question 4 - portfolio chapter 12 homework https: ... a star's birth mass is the most important...

11/20/2016 Chapter 12 Homework

https://session.masteringastronomy.com/myct/assignmentPrintView?assignmentID=1646896 1/18

Chapter 12 HomeworkDue: 11:59pm on Tuesday, October 25, 2016

To understand how points are awarded, read the Grading Policy for this assignment.

Question 1

Choose the best answer.

Part A

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

ANSWER:

Correct

Question 2

Part A

The total amount of power (in watts, for example) that a star radiates into space is called its _________.

ANSWER:

Correct

Question 3

Part A

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

ANSWER:

Correct

Question 4

the time between eclipses and the average distance between the stars the period of the binary system and its distance from the Sun the velocities of the stars and the Doppler shifts of their absorption lines

absolute magnitude luminosity apparent brightness flux

Its apparent brightness will decrease by a factor of 3.

Its apparent brightness will increase by a factor of 3.

Its apparent brightness will increase by a factor of 9.

Its apparent brightness will decrease by a factor of 9.



Part A

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

ANSWER:

Correct

Question 5

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:

Hint 2. What are mainsequence stars?

ANSWER:

Hint 3. What are white dwarfs?

ANSWER:

ANSWER:

Determine the distance to the star from its apparent brightness. Determine both the star's distance and luminosity from its apparent brightness. Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity. Calculate the star's surface temperature if we know either its luminosity or its distance.

surface temperature only luminosity only radius only both radius and luminosity both surface temperature and luminosity

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

White dwarfs are small and _____.

dim very luminous short lived cool



Correct

Be sure that you understand why each of these characteristics goes with either giants/supergiants, mainsequence stars, or white dwarfs. If you areunsure, review the HR diagram in your textbook.

Question 6

First, launch the animation below. Explore the interactive figure before beginning to answer the questions. Click the “show stars” button to see the mainsequence and then move the “radius” slider (at bottom) to see the location along the main sequence of a mainsequence star with that particular radius. Youcan 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

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:

Hint 2. What is the mass of a hot mainsequence star?

less than about 10,000 K between about 10,000 K and 50,000 K greater than about 50,000 K



A typical mass for a mainsequence star with high surface temperature is __________.

ANSWER:

ANSWER:

CorrectNote that there are physical reasons why longlived stars have these properties: They are less luminous because they burn their fuel at a much lowerrate than shortlived stars; they burn it at this lower rate because they are less massive (which means less compression and hence a lower fusionrate 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 upperright) in the HR diagram.True or False? Spica has a higher surface temperature than Betelgeuse.

ANSWER:

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 upperright) in the HR diagram.True or False? Betelgeuse is larger in radius than Spica.

ANSWER:

ANSWER:

less than about 5 solar masses between about 5 and 100 solar masses greater than about 100 solar masses

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

True False

True False

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 fromthe 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 starsare 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 HRdiagram.True or False? Sirius B has a higher surface temperature than Ross 128.

ANSWER:

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 HRdiagram.True or False? Sirus B is larger in radius than Ross 128.

ANSWER:

ANSWER:

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, anddwarfs 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.

Question 7

Part A

Why is a star's birth mass its most fundamental property?

ANSWER:

True False

True False

hotter and larger in radius cooler and larger in radius cooler and smaller in radius hotter and smaller in radius



Correct

Question 8


Part A

Which of these stars is the most massive?

ANSWER:

Correct

Question 9


Part A

Which of these stars has the longest lifetime?

ANSWER:

Correct

Question 10


Part A

Which of these stars has the largest radius?

ANSWER:

A star's birth mass is the most important predictor of a star's luminosity. A star born with low mass will have a high luminosity; a star born withhigh mass will have a significantly lower luminosity.

A star's birth mass is the most important predictor of a star's surface temperature. A star born with low mass will have a high surfacetemperature; a star born with high mass will have a significantly lower surface temperature.

A star's birth mass is the most important predictor of a star's lifetime. A star born with high mass will have a short lifespan; a star born with lowmass will have a significantly longer lifespan.

A star's birth mass is the most important predictor of a star's size. A star born with high mass will have a small radius; a star born with lowmass will have a significantly greater radius.

a mainsequence star a mainsequence star a mainsequence star

A

G

M

a mainsequence star a mainsequence star a mainsequence star

A

G

M



Correct

Question 11


Part A

Which of these stars has the greatest surface temperature?

ANSWER:

Correct

Question 12

Part A

From hottest to coolest, the order of the spectral types of stars is _________.

ANSWER:

Correct

Question 13

Part A

Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

ANSWER:

a supergiant star a giant star a supergiant star

A

K

M

a 30 mainsequence star

a supergiant star a Cepheid variable star

MSun

A

ABFGKMO OBAGFKM OMKGFBA OBAFGKM ABCDEFG

We know the star's luminosity and distance. The star is of spectral type G. The star is a member of a binary star system. The star is of spectral type A.



Correct

Question 14

Part A

What is the common trait of all main sequence stars?

