Deck 11: Measuring the Stars: the Main Sequence and Its Meaning

Question 1

Which of the following combinations of measurements CANNOT be used to determine a star's radius?

A) brightness and peak wavelength
B) angular size and distance
C) brightness, distance, and temperature
D) luminosity and peak wavelength

Answer 1

brightness and peak wavelength

Question 2

What property of a star's spectral lines allows astronomers to measure stellar masses?

A) depth
B) width
C) wavelength
D) spacing

Answer 2

width

Question 3

Why are stars considered to be thermodynamic systems?

A) Stars are hot.
B) Stars are always in motion.
C) Stars are giant collections of atoms.
D) Stars are powered by combustion.

Answer 3

Stars are giant collections of atoms.

Question 4

What property of a star can best be used to determine its temperature?

A) luminosity
B) color
C) brightness
D) velocity

Question 5

Star A's spectrum is most intense at 500 nm,while star B's spectrum is most intense at 750 nm.If star A has a temperature of 5,800 K,what is the temperature of star B?

A) 13,000 K
B) 8,700 K
C) 4,500 K
D) 3,850 K

Question 6

How would astronomers measure the velocity of the star shown in the figure below?

A) through its spectrum
B) through a transit
C) through its angular velocity across the sky
D) through its brightening or dimming with time

Question 7

If star A has an apparent magnitude of 8 while star B has an apparent magnitude of 13,then star A is ________ than star B.

A) 100 times fainter
B) 5 times fainter
C) 5 times brighter
D) 100 times brighter

Question 8

What properties of Cepheid variable stars are most often measured to determine their distance?

A) luminosity and brightness
B) period and brightness
C) luminosity and temperature
D) period and temperature

Question 9

How have astronomers learned about the life cycles of stars?

A) through laboratory experiments
B) by studying the Big Bang
C) by studying the complete life cycles of individual stars
D) by measuring the properties of many stars at a single instant

Question 10

What was Henrietta Leavitt's most important contribution to astronomy?

A) the spectral typing of stars
B) the relationship of stellar spectral type to temperature
C) the period-luminosity relation of Cepheid variables
D) the discovery of interstellar reddening

Question 11

Two stars orbit each other on circular orbits.The star with the larger orbital radius has a:

A) larger orbital period.
B) smaller mass.
C) smaller orbital speed.
D) smaller orbital period.

Question 12

A star has a parallax of 0.05 arcseconds.How far away from Earth is the star?

A) 20 parsecs
B) 5 parsecs
C) 0.5 parsecs
D) 0.05 parsecs

Question 13

What property of a star's spectral lines allows astronomers to measure stellar masses?

A) redshift
B) width
C) variability
D) depth

Question 14

Star A has an apparent magnitude of 7,while star B has an apparent magnitude of 12.If star A is four times more luminous than star B,how do the distances of the two stars compare?

A) Star A is 25 times farther than star B.
B) Star A is 5 times farther than star B.
C) Star A is 25 times closer than star B.
D) Star A is 5 times closer than star B.

Question 15

What quantities must be measured in order to calculate the luminosity of a star?

A) brightness and radius
B) radius and distance
C) temperature and distance
D) brightness and distance

Question 16

Which of the following must be measured in order to determine a star's proper motion?

A) angular position at multiple times
B) mass
C) redshift or blueshift
D) radius

Question 17

Stars A and B have equal brightness,but star B is eight times as far from Earth as star A.How much more luminous is star A than star B?

A) 1/64
B) 1/8
C) 8
D) 64

Question 18

Two stars orbit their common center of mass on circular orbits.Star A is four times more massive than star B.How do their orbital periods compare to each other?

A) Star A has a longer orbital period than star B.
B) Star B has a longer orbital period than star A.
C) They are the same.
D) The orbital periods cannot be determined without knowing their initial velocities.

Question 19

The Hubble Space Telescope has detected galaxies with apparent magnitudes of about 30.Approximately how much fainter are these galaxies than stars with an apparent magnitude of 5?

A) 10²⁵ times
B) 10¹⁰ times
C) 2,500 times
D) 25 times

Question 20

Which of the following is a relational property of stars?

A) radius
B) temperature
C) luminosity
D) distance

Question 21

On the main sequence,a star's spectral type is ultimately determined by its:

A) distance.
B) luminosity.
C) composition.
D) mass.

Question 22

Which of the following correctly orders the spectral types of stars from coolest to hottest?

