Download Oct 06, 2001

Sample Exam Questions
Answer all questions on the exam in the provided spaces. Use the Scantron
answer sheet to record your answers.
Refer to these stars in the table below in answering the following questions. There may be more
than one correct answer to some of the following questions. Choose all that apply.
Spectral
Luminosity
Star
m
M
Type
Class
A
-0.3
-0.3
K2
III
B
1.36
-6.8
O9
I
C
1.29
-5.2
A2
II
D
11.05 15.5
M5
V
E
0.91
-3.6
B1
V
1. Which of the stars listed above is appears the dimmest?
2. Which of the stars listed above is the most luminous?
3. Which of the stars listed above is the hottest?
4. Which of the stars listed above is the largest in radius?
5. Which of the stars listed above is the closest?
6. Which of the stars listed above is 10 parsecs away?
7. Which of the stars listed above is a main sequence star?
8. Which of the two stars D or E is closer?
9. Which of the stars listed above has the longest remaining lifetime?
10. Which of the stars listed above has a spectral type different from its original spectral type?
11. A star leaves the main sequence when
A. nuclear fuel in its core can supply enough energy to stop its collapse.
B. it collapses, and its envelope becomes degenerate.
C. it stops fusing hydrogen in its core and starts to expand.
D. it forms planets.
The HR Diagram at right is provided to assist with answering the following two questions.
12. Which is hotter, a main
sequence star with an
absolute magnitude of M=
4 or a white dwarf with a
luminosity 100 times
smaller than the Sun?
A. the main sequence star
B. the white dwarf
C. They have the same
temperature.
D. There is insufficient
information to
determine this.
α
β
γ
13. Which of the statements
below is true regarding the
two stars marked α and β?
A. Star α is hotter than star β.
B. Star α is less luminous than star β.
C. Star α is larger in radius than star β.
D. Star α appears brighter that star β.
14. Which of the statements below is true regarding the two stars marked α and γ?
A. Star α is less luminous than star γ.
B. Star α has a longer main sequence lifetime than star γ.
C. Star α appears brighter that star γ.
D. Star α is larger in radius than star γ.
15. Which statement is the most correct about the comparison between a K5 main sequence star and
a B5 main sequence star?
A. The K5 star is cooler, less luminous, smaller, and will not live as long as the B5 main
sequence star.
B. The K5 star is hotter, less luminous, larger, and will live longer than the B5 main sequence
star.
C. The K5 star is smaller, hotter, more luminous, and will not live as long as the B5 main
sequence star.
D. The K5 star is hotter, more luminous, smaller, and will live longer than the B5 main
sequence star.
E. The K5 star is less luminous, cooler, smaller, and will live longer than the B5 main
sequence star.
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16. Fragments of Giant Molecular Clouds that proceed on to form stars are called protostars. These
protostars heat up even though conditions in their cores are not sufficient to begin nuclear
fusion. What causes these protostars to heat up?
A. The energy they absorb from nearby hot stars.
B. Gravitational energy released from the gas and dust as the fragment collapses.
C. Fusion of hydrogen into helium in the envelope of these protostars.
D. Energy released from their magnetic fields.
17. Four main sequence stars are described below. Which will have the shortest main sequence
lifetime?
A. A main sequence star of 50 solar
C. A main sequence star that is yellow in
masses.
color
B. A main sequence star that is 0.1 solar
D. A main sequence star with a surface
radii in size.
temperature of 6,000 K
18. What is a “planetary nebula”?
A. It is the disk of gas around a young star.
B. It is the cloud from which protostars form
C. It is a shell of gas ejected from a star late in its life.
D. It is what is left when a white dwarf star explodes as a supernova.
19. What makes a high-mass star's core collapse?
A. Energy from its outer layers compresses its core.
B. The only thing that can make a star's core collapse is a collision with another star
C. Massive stars develop iron cores that cannot fuse anymore, so the core collapses under the
force of its own gravity.
D. Massive stars' cores don't collapse. They expand and become planetary nebulas.
20. A Main Sequence O star will have a main sequence lifetime of about
A. 100 Byrs
C. 1 Byrs
B. 10 Byrs
D. 100 Myrs
E. 1 Myrs
21. At the end of a Main Sequence O star’s evolution, just before its final demise, its core is
composed primarily of
A. Hydrogen
C. Carbon
E. Uranium
B. Helium
D. Iron
22. A 10th magnitude star is ____ than a 5th magnitude star.
A. 2 times brighter
C. 100 times brighter
B. 2 times fainter
D. 100 times fainter
This is a” thinking” question: Star A appears brighter than Star B, but Star A actually gives off
less energy than Star B. The apparent magnitude and absolute magnitudes for Star A are m = 1
and M = -2, respectively. Use this information to answer the following two questions.
23. Which of the following are the best possible values for the apparent and absolute magnitudes of
Star B?
A. m = -1 and M = 2
C. m = 3 and M = 2
B. m = -1 and M = -4
D. m = 3 and M = -4
24. Which is the most correct statement about the distance of Star A from Earth?
