Deck 13: Taking the Measure of Stars

Question 1

Spectra of the least massive main-sequence stars show the largest amount of absorption from molecules like TiO and CN.

Answer 1

True

Question 2

A star's mass is the only characteristic that determines its position in the H-R diagram.

Answer 2

False

Question 3

Parallax is used to measure a star's:

A) distance
B) velocity
C) luminosity
D) mass
E) radius

Answer 3

distance

Question 4

What advantage do you gain by having two eyes that are separated on your face, rather than being very close together?

A) better collecting area, which allows you to see dimmer objects
B) double vision, which allows you to see multiple objects at once
C) color vision, which allows you to determine temperatures
D) stereoscopic vision, which allows you to determine distances
E) better magnification, which allows you to see smaller objects

Question 5

The absolute magnitude of a star is a measure of its luminosity.

Question 6

How many arcseconds are there in 1 degree?

A) 60
B) 360
C) 3,600
D) 6,000
E) 36,000

Question 7

To measure the parallax of the most distant stars measurable, we would make two measurements of the star's position on the sky separated by:

A) 6 hours
B) 12 hours
C) 24 hours
D) 6 months
E) 12 months

Question 8

With today's advanced technology, we can measure the parallax for any star inside the Milky Way.

Question 9

If a star's distance is 10 pc, what is its parallax?

A) 0.01 arcsec
B) 0.05 arcsec
C) 0.1 arcsec
D) 0.5 arcsec
E) 1 arcsec

Question 10

Two main-sequence stars have the same temperature. If star A is four times brighter than star B, then:

A) star B is two times farther away than star A
B) star B is four times farther away than star A
C) star B is eight times farther away than star A
D) star B and star A lie at the same distance from us
E) it is impossible to determine their relative distances from the information given

Question 11

A parsec is a unit of time.

Question 12

If a star's measured parallax is 0.2 arcsec, what is its distance?

A) 2 pc
B) 5 pc
C) 20 pc
D) 40 pc
E) 50 pc

Question 13

Binary star systems are extremely useful in studying stars because they allow us to determine stars' masses.

Question 14

Stars that have spectral type B are lower in temperature than spectral type M.

Question 15

The stars that have the largest radii are classified as supergiants.

Question 16

Stars with a larger brightness must be closer to us than fainter stars.

Question 17

Stars A and B appear equally bright, but star A is twice as far away from us as star B. Which of the following is true?

A) Star A is twice as luminous as star B.
B) Star A is four times as luminous as star B.
C) Star B is twice as luminous as star A.
D) Star B is four times as luminous as star B.
E) Star A and star B have the same luminosity because they have the same brightness.

Question 18

A star's mass determines where it lies on the main sequence of an H-R diagram.

Question 19

Stars of spectral class O have the strongest hydrogen absorption lines, whereas stars of spectral class M have the weakest hydrogen absorption lines.

Question 20

How is the distance to a star related to its parallax?

A) Distance is directly proportional to parallax.
B) Distance is inversely proportional to parallax.
C) Distance is directly proportional to parallax squared.
D) Distance is inversely proportional to parallax squared.
E) Distance and parallax are not related to each other at all.

Question 21

Star A and star B both have the same temperature but different sizes and distances. As a result, star A is more luminous than star B, but star B is brighter than star A. Which of these statements about the absolute and apparent magnitudes of the two stars is correct?

A) Star A has a larger apparent magnitude and a larger absolute magnitude.
B) Star A has a larger apparent magnitude, while star B has a larger absolute magnitude.
C) Star B has a larger apparent magnitude and a larger absolute magnitude.
D) Star B has a larger apparent magnitude, while star A has a larger absolute magnitude.
E) Both stars have the same apparent and absolute magnitudes.

Question 22

Star E is the same temperature as star F, but star E is four times as luminous as star F. How do the radii of the stars compare?

A) Star E has twice the radius of star F.
B) Star E has four times the radius of star F.
C) Star F has twice the radius of star E.
D) Star F has four times the radius of star E.
E) They are the same size.

Question 23

Star A is a red star. Star B is a blue star. Which star is hotter?

A) Star A is hotter.
B) Star B is hotter.
C) They are the same temperature.
D) We also need to know the luminosities of the stars to determine their temperatures.
E) Color is not related to temperature at all.

