Download PHYS 2410 General Astronomy Homework 7

PHYS 2410 General Astronomy Homework 7
Due 12/02 before the classes
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Multiple Choice (單選題, 33 題, 每題 3 分, 送 1 分)
1.
In the core of a main sequence star, gas pressure _____ the weight of the overlying materials.
a.
is less than
b.
is greater than
*
c.
balances
2.
The energy emitted from the surface of a main sequence star is _____the energy generated in the
core.
a.
greater than
b.
less than
*
c.
equal to
3.
There is a mass-luminosity relation because
*
4.
a.
hydrogen fusion produces helium.
b.
stars expand when they become giants.
c.
stars support their weight by making energy.
d.
the helium flash occurs in degenerate matter.
e.
all stars on the main sequence have about the same radius.
The main sequence has a limit at the lower end because
a.
low mass stars form from the interstellar medium very rarely.
b.
hydrogen fusion combined 4 hydrogen nuclei to form 1 helium nucleus.
c.
pressure does not depend on temperature in degenerate matter.
d.
the lower limit represents when the radius of the star would be zero.
*
e.
there is a minimum temperature for hydrogen fusion.
5.
The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
*
a.
1 M.
b.
60 M .
c.
0.5 M.
d.
0.08 M.
e.
0.001 M.

6.
*
7.
*
8.
In degenerate matter
a.
pressure depends only on the temperature.
b.
temperature depends only on density.
c.
pressure does not depend on temperature.
d.
pressure does not depend on density.
e.
b and c
Giant and supergiant stars are rare because
a.
they do not form as often as main sequence stars.
b
the giant and supergiant stage is unstable.
c.
the giant and supergiant stage is very short.
d.
helium is very rare.
e.
helium flash destroys many of the stars before they can become giants and supergiants.
Which of the following nuclear fuels does a one solar mass star use over the course of its entire
evolution?
*
9.
*
a.
hydrogen
b.
hydrogen and helium
c.
hydrogen, helium, and carbon
d.
hydrogen, helium, carbon, and neon
e.
hydrogen, helium, carbon, neon, and oxygen
What is the approximate age of the star cluster in the diagram below?
a.
2 million years
b.
2 billion years
c.
10 billion years
d.
100 billion years
e.
Apparent
Magnitude
The age of the cluster cannot be estimated from an
HR diagram of the cluster.
O
B
A
F
Spectral Type
10. Star cluster are important to our study of stars because
*
a.
all stars formed in star clusters.
b.
the sun was once a member of a globular cluster.
c.
they give us a method to test the our theories and models of stellar evolution.
d.
they are the only objects that contain Cepheid variables.
e.
all of the above
G
K
M
11. A Cepheid variable with a mass of 10 M ________________ than a Cepheid of 3 M.
*
a.
is less luminous
b.
has a greater surface temperature
c.
has a smaller radius
d.
has a longer period
e.
a and c
12. If the stars at the turnoff point of a cluster have a mass of 3 M, what is the age of the cluster?
(Reference: page 11 of Chap 12 powerpoint file)
*
13.
*
a.
3.01010 years
b.
3.3109 years
c.
6.4108 years
d.
1.61011 years
e.
The age of a star cluster can not be determined from the mass of stars at the turnoff point.
What must occur for an object to be considered a main sequence star?
a.
Hydrostatic equilibrium
b.
Nuclear fusion reaction in the core
c.
Protostar life begins
d.
Both a and b.
14. Why do higher mass stars live shorter lives on the main sequence than lower mass stars?
*
a.
Higher mass stars burn through their nuclear fuel faster.
b.
Lowe
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s
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t
a
r
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tg
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tt
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e
i
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r
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h
a
ts
a
men
u
c
l
e
a
rf
u
s
i
ons
ou
r
c
ea
sh
i
gh
e
rma
s
s
stars.
c.
Higher mass stars have less hydrogen fuel to burn.
d.
Lower mass stars spend a longer time evolving to the main-sequence.
e.
All of the above are false.
15. What characteristic of a star primarily determines its location on the main sequence?
*
a.
age
b.
distance from the galactic center
c.
mass
d.
space motion
e.
radius
16. The lowest-mass stars cannot become giants because
a.
they do not contain helium.
