Download Oct 06, 2001

1)
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.
Spectral Type
O5
10,000
B5
A5
K5
M5
Red Giants
a
d
1,000
Luminosity (solar units)
F5 G5
-5
b
100
10
1
0
Main
Sequence
e
5
.1
.01
f
10
Absolute magnitude
2) 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.
c
3) Which statement is the most correct
.001
White
Dwarfs
about the comparison between a K5
.0001
15
main sequence star and a B5 main
sequence star?
20,000
10,000
5,000
A) The K5 star is cooler, less
Temperature (K)
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.
4) 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.
5) 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 10,000 K
6) When a star like the sun evolves into a red giant, its core
A) expands and cools.
C) expands and heats.
B) contracts and heats.
D) contracts and cools.
7) 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.
8) 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.
9) 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
10) At the end of a Main Sequence O star’s evolution its core is composed primarily of
A) Hydrogen
C) Carbon
E) Uranium
B) Helium
D) Iron
11) 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
E) There is insufficient information to
answer this question.
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
1
1.2
1.4
0.2
0.4
0.6
0.8
1
1.2
1.4
B-V
B-V
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 has a large number of stars that are producing energy by core Heburning?
A) Star Cluster A
C) Star Cluster C
B) Star Cluster B
D) Star Cluster D
32) 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.
Refer to H-R diagram illustrating the
evolutionary track of a 1 solar mass star to the
right to answer the following 5 questions
33) 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
e
-10
d
-5
0
M
+5
b
c
a
+10
+15
+20
O
34) Which of the methods of energy
production is at active along the portion
of the track marked (d)?
A) Core H-burning
C) Shell H-burning
B) Core He-burning
D) Shell He-burning
B A
F G
K
M
E) Proton-proton chain
35) At which of the lettered positions on the H-R diagram (a) through (e) will the star spend the
most time?
36) 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.
37) Along the track marked (e) the core of the star is composed of
A) Hydrogen
C) Carbon
B) Helium
D) Iron
E) Uranium
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) The spectrum of the star designated HD 20899 is shown below. Ignore the many
absorption lines and use the bold smoothed spectrum to answer the following
question. Is this star hotter or cooler than the Sun? Estimate λMax from the spectrum
and then use Wien’s law to estimate the temperature of the star. Don’t forget to
answer the original question.
375
400
425
Wavelength, nm
450
475
2) A star is known to be half the temperature of the Sun and twice its radius. What is its
luminosity? You may answer either in Watts or in units of solar luminosity.