Astronomy Ch 10 HW
From the figure shown here, what is the absolute magnitude of a Type II Cepheid with a period of 20 days?
-2
A Sense of Proportion: Arrange the following in order from first to last:
Cloud of gas and dust in space, protostar, main sequence star, giant, planetary nubula
Why does a star's life expectancy depend on mass?
Mass determines the amount of fuel a star has for fusion and determines the rate of fuel consumption for a star.
Which is true for main-sequence stars?
Massive stars are bright.
What happens to a star when it becomes a giant if it has a close binary companion?
Matter can be transferred from the giant to the companion.
Why does an expanding giant star become more luminous?
More energy is produced in the interior
Why are lower main-sequence stars more abundant than upper main-sequence stars?
More low-mass main-sequence stars are formed in molecular clouds and lower main-sequence stars have much longer lifetimes than upper main-sequence stars.
With respect to main-sequence stars and stellar evolution, select all of the correct statements from the following list.
More massive stars are hotter and brighter. Stars change position on the main sequence throughout their lives. The weight of a star must be balanced by internal pressure.
Consider the three H-R diagrams of the star clusters shown above: NGC2264, Pleiades, and M67. The youngest cluster is ________ and has ________ -type stars.
NGC4622; pre-main sequence
Why does the surface temperature of an expanding star change?
Since energy on the star's surface is spread out over more area, it gets cooler.
Why does the luminosity of an expanding star change?
Since the star is getting bigger, it has more area through which to give off energy, so it gets brighter.
What evidence do we have that some close binary pairs have merged to become a single giant star?
Some giant stars have rapid rotation.
Based on the deaths of lower-main-sequence stars, select all of the correct statements from the following list.
Some giant stars will lose mass into space and form planetary nebulae. Red dwarfs will live for a very long time. Most stars become white dwarfs. Some stellar cores are too massive to become white dwarfs.
Why will a helium flash never occur in some stars?
Some stars do not develop degenerate helium cores.
With respect to the evolution of star clusters, select all of the correct statements from the following list.
Stars in globular clusters tend to be older than those in open clusters. All stars in a cluster are about the same age. The age of a cluster can be determined by where the stars are leaving the main sequence.
How does the main-sequence lifetime of a star compare to its entire fusion lifetime?
Stars spend about 90% of their fusion lifetimes on the main sequence.
Which of the following statements accurately describe(s) some observed properties of supernovae type Ia and supernovae type II?
Supernovae type II have hydrogen lines in their spectra and supernovae type Ia are more luminous.
How do star clusters confirm that stars are evolving?
The H-R diagram of a star cluster is missing the upper part of the main sequence.
How are the ages of star clusters related to their turnoff points?
The age of a cluster is the life expectancy of stars at its turnoff point and the higher the turnoff point, the older the star cluster.
Suppose that you monitor the apparent brightness of a supernova and notice that 50 days after it reached maximum brightness, it has dimmed by 2 magnitudes. Examine the light curves in this figure. Which type of supernova are you most likely observing?
Type II
Why can't the lowest-mass stars become giants?
They are fully convective and never develop a hydrogen shell fusion zone.
Why can't the lowest-mass stars have the same fate as the sun-like stars?
They are not massive enough to collapse to such a high density.
Why can't the lowest-mass stars become giants?
They are not massive enough to fuse helium
Which is true for the mass and life-expectancy of a star?
They are not the only interrelated factors: temperature must be considered too.
Which is true of giant stars?
They are of very low density
What unusual property do all higher-mass white dwarfs have?
They are smaller than lower-mass white dwarfs.
What is the reason for giant stars having the densities that they do?
They are so large.
Which is true for more massive main-sequence stars?
They live shorter lives than low-mass stars.
Why are lower-mass stars unable to ignite more massive nuclear fuels such as carbon?
They never get hot enough.
As white dwarfs cool, which of the following occurs?
They stay the same size and get dimmer.
Based on the deaths of massive stars, select all of the correct statements from the following list.
Transferring mass to a white dwarf could trigger a type Ia supernova. The Chandrasekhar limit is the maximum mass of a white dwarf. Supernovae leave behind shells of gas. More massive stars have more violent deaths.