Question 24

If we know the temperature and luminosity of a star, we can also calculate its:

A) radius
B) mass
C) chemical composition
D) brightness
E) all of the above

Question 25

Two stars with similar temperatures but different sizes will have:

A) similar spectral types but different luminosities
B) similar luminosities but different brightnesses
C) similar brightnesses but different distances
D) similar distances but different masses
E) similar masses but different spectral types

Question 26

Stars are made mostly of:

A) helium
B) oxygen
C) hydrogen
D) nitrogen
E) carbon

Question 27

What type of spectrum do most stars produce?

A) an absorption spectrum on top of a blackbody spectrum
B) an emission spectrum on top of a blackbody spectrum
C) an absorption spectrum on top of an emission spectrum
D) a pure emission spectrum
E) a pure blackbody spectrum

Question 28

A star classified as a K0III star is:

A) a giant that is cooler than the Sun
B) a supergiant that is hotter than the Sun
C) a main-sequence star that is hotter than the Sun
D) a subgiant that is cooler than the Sun
E) a dwarf that is hotter than the Sun

Question 29

You observe two stars in a visual binary system using a blue filter that is centered at a wavelength of 550 nm and a red filter that is centered at a wavelength of 650 nm. Star A has a temperature of 10,000 K, while star B has a temperature of 4000 K, and you know that both stars are the same size. Which star will be the brightest in each filter?

A) Star A is the brightest in the blue filter, and star B is the brightest in the red filter.
B) Star B is the brightest in the blue filter, and star A is the brightest in the red filter.
C) Star A is the brightest in both filters.
D) Star B is the brightest in both filters.
E) Both stars have the same brightness in each filter.

Question 30

The star named Capella has an apparent magnitude of 0, while the star named Polaris has an apparent magnitude of 2, which means that Capella is _________ than Polaris.

A) 18 times fainter
B) 6 times fainter
C) 2 times fainter
D) 2 times brighter
E) 6 times brighter

Question 31

The fraction of the Sun's mass that is made of heavy elements is:

A) 0.5 percent
B) 2 percent
C) 10 percent
D) 20 percent
E) 50 percent

Question 32

The spectral class of a star is related to its:

A) luminosity
B) brightness
C) radius
D) mass
E) temperature

Question 33

What spectral class is the Sun?

A) A0
B) B7
C) F5
D) M3
E) G2

Question 34

Star A is a red star. Star B is a blue star. You are able to determine that both stars are the same size. Which star is more luminous?

A) Star A is more luminous.
B) Star B is more luminous.
C) They have the same luminosities.
D) We also need to know the distance of the stars to determine their luminosity.
E) We cannot tell because color is not related to luminosity.

Question 35

Star C is a red star. Star D is a blue star. Which has a larger radius?

A) Star C has a larger radius.
B) Star D has a larger radius.
C) Stars C and D have the same radius.
D) We also need to know the luminosities of the stars to determine their radii.
E) We cannot determine the radii because color is not related to the radius.

Question 36

When astronomers refer to "heavy elements," which elements are they talking about?

A) all elements
B) all elements more massive than hydrogen
C) all elements more massive than helium
D) all elements more massive than carbon
E) all elements more massive than iron

Question 37

What is the difference between brightness and luminosity?

A) These are different names for the same property.
B) Luminosity is how much light we see from a star; brightness is how much light it emits.
C) Brightness is how much light we see from a star; luminosity is how much light it emits.
D) Luminosity measures size; brightness measures temperature.
E) Brightness measure size; luminosity measures temperature.

Question 38

Which sequence correctly lists the spectral classes of stars in order from hottest to coolest?

A) A B F G K M O
B) O A B G F M K
C) A F O B M G K
D) O B A F G K M
E) M K G F A B O

Question 39

Star A is a red star. Star B is a blue star. You are able to determine that both stars are the same size. Which star is brighter?

A) Star A is brighter.
B) Star B is brighter.
C) They have the same brightness.
D) We also need to know the distance of the stars to determine their brightness.
E) Color is not related to brightness at all.

Question 40

Why do O- and B-type stars have weaker hydrogen absorption lines than A-type stars?

A) O- and B-type stars are cooler than A-type stars.
B) O- and B-type stars are smaller than A-type stars.
C) A larger fraction of hydrogen atoms in O- and B-type stars is ionized.
D) O- and B-type stars have converted much more of their hydrogen into heavier elements.
E) A-type stars have a higher mass than O- and B-type stars, so they have more hydrogen.