A. Star A is closer than 10 pc from Earth.
B. Star A is exactly 10 pc from Earth.
C. Star A is farther than 10 pc from Earth.
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25. Which of the following lists, in the correct order, a possible evolutionary path for a star?
A. Red Giant, Neutron Star, White Dwarf, Nothing
B. Red Giant, Type I Supernova, Black Hole
C. Red Giant, Type II Supernova, Planetary Nebula, Neutron Star
D. Red Giant, Planetary Nebula, White Dwarf
E. Red Giant, Planetary Nebula, Black Hole
26. If the stars Betelgeuse and Rigel were to have the same luminosity but the temperature of
Betelgeuse is cooler than Rigel, which star has the greater surface area?
A. Betelgeuse
B. Rigel
C. They are the same size.
D. There is insufficient information to answer this question.
27. Proxima Centauri is a main sequence star that appears red when viewed from Earth, as a result
which of the following are true:
A. It is hotter than an O spectral class main sequence star.
B. It is moving toward the Earth.
C. It is moving away from the Earth.
D. It will live longer than a B spectral class main sequence star.
E. It is the same size as a red giant star of the same temperature.
28. There are reported to be about 6,000 stars visible to the naked eye. How many of those stars
would you expect to be part of a multiple star system?
A. None
B. 100
C. 1,000
D. 3,000
E. 5,000
Imagine you are comparing the five stars (A-E, shown below) of different radii and temperatures.
The temperature of each star is indicated by a shade of gray (as shown at right), such that the lighter
the shade of gray, the higher the temperature of the star.
High
Medium
A
B
C
D
Low
E
29. Which of the following is the most correct ranking for the luminosity of these stars from
greatest to least?
A. C > E > A >B > D
B. D > B > A >E > C
C. C > E > B >A > D
D. E > C> A >B > D
E. C = E > A =B > D
Use the four HR diagrams shown below to answer the following two questions.
Star Pleiades
Cluster A
Star MCluster
B
67
6
8
8
10
10
V
12
V
12
14
14
16
16
18
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
18
2
0
B-V
0.2
Star Cluster
C
M3
0.4
0.6
0.8
1
B-V
1.2
1.4
1.6
1.8
2
Star Cluster
D
M35
8
13
14
10
15
16
12
V
V
17
14
18
19
16
20
21
18
0
22
0
0.2
0.4
0.6
0.8
B-V
1
1.2
1.4
0.2
0.4
0.6
0.8
B-V
1
1.2
1.4
30. Which of the following is the most correct ranking for the age of the star clusters from youngest
to oldest?
A. A<B<C<D
C. C<B<A<D
B. D<C<A<B
D. D<A<B<C
31. Which of the star clusters in the HR diagrams has a large number of stars that are producing
energy by core He-burning?
A. Star Cluster A
C. Star Cluster C
B. Star Cluster B
D. Star Cluster D
Refer to H-R diagram illustrating the evolutionary track of a 1 solar mass star to the right to
e
answer the following 5 questions
32. Which of the objects listed below
would be observed along the portion of
the track marked (e)?
A. White dwarf
B. Planetary Nebula
C. Red Giant
D. Horizontal Branch star
E. None of the above
33. Which of the methods of energy
production is at active along the portion
of the track marked (d)?
A. Core H-burning
B. Core He-burning
C. Shell H-burning
D. Shell He-burning
E. Proton-proton chain
-10
d
-5
0
M
b
c
+5
a
+10
+15
+20
O
B A
F G
K
M
34. At which of the lettered positions on the H-R diagram (a) through (e) will the star spend the
most time?
35. Which of the following processes is responsible for the evolution along the track marked (b)?
A. The star’s core has exhausted its energy supply and the star is shrinking and cooling.
B. The core is expanding and raising the stars temperature and radius.
C. The core has stopped producing energy and shell of energy production around the
collapsing core is causing the star to increase in radius.
D. The core is now all iron and the star is about to supernova.
36. Along the track marked (e) the core of the star is composed of
A. Hydrogen
C. Carbon
B. Helium
D. Iron
E. Uranium
Essay Questions
1. Describe in detail how main sequence stars (like the Sun) produce energy. Use the
Sun as an example. Be as detailed as you possible. (10 points)
2. You may have heard it said that the Sun is a “typical” star. Please make an
argument below to either support or refute this statement citing specific
characteristics of the Sun, the Bright Stars in the night sky and the most common
stars. (10 points)
Please solve the following two numerical problems. Clearly show how you have arrived
at your result. The points awarded will be based on how clearly you have demonstrated
good problem solving practices. Three points each.
1) An O star is known to be ten times the temperature of the Sun and six times its
radius. What is its luminosity? You may answer either in Watts or in units of
solar luminosity. Note: the radius of the Sun is 696,000 km and the temperature
of the Sun is 5,800 K.
2) What is the average density of an M main sequence star given that it has a radius
of 7.0 x 109 cm and a mass of 2.0 x 1032 grams.
Physical Constants and Formulas
t
d
v
4
VSphere  R 3
3
GM
vOrbital 
R
2GM
R

A
L


2D
360
v Escape 
M
D (parsecs) 
4 2 r 3

G P2
Density 
1
p (arcsecond s)
Mass
M

Volume 4 3
R
3
M
years, where M and L are in solar units.
L
Stephan Boltzmann Law L  4R 2  T 4
Main Sequence Lifetime T  1010 
Wien' s Law T (K) 
3 10 6
Max nm 