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Physics Activities
Last updated 11.01.02
Activities for Option F.2
Activitities are unassessed short experiments with some problems (pre questions, post questions, and syllabus
questions) assigned. These problems will be a starting point for class discussion on the material after the
activities. Due to time restrictions some of the problems will be given as homework.
Text book reference:
Section 14.2, “Types of Stellar Objects” in Chapter 14 - Astrophysics - pp. 559-562 of
Gregg Kerr, Nancy Kerr and Paul Ruth, Physics,
IBID Press 1999, ISBN 0-958-56867-7
A.1 Binary Stars
Aim
One aim is to know the difference between visual binaries, eclipsing binaries and
spectroscopic binaries. Another one is to understand their different properties by
kinesthesic simulation.
Syllabus reference
F.2.4
Group size
Three to four
Equipment
Two stars (i. e. students)
Procedure:
1.
Most of the stars in the universe are actually a binary system, i. e. two stars that
revolve around their common center of mass. The set of all binary systems are often
divided into visual binaries, eclipsing binaries and spectroscopic binaries. Use the
book to find the difference between these three cases.
2.
Assume that the star 1 and star 2 in the diagram below are visual binaries or eclipsing
binaries and that they have equal intensity. Your task is now to find the maximum and
minimum intensity as seen from the earth. Let two members of the group simulate
(slowly) the rotation of the two stars about a common point and let the other members
(the Earth) determine if the intensity will increase or decrease. Make a sketch that
shows intensity vs time where the unit along the time axis is a quarter of a period.
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3.
Make a similar sketch if star 1 is much brighter than star 2. Starting with a simulation
will probably make the result much clearer.
4.
Assume now that the stars are spectroscopic binaries. It is known that if a star is
radially approaching the earth the light spectrum will be blueshifted (all wavelengths
become smaller) and if a star is moving radially away from the earth, the light
spectrum will be redshifted (all wavelengths become larger). Use the four positions in
the figure under part 2 to predict which star(s) that are blue/redshifted if a shift
appears. A simulation might make the various cases more clear.
5.
Several of the star names in the table of Appendix B appear twice followed by an A or
a B. These are mostly double stars - two stars which are revolving around each other
together in space. They seem to frequently have similar spectral types. Can you guess
why they have similar spectral types?
A.2 The Hertzsprung-Russell Diagram
Aim
The aim of this activity is to plot near stars and bright stars on a color magnitude
diagram. White stars, red giants, the main sequence and possible variable stars are also
identified.
Syllabus reference
F.2.1 – F.2.3
Group size
Two
Equipment needed
Pencil
Paper
Procedure
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1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Using the list of bright stars in Appendix A and the list of near stars in appendix B, plot
their absolute magnitude vs. spectral class on the attached graph in appendix C. Use
different colors for the near stars and for the bright stars.
What general trends or concentrations do you see in the data? Are there generalizations
you can make about bright stars? Any generalizations about near stars?
This diagram was first published by Henry Norris Russell and Ejnar Hertzsprung in the
early 1900's. It is sometimes called a color - magnitude diagram. Why is this ( or why is
this not) an appropriate name for a plot of magnitude versus spectral class?
Our star, the Sun, is a G2 spectral class star with an absolute magnitude of 4.8 . How
does it compare to the locations of the near stars on the diagram? How does it compare
to the locations of the bright stars on the diagram?
Which spectral class is most common?
Which spectral class is the least common?
In general, what is the relationship between the temperature of a star and its brightness?
Most of the stars seem to be along a line from the upper left corner to the lower right
corner of the HR Diagram. Stars which fall into this category of stars are called main
sequence stars . Does our Sun fit into this category?
White dwarfs are hot dim stars while red giants are bright cool stars. Where (i.e. in
which regions) should these two types of stars be in the diagram? Identify at least one
red giant and one white dwarf.have low surface temperature and large negative absolute
magnitude.
A bit above the middle of the main sequence are the variable stars, called so since they
have a time variation of their magnitude. Identify from your diagram at least one
candidate for a variable star.