*
b.
they rotate too slowly.
c.
they cannot heat their centers hot enough.
d.
they contain strong magnetic fields.
e.
they never use up their hydrogen.
17. A planetary nebula is
*
a.
the expelled outer envelope of a medium mass star.
b.
produced by a supernova explosion.
c.
produced by a nova explosion.
d.
a nebula within which planets are forming.
e.
a cloud of hot gas surrounding a planet.
18. A white dwarf is composed of
*
a.
hydrogen nuclei and degenerate electrons.
b.
helium nuclei and normal electrons.
c.
carbon and oxygen nuclei and degenerate electrons.
d.
degenerate iron nuclei.
e.
a helium burning core and a hydrogen burning shell.
19. A planetary nebula
*
a.
produces an absorption spectrum.
b.
produces an emission spectrum.
c.
is contracting to form planets.
d.
is contracting to form the star.
e.
is the result of carbon detonation in a 1 M.
20. We know that the central object in a planetary nebula has a surface temperature of at least
_________ because the nebula contains large amounts of ionized hydrogen.
*
a.
5000 K
b.
10,000 K
c.
15,000 K
d.
20,000 K
e.
25,000 K
21. Suppose that a planetary nebula is 0.5 parsecs(=pc) in diameter and expanding at 20 km/s.
old is it?
*
a.
25,000 years
b.
12,000 years
How
c.
6,000 years
d.
49,000 years
e.
100,000 years
22. The Chandrasekhar limit tells us that
*
a.
accretion disks can grow hot through friction.
b.
neutron stars of more than 3 solar masses are not stable.
c.
white dwarfs must contain more than 1.4 solar masses.
d.
not all stars will end up as white dwarfs.
e.
stars with a mass less than 0.5 solar masses will not go through helium flash.
23. A main sequence star of 8.5 solar masses can become a white dwarf by
*
a.
exceeding the Chandrasekhar limit.
b.
losing mass.
c.
gaining mass.
d.
remaining at 8.5 solar masses.
24. The Chandrasekhar limit is ________ solar masses.
*
a.
0.014
b.
0.14
c.
1.4
d.
14
25. The energy a white dwarf emits into space is
*
a.
replaced by fusion of hydrogen atoms into helium.
b.
replaced by fusion of helium atoms into carbon.
c.
not replaced.
26. A Type I supernova is believed to occur when
*
a.
the core of a massive star collapses.
b.
carbon detonation occurs.
c.
a white dwarf exceeds the Chandrasekhar limit.
d.
the cores of massive stars collapse.
e.
neutrinos in a massive star become degenerate and form a shock wave that explodes the
star.
27. A nova is almost always associated with
a.
a very massive star.
*
b.
a very young star.
c.
a star undergoing helium flash.
d.
a white dwarf in a close binary system.
e.
a solar like star that has exhausted its hydrogen and helium.
28. If the theory that novae occur in close binary systems is correct, then novae should
*
a.
produce synchrotron radiation.
b.
occur in regions of star formation.
c.
not occur in old star clusters.
d.
all be visual binaries.
e.
repeat after some interval.
29. Massive stars cannot generate energy through iron fusion because
*
a.
iron fusion requires very high density.
b.
stars contain very little iron.
c.
no star can get hot enough for iron fusion.
d.
iron is the most tightly bound of all nuclei.
e.
massive stars supernova before they create an iron core.
30. Synchrotron radiation is produced by
*
a.
objects with temperatures below 10,000 K.
b.
high-velocity electrons moving through a magnetic field.
c.
cold hydrogen atoms in space.
d.
the collapsing cores of massive stars.
e.
helium flash.
31. A type-II supernova
*
a.
occurs when a white dwarf's mass exceeds the Chandrasekhar limit.
b.
is the result of helium flash.
c.
is characterized by a spectrum that shows hydrogen lines.
d.
occurs when the iron core of a massive star collapses.
e.
c and d
32. What are the two longest stages in the life of a one solar mass star?
a.
Protostar, pre-main sequence.
b.
Protostar, white dwarf.
c.
Protostar, main-sequence.
*
d.
Main-sequence, white dwarf.
33. After what evolutionary stage does a star become a white dwarf?
*
a.
Protostar
b.
Pre-main sequence
c.
Main sequence
d.
Giant