Astr 222 Practice Midterm

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Short Answers (25 points)

• Describe what is meant by Population I objects and Population II objects. Give examples.
• Describe the Magellenic Clouds.
• Why do we believe there is a lot of dark matter in the galaxy?
• Describe what is meant by the "luminosity function" of galaxies. In this context, what is L*? Sketch what this function looks like.
  
• Why does the X-ray variability of the galactic center place a limit on the size of the object at the center?
• Describe the Fundamental Plane for elliptical galaxies. Why is it a useful tool for studying galaxies?
• Describe how the mass-to-light ratio of the stars in a galaxy (not of the dark matter itself!) depends on the galaxy's star formation history.
• Explain why spiral arms appear strongest in blue light and weakest in red light.
• Describe how the nuclear properties of elliptical galaxies correlate with the global properties, and explain how black holes might help explain this correlation.
• Describe the "winding problem" for spiral arms. 
• Explain how a galactic bar might be destroyed.
• Describe the Kapteyn and Shapley models of the Galaxy. Explain how and why both were wrong, but one was closer to the truth.
  
• Describe the differences in the star forming histories of spiral galaxies and elliptical galaxies.
• Most spiral galaxies are not barred. Explain why this is an argument for dark matter in galaxies.
• How can you use the Tully-Fisher relationship to measure the distances to distant galaxies? What measurements would you need to make?
• Describe Cepheid stars and explain why they are important for studying galactic structure.
• Describe the Oort Limit and the physics behind it.
• Describe how the velocity dispersion of stars changes as a function of their spectral type, and why these differences occur.
• Describe the evidence for a black hole at the center of our galaxy. How massive is this black hole?
• Sketch the Hubble "tuning fork" diagram and describe how galaxies are classified this way.
• Describe the physics behind the 21cm line of neutral hydrogen and how we use it to study the interstellar medium in galaxies.
  

Numerical Problems (10 points)

• You are studying a distant star cluster, and find that the stars appear too red for their spectral type -- their colors are too red by 0.25 in B-V color. You also find that there is a Cepheid variable star in this cluster, with a period of 10 days and a mean apparent V magnitude of 7.0. How far away is the cluster?
• If your telescope can reliably measure the brightnesses of stars down to 20th magnitude, what is the farthest away you could detect a Cepheid variable? Remember that the most luminous Cepheids have period of about 100 days.
• You measure a pulsating star with a parallax of 0.005 arcseconds and an apparent magnitude of 12. What is its absolute magnitude? If it has a radial velocity of 100 km/s and a proper motion of 0.2 arcsec/yr, what is its total space motion. What part of the galaxy is this star likely a member of: the disk, the bulge, or the halo?

Essay (15 points)

• Describe the structure of the Milky Way Galaxy. Be sure to talk about the properties and relative sizes of the different components of the Galaxy. Where is the Sun's location in the Galaxy? A sketch will probably be useful here!
• Describe the Great Debate. Make sure to explain and evaluate the arguments on both sides. How did Edwin Hubble resolve this issue?
• Describe the essential differences between spiral galaxies and elliptical galaxies, and how galaxy mergers might explain how galaxies evolve from one type to the other.
• Describe in detail how a disk galaxy might evolve from a spiral to a barred spiral and back to a normal spiral. Make sure to explain the physical processes that are occuring!