Download Labeling the HR Diagram - Mastering Physics Answers

Mandatory Assignment 3­ testing material from Chaper 15
Labeling the H­R Diagram
Learning Goal:
To identify key features of the H­R diagram.
Part A
The figure shows a standard Hertzsprung­Russell (H­R) diagram. Label the horizontal and vertical axes using the two blanks nearest the center of each
axis, and label the extremes on the two axes using the blanks on the ends of the axes.
Drag the labels to the blanks on the diagram.
Hint 1. Where do spectral types appear on the H­R diagram?
The spectral types in the order OBAFGKM can be labeled from __________.
ANSWER:
bottom to top on the vertical axis
left to right on the horizontal axis
top to bottom on the vertical axis
right to left on the horizontal axis
ANSWER:
Correct
Note that any star can be plotted on the H­R diagram if you know its surface temperature and luminosity. Also recall that the horizontal axis can
be equivalently labeled with spectral type in the order OBAFGKM, because O stars are the hottest and M stars are the coolest.
Part B
Use the labels to identify what kinds of stars inhabit each region of the the H­R diagram.
Drag the labels to the blanks on the diagram. You may use labels more than once.
Hint 1. What is a supergiant?
A supergiant is a star that is extremely __________.
ANSWER:
1/29
Mandatory Assignment 3­ testing material from Chaper 15
hot
large and luminous
large but dim
Hint 2. How are spectral type, surface temperature, and luminosity related for main­sequence stars?
If you know the spectral type of a main­sequence star, then you also know __________.
ANSWER:
only its luminosity
only its surface temperature
both its surface temperature and luminosity
Hint 3. What is a white dwarf?
White dwarfs are __________.
ANSWER:
cool and dim
hot and luminous
hot and dim
ANSWER:
Correct
Stars are not uniformly spread out over the entire H­R diagram. Rather, they fall into several clear groups, each located in a different part of the
diagram.
Part C
The diagonal lines on the H­R diagram represent lines along which all stars would have the same radius. Label the three white lines with the correct
values for the radii of stars that fall on them.
Drag the labels to the blanks on the diagram.
Hint 1. Where is the Sun located on the H­R diagram?
On the H­R diagram, the Sun is located __________.
2/29
Mandatory Assignment 3­ testing material from Chaper 15
ANSWER:
at surface temperature of about 6000 K and luminosity of 1 (in solar units)
at surface temperature of about 20,000 K and luminosity of 10 −2 (in solar units)
at surface temperature of about 6000 K and luminosity of 10 5 (in solar units)
ANSWER:
Correct
Stellar radii increase diagonally on the H­R diagram from the lower left to the upper right.
Part D
The position of a star along the main sequence tells you both its mass and its hydrogen­burning lifetime. Label the indicated blanks on the main
sequence with the approximate lifetimes of stars at those positions.
Drag the labels to the blanks on the diagram.
Hint 1. How is a star's luminosity related to its fusion rate?
A high luminosity star has a very _____ rate of fusion.
ANSWER:
low
high
ANSWER:
3/29
2/20/2016
Mandatory Assignment 3­ testing material from Chaper 15
Correct
Stars spend most of their lives on the main sequence, where they generate energy by fusing hydrogen into helium in their cores. High­luminosity
stars have much shorter main­sequence lifetimes than lower luminosity stars, because they burn through their supply of hydrogen at a much
faster rate (which is also why they are so luminous).
Process of Science: Direct versus Indirect Measurements of Stellar Properties
Learning Goal:
To understand how we learn about stars through a combination of direct observations and quantities that we infer from data and calculations.
Part A
Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a
few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and
instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are
correct).
Hint 1. What is the difference between luminosity and apparent brightness?
Consider three stars that are all identical to the Sun, each one located at a different distance from Earth. Which of the following must be true?
ANSWER:
The stars all have the same luminosity but different apparent brightness.
The stars all have the same apparent brightness but different luminosity.
The stars all have the same luminosity and the same apparent brightness.
Hint 2. Is the inverse square law for the apparent brightness of light always valid?