A) OMKGFBA
B) MKGFABO
C) ABFGKMO
D) OBAFGKM

Question 23

The figure below shows the apparent position of star A on the sky at two different positions in Earth's orbit.How far away is the star?

A) 0.1 parsec
B) 1 parsec
C) 10 parsecs
D) 100 parsecs

Question 24

If the Sun spends 10 billion years on the main sequence,how long will a star 100 times more massive than the Sun spend there?

A) 10⁵ years
B) 3 × 10⁶ years
C) 10⁹ years
D) 10¹¹ years

Question 25

The figure below shows an HR diagram.What is the name for the feature marked "X"?

A) asymptotic giant branch
B) T Tauri track
C) main sequence
D) red giant branch

Question 26

What determines the location of a star on the main sequence?

A) age
B) mass
C) composition
D) the star's principal fusion reaction

Question 27

On an HR diagram,the star Mira appears directly below the star Betelgeuse.Compared to Betelgeuse,Mira has a:

A) lower surface temperature.
B) higher surface temperature.
C) larger radius.
D) smaller radius.

Question 28

Which of the following stellar properties does NOT increase as you trace the main sequence from right to left on an HR diagram?

A) fusion rate
B) peak wavelength
C) surface area
D) temperature

Question 29

The figure below shows a binary star system.Which of the following correctly characterizes the spectrum of this system at the instant shown in the figure?

A) Star A's spectral lines have a smaller blueshift, while star B's spectral lines have a larger redshift.
B) Star A's spectral lines have a larger blueshift, while star B's spectral lines have a smaller redshift.
C) Star A's spectral lines have a smaller redshift, while star B's spectral lines have a larger blueshift.
D) Star A's spectral lines have a larger redshift, while star B's spectral lines have a smaller blueshift.

Question 30

Which of the following is necessary to construct a modern model of a star?

A) equations of hydrostatic equilibrium
B) computers
C) equations of energy transport
D) all of the above

Question 31

The figure below shows four stars on an HR diagram.Which star has the largest radius?

A) A
B) B
C) C
D) D

Question 32

A stellar model:

A) requires a model for the formation of the star.
B) requires detailed observations of a star's interior.
C) predicts the nature of energy transport within the star.
D) all of the above.

Question 33

Which of the following environments would allow astronomers to produce an HR diagram that includes all phases of stellar evolution for stars with a wide range of masses?

A) an open cluster of stars that formed less than 10⁶ years ago
B) a globular cluster of stars that formed 10¹⁰ years ago
C) an open cluster of stars that formed 10¹⁰ years ago
D) a galactic center field with a mixture of ages

Question 34

Star A is twice as luminous as star B but has half the temperature of star B.How large is the radius of star A compared to star B?

A) 23/2 as large
B) 22 as large
C) 25/2 as large
D) 23 as large

Question 35

Over the course of their hydrogen-fusing lives,stars:

A) move along the main sequence, from left to right.
B) remain in nearly the same location on the main sequence.
C) move along the main sequence, from right to left.
D) move up the red giant branch.

Question 36

Suppose that astronomers discover an error in our understanding of Cepheid variable stars,such that stars of a given oscillation period have a smaller luminosity than previously assumed.How would that change the estimated distances to other galaxies?

A) The distance estimates would not change.
B) The distance estimates would have greater variation.
C) The distance estimates would become larger.
D) The distance estimates would become smaller.

Question 37

Stellar evolution has been best understood by:

A) analyzing the properties of a large number of stars at a single instant.
B) observing the entire life cycles of individual high-mass stars.
C) measuring stars moving along the main sequence.
D) computer models without the input of observations.

Question 38

Massive stars:

A) burn their fuel rapidly, so they have shorter lifetimes than low-mass stars.
B) have large fuel supplies, so they have longer lifetimes than low-mass stars.
C) use the efficient CNO cycle, so they have longer lifetimes than low-mass stars.
D) burn more elements, so they have longer lifetimes than low-mass stars.

Question 39

Star A is four times as luminous as star B.Star B's spectrum peaks at 300 nm,while star A's spectrum peaks at 150 nm.How large is the radius of star A compared to star B?

A) 1/2 as large
B) 1/4 as large
C) twice as large
D) four times as large

Question 40

Which of the following stellar spectral types shows the most molecular absorption lines?