The book identifies three groups of variable stars. Write down their names and their
characteristics.
Stars which are "on the main sequence" are generally very stable stars which are
combining their hydrogen atoms into larger helium atoms (this reaction is called fusion
and gives off energy). Where in the star do you think that this fusion reaction is most
likely occurring? Why?
Main sequence stars which are very bright are fusing hydrogen atoms into helium
atoms at an enormous rate. Do you think that these bright stars will burn forever? How
long do you think these stars will shine compared to the dimmer main sequence stars?
Why is it that black holes do not appear on the HR Diagram?
Acknowledgements
Thanks to Dr. Tim Slater1 for using a modified version of his activity for the HertzsprungRussell diagram at http://solar.physics.montana.edu/tslater/plunger/hr_diag.htm.
1
Research associate professor of physics in the Department of Physics at Montana State University.
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Appendix A - Stars which appear very bright from the Earth
Star Name
Spectral Absolute
Star Name
Class Magnitude
Spectral
Class
Absolute
Magnitude
1. Sirius A
A1
+1.4
19. Aldebaran A
K5
-0.2
2. Sirius B
B8
+11.5
20. Aldebaran B
M2
+12
3. Canopus
F0
-3.1
21. Crucis A
B1
-4.0
4. Centaurus A
G2
+4.4
22. Crucis B
B3
-3.5
5. Centaurus B
K5
+5.8
23. Antares A
M1
-4.5
6. Arcturus
K2
-0.3
24. Antares B
B4
-0.3
7. Vega
A0
+0.5
25. Spica
B1
-3.6
8. Capella A
G0
-0.7
26. Pollux
K0
+.08
9. Capella B
M0
+9.5
27. Fomalhaut A
A3
+2.0
10. Capella C
M5
+13.0
28. Fomalhaut B
K4
+7.3
11. Rigel A
B8
-6.8
29. Deneb
A2
-6.9
12. Rigel B
B9
-0.4
30. Beta Crucis
B0
-4.6
13. Procyon A
F5
+2.7
31. Regulus
B7
-0.7
14. Procyon B
F0
+13.0
32. Adhara
B2
-5.0
15. Achernar
B5
-1.0
33. Castor A
A1
+2.1
16. Beta Centari
B1
-4.1
34. Castor B
A5
+2.9
17. Betelgeuse
M2
-5.5
35. Castor C
K6
+8.8
18. Altair
A7
+2.2
36. Shaula
B1
-3.3
-
-
37. Bellatrix
B2
-4.2
-
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Appendix B - Stars which are close to the Earth
Star Name
Spectral Absolute
Star Name
Class Magnitude
Spectral Absolute
Class Magnitude
1. Sun
G2
+4.8
16. Procyon A
F5
+2.7
2. Centari A
G2
+4.4
17. Procyon B
F0
+13.0
3. Centari B
K5
+5.8
18. Struve 2398
M4
+11.1
4. Centari C
M5
+15.0
19. Struve 23948
M5
+11.9
5. Lalande 21185
M2
+10.5
20. Groom 34 A
M1
+10.5
6. Sirius A
A1
+1.4
21. Groom 34 B
M6
+13.2
7. Sirius B
B8
+11.5
22. Lacaille 9352
M2
+9.6
8. Ross 154
M4
+13.3
23. Tau Ceti
G8
+5.7
9. Ross 248
M5
+14.7
24. BD +5 1668
M4
+11.9
10 Epsilon
Eridani
K2
+6.1
25. Lacaille 8760
M0
+8.7
11. Luyten
M5
+14.7
26. Kapteyn's Star
M0
+8.7
12. Ross 128
M5
+13.8
27. Krueger 60 A
M3
+11.8
13. 61 Cygnus A
K5
+7.5
28. Krueger 60 B
M4
+13.4
15 61 Cygnus B
K7
+8.3
29. Ross 614
M5
+13.1
15. Epsilon Indi
K5
+7.0
30. BD -12 4523
M4
+12.0
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Appendix C – Millimeter sheet
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