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ch 20 Learning curve

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Where would you look to find Population II stars?
in globular clusters
The region of the Hertzsprung-Russell diagram occupied by stars that pulsate with periods between a few days and a few weeks
extends from above the middle of the main sequence toward high-luminosity, low-temperature regions.
If you were to select a star at random within the Milky Way Galaxy, changes are very great that it would be a ____ dwarf.
red
As a star evolves off the main sequence, its position on the Hertzsprung-Russell moves toward the
upper right
In a binary star system with components of unequal masses,
the larger Roche lobe surrounds the more massive star.
The main difference in the energy generation mechanism between a solar mass main-sequence star and one of less than 0.4 solar masses is the lower-mass star convects throughout its whole volume rather than just in its _____ layers.
outer
Compared with Population I stars, Population II stars have
fewer metals
A semidetached binary is a binary star system in which
one star fills its Roche lobe.
A Cepheid variable pulsates because compressing ______ in its atmosphere causes this gas to ionize and becoming opaque, thus trapping heat which later causes the star to expand.
helium
An alpha (α) particle is
the nucleus of a helium atom.
The spectrum of a Population II star is characterized by _____ metal lines.
weak
The _____ strip is where evolving stars pulsate.
instability
A star first leaves the main sequence when it starts burning ____ the core.
hydrogen in a shell around
If the Hertzsprung-Russell diagram of all the stars in a cluster is plotted as the cluster evolves, the main sequence
becomes progressively shorter as high-mass stars exhaust all the hydrogen in their cores and evolve away from the upper blue end.
A semidetached binary is a binary star system in which one star fills its _____ lobe.
ROCHE
A Cepheid variable pulsates because compressing ______ in its atmosphere causes this gas to ionize and becoming opaque, thus trapping heat which later causes the star to expand.
helium
To find Population II stars, you should look in _____ clusters.
globular
An alpha (α) particle is the _____ of a helium atom.
nucleus
When the Sun completes its life on the main sequence about six billion years from now, its position on the H-R diagram will move in the direction toward _____ stars.
red giant
In a binary system if one star alone fills its Roche lobe, the system is a(n) ________ binary.
semi detached
Of the following methods, which is the most accurate for measuring the age of a star cluster?
determining the turn-off point from the main sequence in the Hertzsprung- Russell diagram of the cluster
A Cepheid variable pulsates because compressing ______ in its atmosphere causes this gas to ionize and becoming opaque, thus trapping heat which later causes the star to expand.
helium
Helium fusion begins in the core of a low-mass star after the helium flash. Where did this helium come from?
It was produced by hydrogen fusion during the main sequence phase.
How does the turn-off point on the H-R diagram of a young cluster compare with that for an old cluster? The turn-off point for a young cluster is farther
up the main sequence at hotter spectral types.
More than any other mechanism, the transfer of matter to or from its _____ star affects the evolution of a star that is a member of a close binary system.
companion
The main source of energy in the core of a star that has passed the end of its main-sequence lifetime and is starting to approach the red giant phase is _____ energy, released by the contraction of the hydrogen-poor but helium-rich gas.
gravitational
As a solar mass star expands to become a red giant, its surface temperature of a solar mass star decreases. What is the main reason?
Shell hydrogen fusion generates increased amounts of energy. This generation of energy causes the outer layers of the star to expand, and they cool as they expand.
We know that a globular cluster is old by
examining the H-R diagram for the cluster.
In a β (beta) Lyrae binary star system, the more massive star is the dimmer of the two. This is because the more massive star is hidden by an _____ disc of material from the less massive star.
acceleration
Which one of the following statements correctly describes the difference between a 3-solar-mass pre-main-sequence star (just after it has formed) and a 3-solar-mass red giant star?
The pre-main-sequence star has a uniform composition of mostly hydrogen, whereas the red giant has a hydrogen-rich envelope around a helium-rich core.
One of the most accurate ways of measuring the age of a star cluster is to determine the turn-off point from the _____ in the Hertzsprung- Russell diagram of the cluster.
main sequence
The most important parameter of a star that governs its lifetime is its ____
mass
Most of the stars we see are main-sequence stars, and only about 1% are red giants. This tells us that the main-sequence stage of stellar evolution is about ____ times longer than the red giant stage.
100 x
_____ variables are high mass stars that pulsate regularly in size, brightness, and temperature.
Cepheid
In a post-main-sequence star with about 1 solar mass whose core is shrinking, what physical process will set a definite limit on further compression of the gas in the core by the force of gravity?
quantum mechanical behavior of the free electrons, which prevents their crowding together and generates an outward degeneracy pressure
____ stars are metal-poor stars that are undergoing core helium fusion and pulsate with periods of less than one day.
RR lyrae
The _____ strip is where evolving stars pulsate.
instability
The most important parameter of a star that governs its lifetime is its
mass
How does the turn-off point on the H-R diagram of a young cluster compare with that for an old cluster? The turn-off point for a young cluster is farther up the _____ at hotter spectral types.
main sequence
The helium ____ occurs at the beginning of core helium nuclear reactions in a low-mass star.
flash
Why are horizontal branch stars blue?
After the helium flash in these low-mass stars, energy is generated by both core helium fusion and shell hydrogen fusion. The outer layers are heated as they contract and begin to radiate in the short-wavelength end of the spectrum.
The region of the Hertzsprung-Russell diagram occupied by stars that pulsate with periods between a few days and a few weeks
extends from above the middle of the main sequence toward high-luminosity, low-temperature regions.
When the Sun completes its life on the main sequence about six billion years from now, its position on the H-R diagram will move in the direction toward _____ stars.
red giant
To find Population II stars, you should look in _____ clusters.
globular
How does the turn-off point on the H-R diagram of a young cluster compare with that for an old cluster? The turn-off point for a young cluster is farther up the _____ at hotter spectral types
main sequence