

Accepted Answer

A)   The hotter star has half the radius of the cooler star.
B)   The cooler star has half the radius of the hotter star.
C)   The hotter star has a quarter the radius of the cooler star.
D)   Nothing can be determined about the radii from this information.E) B) and D)
F) All of the above

Question 14

The Sun's spectrum peaks in the green region (i.e.,green is the most intense color in its spectrum) .The spectrum of Rigel (the knee of Orion) peaks in the short-wavelength end of the visible spectrum.Compared with the Sun,Rigel is:

Accepted Answer

A)   cooler and redder.
B)   hotter and redder.
C)   cooler and whiter.
D)   hotter and whiter.E) None of the above
F) C) and D)

Question 15

The ancient Greek astronomer Hipparchus introduced the magnitude scale on which he called the brightest stars first magnitude.Today,the brightest star in the night sky is Sirius,with a magnitude of -1.4,considerably brighter than first magnitude.Why the discrepancy?

Accepted Answer

A)   Sirius was formed since the era in which Hipparchus lived.
B)   Sirius existed during Hipparchus's lifetime, but it has obviously brightened considerably since then.
C)   Hipparchus had poor eyesight and made many classification errors.
D)   After using modern scientific instruments to measure the actual energy output of stars, astronomers modified the magnitude scale of Hipparchus.E) C) and D)
F) A) and D)

Question 16

The star Arcturus is classified as K2 III,which means that it is a:

Accepted Answer

A)   hot giant.
B)   cool supergiant.
C)   cool giant.
D)   cool main-sequence star.E) C) and D)
F) B) and C)

Question 17

Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again.Explain.

Accepted Answer

A)   The effect of the gravitational field of one star on the atoms of the second star periodically produces spectral line shifts.
B)   The magnetic field of one star produces Zeeman periodic splitting of spectral lines in atoms of the second star.
C)   Oscillations on the surfaces of the stars lead to Doppler-shifted lines.
D)   Motion toward and away from Earth during their orbital motion results in Doppler shift of light from these stars at times and no shift when the stars are moving perpendicular to the line of sight.E) A) and C)
F) All of the above

Question 18

Which important stellar parameter can be derived from the study of binary stars mutually bound to each other by gravitational forces?

Accepted Answer

A)   stellar masses
B)   distance of the stars from Earth
C)   age of the stars
D)   surface temperature of the starsE) B) and C)
F) A) and B)

Question 19

Which sentence describes the relationship between mass and luminosity of stars on the main sequence?

Accepted Answer

A)   The luminosity of stars increases with mass up to a peak around 1 solar mass, then decreases as the mass continues to increase.
B)   Luminosity is independent of the stellar mass.
C)   The larger the stellar mass, the larger is the luminosity.
D)   The greater the stellar mass, the less is the luminosity.E) A) and C)
F) B) and C)

Question 20

The star ɛ Canis Majoris has an absolute magnitude of -4.1 and a spectral class of B2.Using Figures 10-7 and 10-8 of Comins,Discovering the Essential Universe,6th ed.,how would Canis Majoris be classified?

Accepted Answer

A)   B-type white dwarf
B)   B2 III
C)   B2 V
D)   B2 IE) C) and D)
F) None of the above

Exam 10: Characterizing Stars

Two stars,one classified A4 V and the other F8 V,have the same apparent magnitude.There is no significant amount of absorption of starlight by interstellar material.From this information we know that the A4 V star is _____ the F8 V star.

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A star of apparent magnitude +5 appears _____ than a star of apparent magnitude +3.

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The light intensity from a particular star remains essentially constant,except for short and regular decreases and increases by a fixed amount.What is the explanation for this phenomenon?

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The Sun's spectrum peaks in the green region (i.e.,green is the most intense color in its spectrum) .The spectrum of Rigel (the knee of Orion) peaks in the short-wavelength end of the visible spectrum.Compared with the Sun,Rigel is:

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You are observing a binary system with two stars of masses M₁ and M₂.You determine a,the semimajor axis (also the average distance between the stars) and P,the period of their motion.Using this information in Kepler's third law,you can calculate:

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Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again.Explain.

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The star ɛ Canis Majoris has an absolute magnitude of -4.1 and a spectral class of B2.Using Figures 10-7 and 10-8 of Comins,Discovering the Essential Universe,6th ed.,how would Canis Majoris be classified?

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The Hertzsprung-Russell diagram is a plot of:

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Where are the MOST massive stars to be found in the main sequence of a Hertzsprung-Russell diagram?

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Which sentence describes the relationship between mass and luminosity of stars on the main sequence?

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The star Arcturus is classified as K2 III,which means that it is a:

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Two stars are found to have the same luminosity.However,one star has twice the surface temperature of the other.From this information,what can you determine about their radii?

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The ancient Greek astronomer Hipparchus introduced the magnitude scale on which he called the brightest stars first magnitude.Today,the brightest star in the night sky is Sirius,with a magnitude of -1.4,considerably brighter than first magnitude.Why the discrepancy?

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In a particular binary star system,only one star is visible because the other star is too faint to see at that distance.An astronomer measures the size (semimajor axis) and period of the orbit of the visible star.From this information,the astronomer:

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The spectrum of a very distant star shows spectral absorption lines of ionized helium,He II,and molecular absorption bands from titanium oxide,TiO.What could you conclude about this star?

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Looking at the clock face on a distant steeple,the clock subtends an angle of 275 arcseconds.How far away is it?

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Which atom or ion produces the strongest absorption lines in the spectra of stars with the highest surface temperatures?

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Which important stellar parameter can be derived from the study of binary stars mutually bound to each other by gravitational forces?

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Parallax of a nearby star is used to estimate its:

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The luminosity of a star is:

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