Question 41

Stars X and Y are 5 AU apart from each other. Star X is four times as massive as star Y. The center of mass of this system is _________ AU away from star X and _________ AU away from star Y.

A) 3; 2
B) 2; 3
C) 2.5; 2.5
D) 1; 4
E) 4; 1

Question 42

You discover a binary star system in which star A has a velocity of 10 km/s and star B has a velocity of 30 km/s. If you study the system further and find out that the orbital period is 30 days and the orbital separation is a constant 0.3 AU, then what are the masses of stars A and B?

A) Star A is 3M _$\odot$ , and Star B is 1M _$\odot$ .
B) Star A is 1M _$\odot$ , and Star B is 0.3M _$\odot$ .
C) Star A is 6M _$\odot$ , and Star B is 2M _$\odot$ .
D) Star A is 2M _$\odot$ , and Star B is 0.5M _$\odot$ .
E) Star A is 0.3M _$\odot$ , and Star B is 1M _$\odot$

Question 43

Astronomers can measure the speed of the stars in a binary system by measuring the _________ of the stars.

A) temperatures
B) luminosities
C) distance
D) colors
E) spectra

Question 44

Figure 1
Figure 1 shows an H-R diagram, with five stars labeled A through E. Which star has the largest temperature?

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

Question 45

Which of the following properties are NOT useful in determining the masses of stars in a typical binary system?

A) The period of the orbits of the two stars is not useful.
B) The average separation between the two stars is not useful.
C) The radii of the two stars is not useful.
D) The velocities of the two stars is not useful.
E) All of the above are useful for determining the masses of stars in a binary.

Question 46

If star A has a temperature that is twice as hot as the Sun but has the same luminosity as the Sun, the diameter of star A must be _________ times the diameter of the Sun.

A) 16
B) 4
C) 2
D) 1/2
E) 1/4

Question 47

Roughly what percentage of stars in our galaxy are main-sequence stars?

A) 10 percent
B) 25 percent
C) 50 percent
D) 75 percent
E) 90 percent

Question 48

For which type of binary system are astronomers able to resolve each of the two stars individually?

A) eclipsing binary
B) spectroscopic binary
C) visual binary
D) binaries where the two stars have the same mass
E) binaries where the two stars have the same luminosity

Question 49

Main-sequence stars range in mass from approximately:

A) 0.5 to 10 M _$\odot$
B) 0.08 to 150 M _$\odot$
C) 1 to 100 M _$\odot$
D) 0.1 to 75 M _$\odot$
E) 5 to 50 M _$\odot$

Question 50

Which stars are the most common?

A) Stars with a larger mass and a larger radius than the Sun's are the most common.
B) Stars with a smaller mass and a smaller radius than the Sun's are the most common.
C) Stars with a larger mass and a smaller radius than the Sun's are the most common.
D) Stars with a smaller mass and a larger radius than the Sun's are the most common.
E) All of the above are equally common.

Question 51

The Hertzsprung-Russell diagram is a graph of _________ for stars.

A) mass versus brightness
B) size versus mass
C) luminosity versus temperature
D) mass versus spectral type
E) luminosity versus brightness

Question 52

Figure 1
Figure 1 shows an H-R diagram, with five stars labeled A through E. Which star has the smallest radius?

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

Question 53

On a typical H-R diagram, where are the stars with the largest radii located?

A) in the upper left corner
B) in the upper right corner
C) in the center
D) in the lower left corner
E) in the lower right corner

Question 54

In a binary star system that contains stars with 2M _$\odot$ and 1M _$\odot$ , the velocity of the 2M _$\odot$ star will be _________ times the velocity of the 1M _$\odot$ star.

A) 0.2
B) 0.5
C) 1
D) 2
E) 3

Question 55

Which of the following properties would not be plotted on the horizontal axis of an H-R diagram?

A) Color would not be plotted.
B) Luminosity would not be plotted.
C) Temperature would not be plotted.
D) Spectral class would not be plotted.
E) All of the above are plotted on the horizontal axis of an H-R diagram.