Consider two stars that are identical to the Sun, but one is 10 times as far away as the other. According to the inverse square law for light, the
more distant star should appear dimmer by a factor of 10 2 = 100. But is this necessarily true in all cases?
ANSWER:
No. It is true only if no light from either star is absorbed or scattered away as the light travels from the star to Earth.
Yes. The inverse square law for light is an absolute law that is always valid.
No. The inverse square law for light is valid only for stars that are relatively nearby, not for stars at great distances from Earth.
Hint 3. What is a parallax angle used for?
If you know a star’s parallax angle, then you can calculate its _____.
4/29
2/20/2016
Mandatory Assignment 3­ testing material from Chaper 15
ANSWER:
mass
radius
distance
Hint 4. How do we know the temperature of the Sun’s photosphere?
We learn the temperature of the Sun’s photosphere by __________.
ANSWER:
sending space probes that carry thermometers into the photosphere
studying the Sun’s color and spectrum
applying the inverse square law for light
Hint 5. How do we find the masses of distant objects?
We can calculate the mass of a distant star by __________.
ANSWER:
applying the inverse square law for light
applying Newton’s version of Kepler’s third law
measuring its parallax angle
Hint 6. How do we determine the radius of a distant star?
The most common way of determining a star’s radius is to ___________.
ANSWER:
determine it from the star’s parallax angle
calculate it from the star’s luminosity and surface temperature
measure the star’s angular diameter in the sky
ANSWER:
5/29
Mandatory Assignment 3­ testing material from Chaper 15
All attempts used; correct answer displayed
Now continue to the follow­up questions to be sure you understand how we infer some of the properties of stars.
Part B
From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a
star’s surface temperature?
Hint 1. Which gas is hotter?
Consider three gas clouds consisting mostly of hydrogen. One cloud has most of its hydrogen in molecular form (H2), one has mostly neutral
hydrogen atoms, and one has mostly hydrogen ions (and free electrons). Which cloud is the hottest?
ANSWER:
the ionized cloud
the molecular cloud
the neutral cloud
ANSWER:
spectral type
apparent brightness
parallax angle
mass
Correct
A star’s spectral type (OBAFGKM) tells us its surface temperature, because different sets of lines form more easily at different temperatures.
Color can also be used as a rough measure of surface temperature; for example, a blue star is hotter than a red star.
Part C
Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?
Check all that apply.
Hint 1. What is the inverse square law for light?
Consider two stars that are all identical to the Sun, but one is 10 times as far away as the other. According to the inverse square law for light,
the more distant star should appear __________.
ANSWER:
dimmer by a factor of 10
dimmer by a factor of 10 2
= 100
brighter by a factor of 10
Hint 2. Can you determine the luminosity of a street light on a foggy night?
Suppose you measure the apparent brightness of a street light that is located 100 meters away from you. If it is a foggy night and you apply the
inverse square law for light, then the luminosity you calculate for the street light will be __________.
ANSWER:
accurate, because the inverse square law for light is always valid
too high, because the fog makes the light appear brighter than it really is
too low, because the fog absorbs some of the light, making the light appear dimmer than it really is
ANSWER:
6/29
Mandatory Assignment 3­ testing material from Chaper 15
We have measured the star’s distance.
We have measured the star’s spectral type.
No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star’s apparent brightness.
The star must be a member of a binary system.
Correct
We can use the inverse square law for light to calculate the star’s luminosity from its apparent brightness and distance. However, this calculated
value will be accurate only if there is no absorption or scattering of the light on its way from the star to us. (If there is interstellar dust between us
and the star, we can sometimes measure the amount and therefore determine the star's luminosity by accounting for the light this dust absorbs or
scatters.)
Part D
We found that mass must be inferred for the star described in Part A. However, we can measure a star’s mass directly if __________.
Hint 1. How do we know Earth’s mass?
Which two measured quantities can enable us to calculate Earth’s mass?
ANSWER:
Earth’s radius and Earth’s distance from the Sun
the Moon’s average distance from Earth and the Moon’s orbital period around Earth
Earth’s radius and Earth’s surface atmospheric pressure
ANSWER:
it is a member of an eclipsing binary system
we know its spectral type
it is near enough for us to measure its distance with parallax
it is unusually high in mass
Correct
We can use Newton’s version of Kepler’s third law to calculate the masses of distant objects, but only if we know the period and distance of an
orbiting object. This is possible for an eclipsing binary system, because the two stars orbit each other (and the eclipses tell us that we are viewing
the orbit edge­on).