Which is the result of mass transfer pushing a white dwarf over the Chandrasekhar limit and its core collapsing, causing all its carbon to fuse at once?
a type Ia supernova
Which is the result of a massive star losing its outer layers in a binary system?
a type Ib supernova
Which of the following observable properties of a main-sequence star is a direct indication of the rate at which energy is produced inside that star?
luminosity
Which of the following is NOT considered in making a simple stellar model?
magnetic field
Of the following, which main-sequence star has a longer life expectancy than the sun?
spectral type K2
This diagram illustrates the interior structure of which of the following
supergiant star
Which type of supernova leaves NO core remnant?
supernova type Ia
What event marks the end of every star's main-sequence life?
the end of hydrogen fusion in the core
What is the helium flash?
the explosion of the core of a star at the beginning of helium fusion
What is the turnoff point of a star cluster?
the location on the H-R diagram where stars are leaving the main sequence
Which "variable" in variable stars confirms that stars evolve?
the period of changes in brightness
What happens to white dwarfs as they age?
their surface temperatures decrease and luminosity decreases
According to the figure shown here, what is the approximate radius of the sun's nuclear fusion zone?
0.30 solar radii
This diagram shows the main-sequence lifetimes of stars with 1, 3, and 15 solar masses. Using this figure, what is the estimated main-sequence lifetime of a spectral type F0 star that has a mass of 1.7 solar masses?
3 billion years
With respect to stellar evolution, select all of the correct statements from the following list.
A changing period in a Cepheid variable means that the size of the star is changing and that the star is therefore evolving . Only stars on the instability strip are variable. The period of some Cepheid variables actually changes. Variable stars are expanding and contracting.
With respect to post main-sequence evolution of stars, select all of the correct statements from the following list.
After exhausting its hydrogen fuel, a main-sequence star will become a very large, low-density star. The cores of main-sequence stars begin to collapse when they exhaust their hydrogen. More massive stars will fuse the helium in their cores into heavier elements. After leaving the main sequence, most stars move to the right on the H-R diagram. Correct
Which is not true about expanding stars?
All of these are true. They become more luminous. They get less dense. They become cooler.
Which of the following is true about red dwarfs?
All of these choices are correct. They never become giants. Helium fusion does not occur in a red dwarf. They never develop a shell of hydrogen fusion. None of the red dwarfs in the universe has grown old enough for fusion to stop.
Which stars have high rates of mass loss due to intense stellar winds?
All of these choices are correct. high-mass stars newly forming stars stars approaching death high-mass and newly forming stars
What observational evidence do we have that stars are losing mass?
All of these choices are correct. the solar wind stellar emission lines at ultraviolet and X-ray wavelengths some absorption lines in the spectra of giant stars are blue shifted the solar wind and stellar emission lines at ultraviolet and X-ray wavelengths
Why does the helium flash make it hard for astronomers to understand the later stages of stellar evolution?
All of these choices are correct. It is a short-lived event. It limits the reliability of mathematical models used to study stellar evolution. It happens deep inside a star.
What is required for carbon fusion to occur in the core of a star?
All of these choices are correct. high temperature high pressure high mass
What causes the helium flash?
All of these choices are correct. the beginning of helium fusion in the core of a star gas pressure in a star becoming independent of temperature the core of a star becoming degenerate
What is the main sequence of the H-R diagram?
All of these choices are correct. where most of the stars are found a group of stars ranging from very massive to very low mass a group of stars ranging from cool and dim to bright and hot
What is "variable" in a variable star?
All of these choices are correct. its brightness the period of changes in brightness its size
Which is evidence that stars lose mass?
All of these choices are evidence. supernovae nova explosions planetary nebulae
A Sense of Proportion: Listed here are descriptions of three star clusters. Arrange them in order from youngest to oldest:
Cluster contains hot blue stars, Cluster contains red gant stars but no hot stars, cluster is composed of dim red stars.
Why does an expanding giant star become cooler?
Energy is absorbed in expanding and lifting the gas.
A Sense of Proportion: Arrange the following in order of increasing energy:
Formation of a planetary nebula, type II supernova, type Ia supernova.
What is the general trend in the ages of the two types of star clusters?
Globular clusters are older than open clusters
The H-R diagram of a star cluster that has many hot, blue, luminous stars will have stars over most of the main sequence and be young in age. What is the reason for this?
Hot, blue, luminous stars do not live long lives
A Sense of Proportion: Arrange the following in order from first to last:
Hydrogen core fusion begins, Hydrogen shell fusion begins, helium core fusion begins, helium shell fusion begins, carbon core fusion begins.
Based on evolving stars in binary systems, select all of the correct statements from the following list.
If mass is being transferred in a binary system, it may be detectable. Mass can be transferred between the stars in a binary system. Lagrangian points are stable points in a two-body system.
Why can't massive stars generate energy from iron fusion?
Iron fusion consumes energy.
Which of the following is true for a brown dwarf?
It does not have hydrogen fusion occurring in the core.
Why can't massive stars generate energy from further fusion once iron has been created?
It has the most tightly bound nucleus.
