Physics Activities / Ver. / 0.3.4
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.1Binary 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.
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.
- 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.2The 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
1. / 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.2. / 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?
3. / 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?
4. / 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?
5. / Which spectral class is most common?
6. / Which spectral class is the least common?
7. / In general, what is the relationship between the temperature of a star and its brightness?
8. / 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?
9. / 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.
10. / 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.
11. / The book identifies three groups of variable stars. Write down their names and their characteristics.
12. / 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?
13. / 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?
14. / Why is it that black holes do not appear on the HR Diagram?
Acknowledgements
Thanks to Dr. Tim Slater[1] for using a modified version of his activity for the Hertzsprung-Russell diagram at
Appendix A - Stars which appear very bright from the Earth
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
Appendix B - Stars which are close to the Earth
Star Name / Spectral Class / Absolute Magnitude / Star Name / Spectral Class / Absolute Magnitude1. 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
Appendix C – Millimeter sheet
1
[1] Research associate professor of physics in the Department of Physics at Montana State University.