Part E
You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we
cannot apply Newton’s version of Kepler’s third law. Which of the following must be true if the star’s inferred mass is to be accurate?
Check all that apply.
Hint 1. Do all G2 stars have the same mass as the Sun?
The Sun has spectral type G2, so we might expect another star of the same spectral type to be similar to the Sun in mass, luminosity, and
radius. However, this will be true only if the star is also __________.
ANSWER:
located within the Milky Way Galaxy
a main­sequence star
the same age as the Sun
ANSWER:
7/29
Mandatory Assignment 3­ testing material from Chaper 15
We have measured the star’s velocity.
The star must be located within the Milky Way Galaxy and not in another galaxy.
We have determined that the star is a main­sequence star.
We have measured the star’s spectral type.
Correct
All main­sequence stars of a particular spectral type have approximately the same mass. Therefore, if we know the star’s spectral type and know
that it is a main­sequence star, then we can infer its mass.
Ranking Task: H­R Diagram, Luminosity, and Temperature
Part A
Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.
Hint 1. How is the color of light related to its wavelength?
Which of the following lists the visible colors in correct order from shortest wavelength to longest wavelength?
ANSWER:
red, orange, green, blue
blue, green, orange, red
blue, orange, green, red
Hint 2. How does the wavelength of light depend on an object’s temperature?
According to the laws of thermal radiation, hotter objects have spectra that peak at __________.
ANSWER:
shorter wavelength
longer wavelength
Hint 3. The Color of the Sun
The Sun appears yellow or white to the eye, but its spectrum actually peaks in the middle of the visible region, which corresponds to yellow or
green in color. Note that this means the Sun's spectrum peaks at a wavelength longer than that of a blue star, but shorter than that of an orange
or red star.
ANSWER:
8/29
2/20/2016
Mandatory Assignment 3­ testing material from Chaper 15
Correct
Notice that temperature is related to color, and follows the order of the colors in the rainbow: Blue (or violet) stars are the hottest, while red stars
are the coolest. In the parts that follow, the H­R diagrams show the correlation between color and temperature on the horizontal axis.
Part B
Five stars are shown on the following H­R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars
have the same surface temperature, drag one star on top of the other(s).
Hint 1. How does the H­R diagram show surface temperature?
On the H­R diagram, surface temperature increases __________.
ANSWER:
upward, so stars low on the luminosity axis have lower surface temperature than stars higher up
right to left, so stars farther to the left along the spectral type axis have higher surface temperature than stars to the right
diagonally from the lower left to the upper right
ANSWER:
9/29
2/20/2016
Mandatory Assignment 3­ testing material from Chaper 15
Correct
All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature,
all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity.
Part C
Five stars are shown on the following H­R diagrams; notice that these are the same five stars shown in Part B. Rank the stars based on their
luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).
ANSWER:
Correct
Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the
luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and
E to investigate surface temperature and luminosity for a different set of five stars.
Part D
Five stars are shown on the following H­R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars
10/29
Mandatory Assignment 3­ testing material from Chaper 15
have the same surface temperature, drag one star on top of the other(s).
Hint 1. How does the H­R diagram show surface temperature?
On the HR diagram, surface temperature increases __________.
ANSWER:
upward, so stars low on the luminosity axis have lower surface temperature than stars higher up
right to left, so stars farther to the left along the spectral type axis have higher surface temperature than stars to the right
diagonally from the lower left to the upper right
ANSWER:
Correct
Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M
having the lowest surface temperature. In other words, spectral type increases to the left on the H­R diagram. Now proceed to Part E to determine
how these stars compare in luminosity.
Part E
Five stars are shown on the following H­R diagrams. Rank the stars based on their luminosity from highest to lowest; notice that these are the same
five stars shown in Part D. If two (or more) stars have the same luminosity, drag one star on top of the other(s).
