Deck 13: Taking the Measure of Stars

Question 1

We can measure the luminosity of a star just from its color.

Answer 1

False

Question 2

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

Answer 2

True

Question 3

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.

Answer 3

6 months.

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

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 6

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

Question 7

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

Question 8

B stars are cooler than M stars.

Question 9

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

Question 10

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

Question 11

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

Question 12

A parsec is a unit of time.

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

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

Question 18

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 19

Parallax is used to measure

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

Question 20

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

Question 21

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 22

Star E is the same temperature as star F but is four times as luminous.Which star is bigger?

A) Star E is twice as big as star F.
B) Star E is four times as big as star F.
C) Star F is twice as big as star E.
D) Star F is four times as big as star E.

Question 23

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 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

Stars are made mostly of

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

Question 26

How many arcseconds are there in a degree?

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

Question 27

The fraction of mass in the Sun that is made of heavy elements is

A) 0.5 percent.
B) 2 percent.
C) 10 percent.
D) 20 percent.

Question 28

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 29

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) 6 times fainter
B) 2 times fainter
C) 6 times brighter
D) 2 times brighter

Question 30

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

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

Question 31

The spectral class of a star is related to its

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

Question 32

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 33

What spectral class is the Sun?

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

Question 34

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

A) radius.
B) mass.
C) chemical composition.
D) All of the above

Question 35

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

A) 5
B) 30
C) 70
D) 190

Question 36

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 37

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 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

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 39

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 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) 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 41

Main-sequence stars range in mass from approximately

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

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

A) Star A is and Star B is .
B) Star A is and Star B is .
C) Star A is and Star B is .
D) Star A is and Star B is .

Question 43

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 44

Roughly what percentage of stars are main-sequence stars?

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

Question 45

The Hertzsprung-Russell Diagram is

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

Question 46

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

Question 47

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

A) Main sequence
B) Supergiant
C) White Dwarf
D) Giant

Question 48

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 49

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 50

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 51

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 52

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

Question 53

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 54

The stars that have the largest radii are classified as

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

Question 55

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 56

In a binary star system that contains stars with and ,the velocity of the star will be __________ times the velocity of the star.

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

Question 57

The brightest stars in the sky also tend to be

A) very luminous.
B) the hottest stars in the sky.
C) very near to us.
D) All of the above

Question 58

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 59

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

Question 60

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 61

Star A emits its peak energy at a wavelength of 500 nm;star B emits its peak energy at a wavelength of 750 nm.If both stars have the same radii,which star is hotter and by how much?

Question 62

The bright star Arcturus has a luminosity of and a temperature of 4,300 K.What is its radius? Note that the Sun has a temperature of 5,800 K.

Question 63

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

Question 64

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 65

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

Question 66

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 ? 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 67

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

Question 68

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

Question 69

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 ?

Question 70

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?