Chapter 10 Flashcards
With respect to main-sequence stars and stellar evolution, select all of the correct statements from the following list.
Since the interiors of stars cannot be observed, there are no theories about their structure.
More massive stars live longer; they take longer to use up all their energy.
Energy flow in a star is a balance between what comes in and what goes out.
Stars change position on the main sequence throughout their lives.
Outward energy flow in a star is by conduction only.
More massive stars are hotter and brighter.
The weight of a star must be balanced by internal pressure.
Stars change position on the main sequence throughout their lives.
Outward energy flow in a star is by conduction only.
More massive stars are hotter and brighter.
The weight of a star must be balanced by internal pressure.
With respect to post main-sequence evolution of stars, select all of the correct statements from the following list.
Moving to the right on the H-R diagram indicates only that the star has cooled, nothing else.
The cores of main-sequence stars begin to collapse when they exhaust their hydrogen.
After leaving the main sequence, most stars move to the right on the H-R diagram.
The helium flash causes a red giant star to go supernova.
More massive stars will fuse the helium in their cores into heavier elements.
Because of the core contraction, the temperature of a star will increase when the hydrogen fuel is exhausted.
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.
After leaving the main sequence, most stars move to the right on the H-R diagram.
More massive stars will fuse the helium in their cores into heavier elements.
After exhausting its hydrogen fuel, a main-sequence star will become a very large, low-density star.
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.
The turnoff point is when stars in a cluster begin to no longer shine.
All stars in a cluster are about the same age.
Stars in globular clusters tend to be helium-poor.
Open clusters have more stars than globular clusters.
The age of a cluster can be determined by where the stars are leaving the main sequence.
The less massive stars in a cluster leave the main sequence first.
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.
With respect to stellar evolution, select all of the correct statements from the following list.
Variable stars are expanding and contracting.
The period of some Cepheid variables actually changes.
More massive stars will vary their brightness more quickly.
When getting dimmer, variable stars are releasing energy; when getting brighter they are storing energy.
Despite their variability, variable stars stay in a specific position on the H-R diagram.
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.
Variable stars are expanding and contracting.
The period of some Cepheid variables actually changes.
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.
In the model shown above, what fraction of the sun’s mass is hotter than 3,000,000 K?
0.97
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
Which of the following is NOT considered in making a simple stellar model?
magnetic field
According to the figure shown here, what is the approximate radius of the sun’s nuclear fusion zone?
0.30 solar radii
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 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.
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
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.
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 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
Why does an expanding giant star become cooler?
Energy is absorbed in expanding and lifting the gas.
Of the following, which main-sequence star has a longer life expectancy than the sun?
spectral type K2
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.
Why does an expanding giant star become more luminous?
More energy is produced in the interior.
What increases the temperature of an inert helium core inside a giant star?
gravitational contraction
How much longer will the sun last?
about 5 billion years
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.
Why will a helium flash never occur in some stars?
Some stars do not develop degenerate helium cores.
Why are lower-mass stars unable to ignite more massive nuclear fuels such as carbon?
They never get hot enough.
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.
What is the general trend in the ages of the two types of star clusters?
Globular clusters are older than open clusters.
From the figure shown here, what is the absolute magnitude of a Type II Cepheid with a period of 20 days?
–2
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 is the main sequence of the H-R diagram?
All of these choices are correct.
Which is a type of star found on the lower end of the main sequence?
red dwarf
Which is a type of star found on the upper end of the main sequence?
O or B
Which of the following is true for a brown dwarf?
It does not have hydrogen fusion occurring in the core.
Which is true for the mass-luminosity relationship?
It only applies to main-sequence stars.
Which is true for main-sequence stars?
Massive stars are bright.
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 true for more massive main-sequence stars?
They live shorter lives than low-mass stars.
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 not true about expanding stars?
All of these are true.
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 is the helium flash?
the explosion of the core of a star at the beginning of helium fusion
What causes the helium flash?
All of these choices are correct.
Why does the helium flash make it hard for astronomers to understand the later stages of stellar evolution?
All of these choices are correct.
Which is a way that some stars avoid the helium flash?
The core doesn’t get hot enough for helium fusion.
Which is true of giant stars?
They are of very low density.
What is the reason for giant stars having the densities that they do?
They are so large.