ANSWER:
11/29
Mandatory Assignment 3­ testing material from Chaper 15
Correct
All five stars have the same luminosity because they are all at the same height along the vertical (luminosity) axis. Continue to Parts F and G for
more practice in reading surface temperature and luminosity on the HR diagram.
Part F
Five stars are shown on the following H­R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars
have the same surface temperature, drag one star on top of the other(s).
Hint 1. How does the H­R diagram show surface temperature?
On the H­R diagram, surface temperature increases __________.
ANSWER:
upward, so stars low on the luminosity axis have lower surface temperature than stars higher up
right to left, so stars farther to the left along the spectral type axis have higher surface temperature than stars to the right
diagonally from the lower left to the upper right
ANSWER:
12/29
2/20/2016
Mandatory Assignment 3­ testing material from Chaper 15
Correct
Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M
having the lowest surface temperature. In other words, spectral type increases to the left on the H­R diagram.
Part G
Five stars are shown on the following H­R diagrams; notice that these are the same five stars shown in Part F. Rank the stars based on their
luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).
ANSWER:
Correct
As always, the H­R diagram shows surface temperature along the horizontal axis and luminosity along the vertical axis.
Sorting Task: Patterns among Stars
13/29
Mandatory Assignment 3­ testing material from Chaper 15
Part A
Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.
Hint 1. What are giant and supergiant stars?
Giants and supergiants exceed most other stars in __________.
ANSWER:
surface temperature only
luminosity only
radius only
both radius and luminosity
both surface temperature and luminosity
Hint 2. What are main­sequence stars?
ANSWER:
Main­sequence stars are __________. a rare type of extremely massive star
stars that are in the longest­lasting phase of their lives, in which they fuse hydrogen into helium in their cores
stars that have exhausted their supplies of energy for fusion
Hint 3. What are white dwarfs?
ANSWER:
dim
White dwarfs are small and _____. very luminous
short lived
cool
ANSWER:
Correct
Be sure that you understand why each of these characteristics goes with either giants/supergiants, main­sequence stars, or white dwarfs. If you
are unsure, review the H­R diagram in your textbook.
Problem 15.51: Parallax and Distance
14/29
Mandatory Assignment 3­ testing material from Chaper 15
Use the parallax formula to calculate the distance to each of the following stars. Give your answers in both parsecs and light­years.
Part A
Alpha Centauri: parallax angle 0.7420''.
Express your answer using four significant figures.
ANSWER:
d
= 1.348 pc Correct
Part B
Express your answer using four significant figures.
ANSWER:
d
= 4.396 light − years Correct
Part C
Procyon: parallax angle of 0.2860''.
Express your answer using four significant figures.
ANSWER:
d
= 3.497 pc Correct
Part D
Express your answer using four significant figures.
ANSWER:
d
= 11.40 light − years Correct
Problem 15.54: Calculating Stellar Radii
Sirius A has a luminosity of 26L Sun and a surface temperature of about 9400 K .
Part A
What is its radius? (Hint: See Mathematical Insight Calculating Stellar Radii.)
Express your answer using two significant figures.
ANSWER:
R
= 1.3×109 m Correct
Problem 15.55: Lifetime as a Red Giant
The H­R diagram in the figure shows a star cluster with a large number of red giants in it.
15/29
Mandatory Assignment 3­ testing material from Chaper 15
Part A
What is the approximate mass of the most massive stars left on the main sequence of this star cluster?
ANSWER:
M ≈ 0.1M Sun
M ≈ 1M Sun
M ≈ 10M Sun
M ≈ 100M Sun
Correct
Part B
What is the luminosity of the most luminous stars in the cluster?
ANSWER:
L ≈ 1L Sun
L ≈ 10L Sun
L ≈ 100L Sun
L ≈ 1000L Sun
Correct
Part C
Compute the ratio between the luminosity from part B to the mass from part A. How does that ratio compare with the Sun's ratio of luminosity to
mass?
ANSWER:
L
M
= 1000
L Sun
MSun
Correct
Part D
Estimate the maximum amount of time these very luminous stars can last as red giants from your answer to part C.
