Objectives: Properties of Stars

Chapter Objectives: In this chapter we learn that our Sun is a very average star that falls in the middle of the stellar range of possible luminosities, surface temperatures, and masses. We will study the laws of nuclear physics in order to understand how stars are able to release tremendous amounts of energy and yet remain so stable during their main sequence lifetimes. We will use stellar models to describe the energy transport that takes place in the hidden interiors of stars. We will show how astronomers determine the distances to stars and how they trace their motions in our sky. The H-R Diagram will be introduced as a graphical summary of some important characteristics of stars.

Over half the stars in our sky are found in pairs (binary stars) or larger groups. Analysis of these binary systems provides us with our best means of determining stellar masses and sizes. We will investigate the different types of binary stars and what can be learned from each of them about the physical properties of the stars. We will review Newton's generalizations of Kepler's laws as tools to determine stellar masses. The mass-luminosity relation that applies to most stars will be developed from these data on stellar masses. The Doppler effect will be applied to a study of binary star systems and also to the discovery of extrasolar planets. We will study the accretion of matter from one star onto another in some binary systems, and the relationship between that accretion and novae, supernovae, strong X-ray sources, and black holes.

The two types of star clusters -- the younger open clusters and the older, more crowded globular clusters -- will be introduced and the important information they reveal about stellar evolution will be discussed.

Chapter Skills: After studying this chapter you should be able to

  1. Explain the mass-energy conversion relation contained in Einstein's famous equation E=mc2.
  2. Relate "missing mass" and binding energy to the release of energy during nuclear fission and nuclear fusion.
  3. Describe the balance maintained in hydrostatic equilibrium.
  4. Discuss how energy produced in a star's core is transported to the surface.
  5. Describe the solar neutrino problem and possible solutions.
  6. Illustrate how parallax is used to measure the distances to our close neighboring stars.
  7. Define the different units used to designate the distances to stars.
  8. Describe how stars are seen to move in our sky and their actual motion through space.
  9. Define apparent magnitude and absolute magnitude and their relationship to a star's intrinsic luminosity.
  10. List and describe the main classes within the Harvard Spectral Sequence.
  11. Show how the H-R Diagram graphically demonstrates the relationship between important stellar parameters.
  12. Describe and understand the types of binary stars.
  13. Use Newton's generalization of Kepler's laws to calculate stellar masses and center of mass distances.
  14. Understand and use the mass-luminosity relation for main sequence stars.
  15. Determine the radii of stars in eclipsing binary systems
  16. Outline the steps by which astronomers determine the existence of extra-solar planets
  17. Understand the role of angular momentum in binary star system and in accretion in accreting binary systems.
  18. Understand how novae, type I supernovae, X-ray bursters, and black holes can occur in binary systems.
  19. Describe the two types of star clusters in terms of their age, evolution, stellar populations, and location in our galaxy.