A) O
B) A
C) M
D) G

Question 41

A stellar evolutionary track is the sequence of:

A) spatial locations occupied by a star over its lifetime.
B) luminosities and surface temperatures of a star over its lifetime.
C) fuel supplies of a star over its lifetime.
D) star formation and supernovae in a galaxy.

Question 42

A star has a surface temperature of 15,000 K.At what wavelength does the star produce the most energy?

Question 43

An astronomer studies two globular clusters,A and B.Cluster A has a higher metallicity than cluster B,but their properties are otherwise identical.The astronomer should expect that:

A) cluster A's main sequence turnoff occurs at a higher mass than cluster B.
B) cluster A is more distant than cluster B.
C) cluster A is older than cluster B.
D) cluster A is more massive than cluster B.

Question 44

What is an astrometric binary?

Question 45

Why does the nature of a star's energy source require a star to change over time?

Question 46

Stars A and B are identical,except that star A has a parallax of 0.1 arcseconds while star B has a parallax of 0.4 arcseconds.How does the brightness of stars A and B compare?

Question 47

Why are globular clusters useful for studies of stellar evolution?

A) Their stars span a wide range of masses.
B) Their stars are the same age.
C) Their stars all have the same composition.
D) All of the above.

Question 48

Star A moves 1 arcsecond/year across the sky while star B moves 0.5 arcseconds/year.Star A has a parallax angle three times as large as star B.If neither star shows a Doppler effect,how do the space velocities of the two stars compare to each other?

Question 49

Which of the following quantities changes significantly during a star's main sequence lifetime?

A) luminosity
B) mass
C) core composition
D) color

Question 50

How do astronomers determine the composition of stars?

Question 51

An astronomer observes a cluster of stars and constructs an HR diagram like Figure 11.6.What can he or she learn from the region marked "X"?

A) the distance to the cluster
B) the radius of the cluster
C) the mass of the cluster
D) the age of the cluster

Question 52

Star A has an apparent magnitude of 5,while star B has an apparent magnitude of 10.If star A is twice as far from Earth as star B,how do the luminosities of the two stars compare?

Question 53

What information do you need to calculate the apparent magnitude of a star? What about the absolute magnitude?

Question 54

If a star is so large that it cannot be resolved by a telescope on (or near)Earth,what quantities must you measure to determine its radius?

Question 55

A star 10 times more massive than the Sun fuses hydrogen to helium 3,000 times faster than the Sun.If the Sun spends 10 billion years on the main sequence,how long will the more massive star remain there?

A) 10¹¹ years
B) 10⁹ years
C) 3 × 10⁷ years
D) 3 × 10⁶ years

Question 56

Which of the following quantities is NOT necessary to observe in order to construct an HR diagram of a system of stars?

A) distance to each star
B) mass of each star
C) color of each star
D) brightness of each star

Question 57

What property of Cepheid variable stars makes them useful for distance measures?

Question 58

What will happen when the Sun runs out of hydrogen fuel for fusion?

A) It will explode in a supernova.
B) Its internal structure will change.
C) It will begin fusing helium.
D) It will become a white dwarf.

Question 59

Which of the following inputs are necessary for astronomers to compute the stellar evolutionary track of a star?

A) mass and surface temperature
B) mass and luminosity
C) mass and composition
D) luminosity and surface temperature

Question 60

What causes a star to leave the main sequence?

A) the decreasing temperature of the star
B) the decreasing temperature of the star's core
C) the consumption of all the star's hydrogen
D) the consumption of the stellar core's hydrogen

Question 61

How does the inclination of a spectroscopic binary star system's orbit affect astronomers' mass estimates of the stars?

Question 62

Why does luminosity increase with stellar mass on the main sequence?

Question 63

The Sun is expected to spend about 5 billion more years on the main sequence.If its luminosity increased suddenly to four times its usual value,how much time would it remain on the main sequence?

Question 64

Draw an HR diagram and sketch the location of the main sequence,red giant branch,and white dwarfs.

Question 65

What is the name for the force balance illustrated in the figure below?

Question 66

In a typical observation of a globular cluster,90% of the observed stars will lie on the main sequence.What does this tell you about the life cycle of stars?

Question 67

How do astronomers construct stellar evolutionary tracks on the HR diagram?

Question 68

All observed stars have roughly the same amount of hydrogen in their atmospheres.Why then are hydrogen lines less prominent in O stars than they are in A stars?

Question 69

How are globular clusters used to test stellar models?

Question 70

What aspects of a star change significantly during its time on the main sequence?