ANSWER:
t ≈ 10
t ≈ 10
t ≈ 10
t ≈ 10
5
7
9
11
years
years
years
years
16/29
Mandatory Assignment 3­ testing material from Chaper 15
Correct
Problem 15.6
Part A
What do we mean by a star's spectral type? How is a star's spectral type related to its surface temperature and color? Which stars are hottest and
coolest in the spectral sequence OBAFGKM?
ANSWER:
3384 Character(s) remaining
Spectral characteristics offer a way to classify stars which gives information about temperature in a different ways.
Spectral lines can show if there are a lot of ionized elements in a star, which would indicate great heat. Stars with lots of molecules are relatively cool, otherwise the Submitted, grade pending
Visual Quiz
Part A
This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars,
and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius?
ANSWER:
It is actually a binary star system in which the second star is a white dwarf.
It is the most luminous star in this region of the sky.
It has the greatest apparent brightness of any star in this region of the sky.
It is the nearest star in this region of the sky.
All of the above are true.
Correct
It is the largest dot, and larger means brighter in this diagram.
Part B
17/29
Mandatory Assignment 3­ testing material from Chaper 15
Why do some of the bright stars (such as the one indicated by the arrow) in this photo have cross­shaped spikes over them?
ANSWER:
The spikes are an artifact of photography through a telescope.
Very bright stars tend to be slightly non­spherical in shape and therefore look like they have spikes in photos.
The stars with spikes are actually binary star systems.
The spikes are flares ejected from the surfaces of bright stars.
Correct
That's right: the spikes are not real, just artifacts of the observing process.
Part C
All the stars in this photo are at about the same distance from Earth (some 26,000 light­years away). Which stars in this picture are the largest in size
(radius)?
ANSWER:
The stars that have the spikes.
The bright red stars.
The blue/white stars that look largest on the photo.
The dim red stars.
Correct
These are red supergiants, and red giants are large in size.
Part D
18/29
Mandatory Assignment 3­ testing material from Chaper 15
This graph shows how the apparent brightness of an eclipsing binary system changes with time. Which of the four labeled regions represents the
system at a time when one star is eclipsing the other?
ANSWER:
I.
II.
Both II and IV.
IV.
Both I and III.
III.
Correct
The dips occur when one star eclipses the other.
Part E
Study this H­R diagram. What is the spectral type of the star Sirius?
ANSWER:
A.
Blue.
102.
Main sequence.
19/29
Mandatory Assignment 3­ testing material from Chaper 15
Correct
Spectral type is shown along the horizontal axis of the H­R diagram, and you can see that Sirius has spectral type A.
Part F
Study this H­R diagram. Which of the following stars is the most massive?
ANSWER:
Vega.
Bellatrix.
β
Centauri.
DX Cancri.
Correct
β
Centauri is highest up along the main sequence, which means it is the most massive.
Part G
20/29
Mandatory Assignment 3­ testing material from Chaper 15
Study this H­R diagram. Which of the following stars is the largest in size (radius)?
ANSWER:
Antares.
α
Centauri B.
Aldebaran.
Canopus.
Correct
Radius increases diagonally from lower left to upper right, and Antares is the farthest toward the upper right.
Part H
Study this H­R diagram. Which of the following stars has (or had) the longest hydrogen burning lifetime?
ANSWER:
21/29
Mandatory Assignment 3­ testing material from Chaper 15
Betelgeuse.
α
Centauri B.
Barnard's star.
The Sun.
Correct
It is the lowest mass star and hence has the longest lifetime.
Part I
This photo shows an object located in the halo of our Milky Way galaxy. What kind of object is it?
ANSWER:
A supergiant star.
An open cluster of stars.
A spiral galaxy.
A "beehive" cluster.
A globular cluster of stars.
Correct
Notice the "globule"­like shape.
Part J
22/29
Mandatory Assignment 3­ testing material from Chaper 15
This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they?
ANSWER:
Cool, red main­sequence stars of spectral type M.
Starspots.
Massive supergiant stars.
Old white dwarf stars that have turned red in color.
Red giant stars.
Correct
All the stars in a globular cluster are old and therefore low in mass, so the brightest ones must be red giants.
