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(PHYS002)sol2a_f03.pdf
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Physics 002 Midterm 2 18 November, 2003.
Time allowed: 70 minutes Total: 70 marks
Name: Solution
Student ID:
Seat:
A
Table 1: Useful Data
Suns temperature
5,800 K
Suns absolute magnitude
+4.8
1 AU
1.5 108 km
Table 2: Spectral Types and Temperatures of Stars
Spectral type
O5
B0
B5
A0
A5
F0
F5
Temperature (K)
40,000
28,000
15,000
9,900
8,500
7,400
6,600
Spectral type
G0
G5
K0
K5
M0
M5
M8
Temperature (K)
6,000
5,500
4,900
4,100
3,500
2,800
2,400
Figure 1: HR Diagram with Luminosity Classes
Section A: Short Questions (8 marks)
For each astronomical object described in (1-8), identify the approximate locations (P, Q, R, U, V, W, X, Y, Z) in the following HR diagram in Figure 2:
Figure 2: HR Diagram for identification of astronomical objects
Astronomical object
Location
(1)
The protostar of a K0 main-sequence star.
W
(2)
A main-sequence star with a convective zone in the core.
P
(3)
A main-sequence star which will undergo a post-main-sequence evolution with a helium flash.
V
(4)
A main-sequence star which fuses hydrogen by a CNO cycle.
P
(5)
A star with a pulsating layer of partially ionized helium in its outer envelope.
Q
(6)
The end product of a star which dies after it stops burning hydrogen and helium, with no ignition of heavier elements.
Y
(7)
A main-sequence star which will die by shedding its envelope in the form of a planetary nebula.
V
(8)
A main-sequence star which will never become a giant star.
Z
Section B: True and false (14 marks)
Yes
No
(1)
Emission nebulae are pink because the blackbody radiation spectra of the stars in the nebulae are pink.
(2)
Visible light images of dense clouds reveal that young stars are formed inside the clouds.
(3)
Due to its strong stellar wind, the formation of a luminous massive star prevents the formation of other stars around it.
(4)
The process of star formation from interstellar clouds is shorter for massive stars than lighter ones.
(5)
Cepheid variable stars can be used as distance indicators because their pulsating periods are correlated with their luminosities.
(6)
Planetary nebulae can be used as distance indicators because their sizes are proportional to their age.
(7)
Scientists on Earth can detect positrons, neutrinos and gamma rays produced in the nuclear fusion of a main-sequence star.
U
V
W
X
Y
(1) Emission nebulae are pink