ANSWER:

Correct

Question 15

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 fewproperties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instrumentssuch 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:

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, themore distant star should appear dimmer by a factor of . But is this necessarily true in all cases?

ANSWER:

Hint 3. What is a parallax angle used for?

If you know a star’s parallax angle, then you can calculate its _____.

ANSWER:

They are all spectral type G. They all have approximately the same mass. They are in the final stage of their lives. They generate energy through hydrogen fusion in their core.

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.

= 100102

Yes. The inverse square law for light is an absolute law that is always valid. 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. 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 4. How do we know the temperature of the Sun’s photosphere?

We learn the temperature of the Sun’s photosphere by __________.

ANSWER:

Hint 5. How do we find the masses of distant objects?

We can calculate the mass of a distant star by __________.

ANSWER:

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:

ANSWER:

radius distance mass

sending space probes that carry thermometers into the photosphere applying the inverse square law for light studying the Sun’s color and spectrum

measuring its parallax angle applying the inverse square law for light applying Newton’s version of Kepler’s third law

calculate it from the star’s luminosity and surface temperature determine it from the star’s parallax angle measure the star’s angular diameter in the sky



Correct

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’ssurface 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 neutralhydrogen atoms, and one has mostly hydrogen ions (and free electrons). Which cloud is the hottest?

ANSWER:

ANSWER:

Correct

A star’s spectral type (OBAFGKM) tells us its surface temperature, because different sets of lines form more easily at different temperatures. Colorcan 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?

the neutral cloud the molecular cloud the ionized cloud

mass parallax angle spectral type apparent brightness



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, themore distant star should appear __________.

ANSWER:

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 theinverse square law for light, then the luminosity you calculate for the street light will be __________.

ANSWER:

ANSWER:

Correct

We can use the inverse square law for light to calculate the star’s luminosity from its apparent brightness and distance. However, this calculatedvalue 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 andthe star, we can sometimes measure the amount and therefore determine the star's luminosity by accounting for the light this dust absorbs orscatters.)

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:

ANSWER:

brighter by a factor of 10 dimmer by a factor of dimmer by a factor of 10

= 100102

too high, because the fog makes the light appear brighter than it really is accurate, because the inverse square law for light is always valid too low, because the fog absorbs some of the light, making the light appear dimmer than it really is

We have measured the star’s spectral type. We have measured the star’s distance. We have measured the star’s apparent brightness. The star must be a member of a binary system. No interstellar gas or dust absorbs or scatters light between us and the star.

Earth’s radius and Earth’s surface atmospheric pressure the Moon’s average distance from Earth and the Moon’s orbital period around Earth Earth’s radius and Earth’s distance from the Sun



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 anorbiting object. This is possible for an eclipsing binary system, because the two stars orbit each other (and the eclipses tell us that we are viewingthe 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 cannotapply 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:

ANSWER:

Correct

All mainsequence stars of a particular spectral type have approximately the same mass. Therefore, if we know the star’s spectral type and knowthat it is a mainsequence star, then we can infer its mass.

Question 16

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:

it is a member of an eclipsing binary system it is near enough for us to measure its distance with parallax it is unusually high in mass we know its spectral type

a mainsequence star located within the Milky Way Galaxy the same age as the Sun

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. We have measured the star’s velocity.

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:

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 orgreen 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 orred star.

ANSWER:

CorrectNotice 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 arethe 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 havethe 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:

shorter wavelength longer wavelength

HelpReset

Lowest temperatureHighest temperature

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:

CorrectAll five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, allfive 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 luminosityfrom highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

ANSWER:

HelpReset


HelpReset

Lowest luminosityHighest luminosity



Correct

Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosityaxis 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 toinvestigate surface temperature and luminosity for a different set of five stars.

Part D




ANSWER:

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 Mhaving the lowest surface temperature. In other words, spectral type increases to the left on the HR diagram. Now proceed to Part E to determinehow 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 fivestars shown in Part D. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

ANSWER:


HelpReset




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 formore practice in reading surface temperature and luminosity on the HR diagram.

Part F




ANSWER:

ANSWER:

HelpReset





Correct

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type Mhaving 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 luminosityfrom highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

ANSWER:

HelpReset


HelpReset




Correct

As always, the HR diagram shows surface temperature along the horizontal axis and luminosity along the vertical axis.

Question 17


Part A

Which of these star clusters is oldest?

ANSWER:

Correct

Question 18

Part A

What do we mean by the mainsequence turnoff point of a star cluster, and what does it tell us?

ANSWER:

Correct

Score Summary:Your score on this assignment is 50.8%.You received 24.4 out of a possible total of 48 points.

a cluster whose brightest mainsequence stars are white a cluster whose brightest mainsequence stars are yellow a cluster containing stars of all colors

It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. It is the mass of the most massive star in the star cluster, and it tells us the cluster's size. It is the point in a star cluster beyond which main sequence stars are not found, and it tells us the cluster's distance. It is the faintest and coldest main sequence star in a cluster, and it tells us the cluster's age.

question 4 - portfolio chapter 12 homework https: ... a star's birth mass is the most important...

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