Deck 10: Measuring the Stars

Question 1

Mass determines the position of a star on the main sequence.

Answer 1

True

Question 2

An emission line is produced when an atom absorbs a photon of a specific energy.

Answer 2

False

Question 3

A thin cloud of cool gas on top of a hotter blackbody will radiate an emission spectrum.

Answer 3

False

Question 4

Among main-sequence stars,the most massive stars are more luminous,redder,cooler,and have larger radii than less massive stars.

Question 5

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

Question 6

Stars of spectral class A have the most hydrogen whereas stars of spectral class O have the least hydrogen.

Question 7

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

Question 8

Excluding the Sun,not a single star has an observed parallax greater than 1 arcsecond.

Question 9

When looking at a standard H-R diagram,the hottest stars are on the left-hand side of the diagram.

Question 10

Spectra of the coolest stars show the largest amount of absorption from molecules like TiO and CN.

Question 11

A parsec is a unit of time.

Question 12

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

Question 13

A star with the same luminosity as the Sun,but which is twice as hot,must be four times as big.

Question 14

It is not possible to detect a measurable parallax for even the closest stars without the use of a telescope.

Question 15

Heisenberg's uncertainty principle tells us that an electron in an atom behaves more like a cloud than a pointlike particle.

Question 16

Mass solely determines the position of a star on the H-R diagram.

Question 17

The emission and absorption lines of a given atom occur at the exact same energies.

Question 18

The emission spectrum of a helium atom is identical to that of a carbon atom.

Question 19

Stars with a higher apparent brightness are necessarily closer to us than fainter stars.

Question 20

B stars are cooler than M stars.

Question 21

The spectrum in the figure below is:

A) an absorption spectrum
B) an emission spectrum
C) a thermal spectrum
D) not any of these types

Question 22

Stars are made mostly of:

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

Question 23

Which star in the figure below is closest to Earth?

A) Star A
B) Star B
C) The two stars are the same distance
D) Not enough information

Question 24

Stars of similar temperatures but different sizes:

A) will have similar luminosities but different masses
B) will have similar masses but different distances
C) will have different spectral types but similar luminosities
D) will have similar spectral types but different luminosities

Question 25

What spectral class is the Sun?

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

Question 26

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

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

Question 27

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

Question 28

A star emits:

A) an absorption spectrum
B) a continuous spectrum
C) an emission spectrum
D) no radiation

Question 29

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.

Question 30

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

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

Question 31

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 appears __________ Polaris in the night sky.

A) brighter than
B) as bright as
C) dimmer than

Question 32

What is the difference between brightness and luminosity?

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

Question 33

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.

Question 34

Which sequence correctly lists the spectral classes of stars in order of decreasing temperature (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

Question 35

The spectral class of a star is related to its:

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

Question 36

When an electron moves from a higher energy level in an atom to a lower energy level:

A) the atom is ionized
B) a continuous spectrum is emitted
C) a photon is emitted
D) a photon is absorbed

Question 37

Two similar 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 and Star A lie at the same distance from us
D) it is impossible to determine their relative distances from the information given

Question 38

Parallax is used to measure:

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

Question 39

How many arcseconds are there in a degree?

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

Question 40

In the quantum mechanical view of the atom,an electron is best thought of as:

A) a cloud that is centered on the nucleus
B) a pointlike particle orbiting the nucleus
C) free to orbit at any distance from the nucleus
D) all of the above are true

Question 41

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 0.3 AU then what are the masses of stars A and B?

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

Question 42

All of the following are useful in determining the masses of stars in a binary system EXCEPT:

A) the period of the orbits of the two stars
B) the average separation between the two stars
C) the luminosities of the two stars
D) the velocities of the two stars

Question 43

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

Question 44

Roughly what percentage of stars are main-sequence stars?

A) 10 percent
B) 40 percent
C) 60 percent
D) 90 percent

Question 45

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

Question 46

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

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

Question 47

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

Question 48

Stars X and Y are 5 AU apart from each other.Star X is 4 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) 1; 4
B) 2; 3
C) 3; 2
D) 4; 1

Question 49

The Hertzsprung-Russell diagram (figure below)is:

A) a graph of mass versus brightness for stars
B) a graph of size versus mass for stars
C) a graph of surface temperature versus luminosity for stars
D) a graph of mass versus spectral type for stars

Question 50

Main-sequence stars range in mass from approximately:

A) 0.5 to 10 M _$\bigodot$
B) 0.08 to 140 M _$\bigodot$
C) 1 to 100 M _$\bigodot$
D) 0.1 to 75 M _$\bigodot$

Question 51

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

Question 52

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

A) In the upper left corner
B) In the upper right corner
C) In the lower left corner
D) In the lower right corner

Question 53

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

A) Color
B) Luminosity
C) Temperature
D) Spectral class

Question 54

The stars that have the largest radii are classified as:

A) giants
B) ultragiants
C) supergiants
D) dwarfs

Question 55

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

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

Question 56

Examine the figure below.On a typical H-R diagram,where are main-sequence stars that have the coolest surface temperatures located?

A) In the upper left corner
B) In the upper right corner
C) In the lower left corner
D) In the lower right corner

Question 57

Examine the figure below.On a typical H-R diagram,where are main-sequence stars that have the hottest surface temperatures located?

A) In the upper left corner
B) In the upper right corner
C) In the lower left corner
D) In the lower right corner

Question 58

The faster-moving star in a binary is:

A) the less massive star
B) the more massive star
C) the hotter star
D) the more distant of the two stars

Question 59

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

Question 60

Describe how brightness,luminosity,and distance are related?

Question 61

In what ways are energy states of an atom like books occupying shelves in a bookcase?

Question 62

What is the main property of a main-sequence star that determines nearly all its other properties?

Question 63

Explain how we can use spectroscopic parallax to determine the distance to a star farther away than a few hundred light-years.

Question 64

You observe a binary star system and find that star 1 has a velocity of 10 m/s while star 2 has a velocity of 35 m/s.What is the ratio of masses of the two stars (M₁/M₂)?

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

Describe the luminosity classes found on the H-R diagram below.

Question 67

You observe a binary star system and find that star 1 has a velocity of 20 m/s while star 2 has a velocity of 40 m/s.What is the ratio of masses of the two stars (M₁/M₂)? If you find that the separation of the two stars is 0.5 AU and the orbital period is 70 days,then what are the individual masses of the two stars?

Question 68

Using information from the figure below,explain why star 2 is the more massive star of the eclipsing binary pair?

Question 69

How do astronomers use spectra to determine the composition of a star?

Question 70

If given the image in the figure below alone,what further information might be required to determine that the stars are a visual binary system?

Question 71

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

Question 72

How are atoms excited and why do they decay?

Question 73

Examine the figure below.Along the main sequence,how do the luminosity,temperature,radius,and mass of stars change as you go from the upper-left to the lower-right corners of the H-R diagram?

Question 74

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 75

Why do we see black lines in an absorption spectrum if the absorbed photons are (almost)instantaneously reemitted by the atoms in the cloud?