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Physics 002 Midterm 2
Total: 80 marks
20 November, 2001.
Time allowed: 75 minutes
A




Figure 1: HR Diagram with Luminosity Classes


















Figure 2: Period-luminosity Relation for Cepheid Variables






















Table 1: Useful Data about the Sun

1 AU
1.5 108 km

Suns temperature
5,800 K

Suns absolute magnitude
+4.8

Suns lifetime
10 billion y




Table 2: Temperatures of Main-sequence 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





Part A Short Questions (1 mark each):

(1-8) The spectral types of 5 stars are:

Star name
Spectral type

A
F8

B
M7

C
B3

D
A0

E
O7





Answer

(1)
Which star has the highest temperature?



E

(2)
What is the approximate temperature of the hottest star?



35,000 K

(3)
Which star has the lowest temperature?



B

(4)
What is the approximate temperature of the coldest star?



2,500 K

(5)
Which star has the spectral peak nearest to 530 nm?



A

(6)
Which star has the strongest line of neutral helium?



C

(7)
If star D is a main sequence star, then its luminosity is _____ times that of the solar luminosity.



80

(8)
If the hottest star has a radius 1/10 of that of the coldest star, then its luminosity is _____ times that of the coldest star.



384




(5) Using Wiens law, the temperature of the star is 3,000,000/530 = 5,660 K. The closest temperature is that of star A, which is approximately 6,300 K.
(7) The luminosity is found from the HR diagram.
(8) Since luminosity is proportional to T4R2, the luminosity ratio is (35000/2500)4(1/10)2 = 384.


(9-15) Which of the following observations are likely to be associated with star formation?


Yes
No

(9)
Disks of gases emitting X-rays






(10)
Infrared sources within a giant molecular cloud






(11)
Hot gases surrounding a bright, blue main sequence star






(12)
Expanding planetary nebula






(13)
Jets of gas blowing away in opposite directions from a star






(14)
Emergence of dense cores of gases when surrounding dusts are driven away.






(15)
Globular clusters









(16-20) The following observations correspond to the same star during its history of stellar evolution. By locating their positions in the HR diagram, order the time sequence of their occurrence, starting from the earliest.

A: a A7 star with