If a star cluster has many hot, blue, luminous stars which of the following is probably correct?
It is young.
What happens to a star in a close binary system when it becomes a giant?
It loses mass to the other star.
Which is true for the mass-luminosity relationship?
It only applies to main-sequence stars.
Which is true for the H-R diagram of a star cluster that has many hot, blue, luminous stars?
It will have stars over most of the main sequence.
Consider the three H-R diagrams of the star clusters shown above: NGC2264, Pleiades, and M67. The oldest cluster is ________ and has ________ -type stars
M67; red giant
Which is a type of star found on the upper end of the main sequence?
O or B
Why is there an upper mass limit for main-sequence stars of about 100 solar masses?
Objects above this mass fuse hydrogen too rapidly and cannot stay together.
Why is there a lower mass limit of 0.08 solar masses for main-sequence stars?
Objects below this mass are not hot enough to fuse normal hydrogen.
Why have no black dwarfs yet been observed in our galaxy?
Our galaxy is too young for any to have formed.
Why are the stars found inside planetary nebulae only at temperatures above 25,000 K?
Planetary nebulae glow due to the ionization of low density gas by a hot interior star.
Why is there a mass-luminosity relationship?
The brightness of a main-sequence star depends on the rate of fusion in the core, which depends on the mass.
Which is a way that some stars avoid the helium flash?
The core doesn't get hot enough for helium fusion.
Why do old supernova remnants emit X-rays?
The expanding hot gas collides with the interstellar medium
This figure shows the post-main-sequence evolution of different stars on the H-R diagram. When the sun leaves the main sequence to become a giant, what happens to its surface temperature and luminosity?
The luminosity increases and the surface temperature decreases.
The period of a Cepheid variable star and the time of one recent maximum can be used to predict the time of a future maximum. Suppose that you calculate the time of future maximum brightness and then make measurements to observe this maximum. After the correction for Earth's orbital position has been made, you find that the maximum occurred a few minutes later than predicted. What does this tell you about this star?
The star is slowly expanding.
What can happen to the white dwarf in a close binary system when it accretes matter from the companion giant star?
The white dwarf can ignite the new matter and flare up as a nova and accrete too much matter and detonate as a supernova type Ia.
Why have no black dwarfs been observed in our galaxy?
There has not been enough time for these objects to form.
Why do white dwarfs have masses approximately equal to the sun?
White dwarfs are the cores of stars that could fuse helium but could not fuse carbon, so they should all be similar mass.
Which spectra contain hydrogen lines?
a type II supernova
Where is mass transfer likely to occur?
a binary system
Which is the result of the accumulation of mass in a close binary system igniting the core of a white dwarf?
a nova explosion
Which is the result of a collapsing iron core in a massive star?
a type II supernova
The density of the sun is about 1.4 grams per cubic centimeter. Density is mass divided by volume. The volume of a sphere is proportional to the radius cubed. According to this graph, what is the density of a one-solar-mass spherical white dwarf?
about 3,000,000 grams per cubic centimeter
How much longer will the sun last?
about 5 billion years
What is the approximate mass for white dwarfs?
about a solar mass
What type of spectrum does the gas in a planetary nebula produce?
an emission line spectrum
What is the probable next step in a star's evolution after the white dwarf stage?
black dwarf
How can you estimate the age of a star cluster?
by its brightest stars
How do star clusters confirm that stars evolve?
by the more massive, brighter stars leaving the main sequence
What prevents gravity from shrinking a white dwarf to a smaller size?
degenerate electrons
What kind of spectrum does a planetary nebula produce?
emission
Which of the following trends accurately represents the characteristics of the several different fusion zones inside a late-stage high-mass star going from the outer to innermost zone?
emperature decreases and mass of individual nuclei increases
Where does a planetary nebula get its energy to produce a spectrum?
from the white dwarf at its center
The plot above shows changes in the observed time minus the predicted time of maximum brightness for a Cepheid variable observed over about a century. This happens because the star is _________ because it _________ time.
getting larger; evolves over
A typical open cluster contains 850 stars and is 27 pc in diameter. A typical globular cluster contains 1 million stars and is 25 pc in diameter. The average distance between stars will be smaller in which type of cluster?
globular
What increases the temperature of an inert helium core inside a giant star?
gravitational contraction
Which type of star eventually develops several concentric zones of active shell fusion?
high-mass stars
What is the heaviest element that can be fused in the core of a star?
iron
How many black dwarfs have been observed in our galaxy?
none
Which is a type of star found on the lower end of the main sequence?
red dwarf
Ultimately a sun-like star will become which of the following?
white dwarf