Problem 15.49: The Luminosity of Alpha Centauri A
Alpha Centauri A lies at a distance of 4.4 light­years and has an apparent brightness in our night sky of 2.7 × 10 −8 watt/m2 . Recall that 12
15
1 light − year = 9.5 × 10
km = 9.5 × 10
m.
Part A
Use the inverse square law for light to calculate the luminosity of Alpha Centauri A.
Express your answer using two significant figures.
ANSWER:
L
= 5.9×1026 watts Correct
Part B
Suppose you have a light bulb that emits 200 watts of visible light. (Note: This is not the case for a standard 200­watt light bulb, in which most of the
200 watts goes to heat and only about 20­30 watts is emitted as visible light.) How far away would you have to put the light bulb for it to have the
same apparent brightness as Alpha Centauri A in our sky? (Hint: Use 200 watts as L in the inverse square law for light, and use the apparent
brightness given above for Alpha Centauri A. Then solve for the distance.)
Express your answer using two significant figures.
ANSWER:
d
= 24 km Correct
23/29
Mandatory Assignment 3­ testing material from Chaper 15
Problem 15.52: The Magnitude System
Use the definitions of the magnitude system to answer each of the following questions.
Part A
Which is brighter in our sky, a star with apparent magnitude 2 or a star with apparent magnitude 12 ?
ANSWER:
A star with apparent magnitude 12.
A star with apparent magnitude 2.
Correct
Part B
By how much?
ANSWER:
F m=2
F m=12
= = 10000
Correct
Part C
Which has a greater luminosity, a star with absolute magnitude ­1 or a star with absolute magnitude 9 ?
ANSWER:
A star with absolute magnitude 9.
A star with absolute magnitude ­1.
Correct
Part D
By how much?
ANSWER:
L M=−1
L M=9
= = 10000
Correct
Problem 15.40: Stellar Data
Part A
The table below gives basic data for several bright stars; M v is absolute magnitude and mv is apparent magnitude. (Hint: Remember that the
magnitude scale runs backward, so that brighter stars have smaller (or more negative) magnitudes.)
Star
Aldebaran
Mv
mv
Spectral Type Luminosity Class
­0.2
+0.9
K5
III
+4.4
0.0
G2
V
Antares
­4.5
+0.9
M1
I
Canopus
­3.1
­0.7
F0
II
Fomalhaut
+2.0
+1.2
A3
V
Alpha Centauri A
24/29
Mandatory Assignment 3­ testing material from Chaper 15
Regulus
­0.6
+1.4
B7
V
Sirius
+1.4
­1.4
A1
V
Spica
­3.6
+0.9
B1
V
Use these data to answer the following questions. Include a brief explanation with each answer. Which star appears brightest in our sky?
ANSWER:
3794 Character(s) remaining
Sirius
Submitted, grade pending
Part B
Which star appears faintest in our sky?
ANSWER:
3793 Character(s) remaining
Regulus
Submitted, grade pending
Part C
Which star has the greatest luminosity?
ANSWER:
3793 Character(s) remaining
Antares
Submitted, grade pending
Part D
Which star has the least luminosity?
ANSWER:
3786 Character(s) remaining
Alpha Centauri
Submitted, grade pending
Part E
Which star has the highest surface temperature?
ANSWER:
25/29
Mandatory Assignment 3­ testing material from Chaper 15
3795 Character(s) remaining
Spica
Submitted, grade pending
Part F
Which star has the lowest surface temperature?
ANSWER:
3793 Character(s) remaining
Antares
Submitted, grade pending
Part G
Which star is most similar to the Sun?
ANSWER:
3786 Character(s) remaining
Alpha Centauri
Submitted, grade pending
Part H
Which star is a red supergiant?
ANSWER:
3789 Character(s) remaining
Antares..?a
Submitted, grade pending
Part I
Which star has the largest radius?
ANSWER:
3791 Character(s) remaining
Antares..
Submitted, grade pending
26/29
Mandatory Assignment 3­ testing material from Chaper 15
Part J
Which stars have finished burning hydrogen in their cores?
ANSWER:
3773 Character(s) remaining
Aldebaran, Antares, Conopus
Submitted, grade pending
Part K
Among the main­sequence stars listed, which one is the most massive?