Question 56

Eclipsing binary systems:

A) orbit in the plane of the sky
B) exhibit large radial velocity shifts
C) contain equal mass stars
D) contain stars that pass in front of one another during their orbit
E) contain stars that can be resolved as two separate stars

Question 57

What type of star is most common in the solar neighborhood?

A) subgiants
B) supergiant
C) white dwarf
D) giant
E) main-sequence

Question 58

Figure 1
Figure 1 shows an H-R diagram, with five stars labeled A through E. Which star has the largest luminosity?

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

Question 59

The faster-moving star in a binary is:

A) the less massive star
B) the more massive star
C) the smaller radius star
D) the larger radius star
E) the lower temperature star

Question 60

The bright star named Rigel has a luminosity of 66,000 L _$\wedge$ and a temperature of 11,000 K. What is its radius? Note that the temperature of the Sun is 5,800 K.

A) 5 R _$\odot$
B) 30 R _$\odot$
C) 70 R _$\odot$
D) 135 R _$\odot$
E) 190 R _$\odot$

Question 61

The brightest stars in the sky also tend to be:

A) the highest mass stars
B) the hottest stars in the sky
C) very near to us
D) very luminous
E) all of the above

Question 62

What are the two main chemical elements that make up the Sun? How much of the mass of the Sun is composed of elements other than these two?

Question 63

Star A is exactly the same color as star B and appears equally bright. Through stellar parallax measurements, we find that star B is twice as far away from us as star A. Determine which star has the largest radius and how much larger it is.

Question 64

A star with a stellar parallax of 0.025 arcseconds has a distance of how many parsecs?

Question 65

What is the spectral type of stars that have the strongest hydrogen absorption lines? Why do stars that are hotter than these have weaker hydrogen lines?

Question 66

Explain how astronomers can use the blue and visual filters to determine the temperatures of stars.

Question 67

In which region of an H-R diagram would you find the main-sequence stars with the widest habitable zones?

A) upper left
B) upper right
C) center
D) lower left
E) lower right

Question 68

Rigel is a star with an apparent magnitude of +0.1, and Betelgeuse is a star with an apparent magnitude of +0.4. Which star appears brighter, and what is the ratio of their brightnesses?

Question 69

What is the approximate luminosity of a 5 M _$\odot$ main-sequence star?

A) 50 L _$\odot$
B) 80 L _$\odot$
C) 150 L _$\odot$
D) 280 L _$\odot$
E) 510 L _$\odot$

Question 70

The bright star Arcturus has a luminosity of 210 L _$\odot$ and a temperature of 4300 K. What is its radius? Note that the Sun has a temperature of 5800 K.

Question 71

The one property of a main-sequence star that determines all its other properties is its:

A) luminosity
B) mass
C) temperature
D) spectral type
E) brightness

Question 72

The picture below shows an H-R diagram, with five stars labeled A through E. Which of the main-sequence stars has the smallest mass?

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

Question 73

The habitable zone for the Sun covers the area that is between _________ from the Sun.

A) 0 to 0.8 AU
B) 0.5 to 10 AU
C) 1.2 to 4.2 AU
D) 0.9 to 1.4 AU
E) 0.2 to 10.2 AU

Question 74

How is the unit of length known as a parsec defined?

Question 75

If we measure a star's luminosity and temperature, what other property of the star can we calculate? Explain how.

Question 76

If the Hubble space telescope can see stars as faint as magnitude 27, how much fainter are these stars than the faintest ones you can see in a very dark night sky, which have magnitude 6?

Question 77

The blackbody spectra of a star with a temperature of 6000 K and a star with a temperature of 4000 K are shown below. An astronomer uses a telescope to observe each of these two stars in both the blue and red filters. The blue filter is centered at 450 nm, while the red filter is centered at 660 nm. For each of the two stars, state through which filter that star will be the brightest. Explain your answer.

Question 78

If a star's parallax is measured using identical telescopes, one on Earth and the other on Mars, which planet's telescope would measure the biggest parallax? Explain your answer.

Question 79

The stars that have the largest radii are classified as:

A) giants
B) ultragiants
C) supergiants
D) megagiants
E) supernovae

Question 80

What is the approximate luminosity of a 0.5 M _$\odot$ main-sequence star?

A) 0.09 L _$\odot$
B) 0.01 L _$\odot$
C) 0.2 L _$\odot$
D) 0.5 L _$\odot$
E) 0.7 L _$\odot$