ANSWER:
3795 Character(s) remaining
Spica
Submitted, grade pending
Part L
Among the main­sequence stars listed, which one has the longest lifetime?
ANSWER:
3785 Character(s) remaining
Alpha Centauri Submitted, grade pending
Visual Activity: Using an H­R Diagram to Explore the Properties of Main­Sequence Stars
First, launch the animation below. Explore the interactive figure before beginning to answer the questions. Click the “show stars” button to see the main
sequence and then move the “radius” slider (at bottom) to see the location along the main sequence of a main­sequence star with that particular radius.
You can do the same for temperature, luminosity, mass, or lifetime: Clicking one of these properties in the list along the right changes the slider to that
property. Note that this interactive figure allows you to vary properties of main­sequence stars only, not of any other type of star (such as giants or white
dwarfs).
Part A
27/29
Mandatory Assignment 3­ testing material from Chaper 15
Compared to a main­sequence star with a short lifetime, a main­sequence star with a long lifetime is __________.
Hint 1. What is the surface temperature of a high­luminosity main­sequence star?
A typical surface temperature for a high­luminosity main­sequence star is __________.
ANSWER:
less than about 10,000 K
between about 10,000 K and 50,000 K
greater than about 50,000 K
Hint 2. What is the mass of a hot main­sequence star?
A typical mass for a main­sequence star with high surface temperature is __________.
ANSWER:
less than about 5 solar masses
between about 5 and 100 solar masses
greater than about 100 solar masses
ANSWER:
more luminous, hotter, larger, and more massive
more luminous, hotter, smaller, and less massive
less luminous, cooler, larger, and more massive
less luminous, cooler, smaller, and less massive
Correct
Note that there are physical reasons why long­lived stars have these properties: They are less luminous because they burn their fuel at a much
lower rate than short­lived stars; they burn it at this lower rate because they are less massive (which means less compression and hence a lower
fusion rate in their cores); and their lower masses lead to their smaller sizes and lower surface temperatures.
Part B
Compared to a high­luminosity main­sequence star, stars in the upper right of the H­R diagram are __________.
Hint 1. Which star is hotter?
Be sure you have clicked on the "show stars" button and then locate Spica (near the top of the main sequence) and Betelgeuse (near the upper
right) in the H­R diagram.
True or False? Spica has a higher surface temperature than Betelgeuse.
ANSWER:
True
False
Hint 2. Which star is larger?
Be sure you have clicked on the "show stars" button and then locate Spica (near the top of the main sequence) and Betelgeuse (near the upper
right) in the H­R diagram.
True or False? Betelgeuse is larger in radius than Spica.
ANSWER:
True
False
ANSWER:
28/29
Mandatory Assignment 3­ testing material from Chaper 15
hotter and larger in radius
cooler and larger in radius
cooler and smaller in radius
hotter and smaller in radius
Correct
Be sure to notice that luminosity increases upward on the diagram, surface temperature increases to the left, and radius increases diagonally from
the lower left to the upper right. Therefore, stars in the upper right must be high in luminosity and radius, but low in surface temperature. These
stars are called giants or supergiants because of their large radii.
Part C
Compared to a low­luminosity main­sequence star, stars in the lower left of the H­R diagram are __________.
Hint 1. Which star is hotter?
Be sure you have clicked on the "show stars" button and then locate Sirius B (near the lower left) and Ross 128 (near the lower right) in the H­R
diagram.
True or False? Sirius B has a higher surface temperature than Ross 128.
ANSWER:
True
False
Hint 2. Which star is larger?
Be sure you have clicked on the "show stars" button and then locate Sirius B (near the lower left) and Ross 128 (near the lower right) in the H­R
diagram.
True or False? Sirus B is larger in radius than Ross 128.
ANSWER:
True
False
ANSWER:
hotter and larger in radius
cooler and larger in radius
cooler and smaller in radius
hotter and smaller in radius
Correct
Notice that the stars in the lower left of the diagram are called white dwarfs: white because they are hot enough to appear “white hot” to our eyes,
and dwarfs because of their small sizes. A typical white dwarf is no larger in size (radius) than our Earth, but has as much mass as the Sun.
29/29