Review Sheet: Test 2
Date: Tuesday, 14 August 2007

Material: Class notes and relevant parts of the Web notes and Chapters 16, 17, 18, 19, 20, 21 (the relevant parts are determined by the lecture content). The class notes are the final say on things.

Formulas:

• Blackbody Laws:
  • Wien's Law -- The wavelength at which a blackbody appears the brightest is inversely proportional to the temperature of the blackbody, i.e.,

    W = 3x10⁷/T(K) Angstroms, or T = 3x10⁷/W K

    where 1 Angstrom = 10^-8cm

  • Stefan-Boltzmann Law -- The power radiated per unit area from a blackbody is proportional to fourth power of the temperature, i.e.,

    Flux = constant x T⁴

• Flux from a star at distance, D:
  Flux ~ Power / D²

• Luminosity of a star of temperature T and radius R:
  L = 12.6 R² T⁴
  • Schwarzschild Radius
    _Sch = 3 [M/M(Sun)] km

  Topics:

  STELLAR PROPERTIES (as a reminder)

  • What is the Herzsprung-Russell Diagram? (HR) Draw an HR diagram and carefully label the various portions of the diagram. What information can we deduce about how stars evolve, the most common types of stars, ... from the HR diagram (directly and when coupled with other information, such as the blackbody laws)? What are Main Sequence Stars, giants (Red Giants), Super-Giants, Asymptotic Giant Branch (AGB) stars, white dwarfs, planetary nebulas, neutron stars?
  • What is the Russell-Vogt theorem? State the Russell-Vogt theorem. What are the most important stellar parameters according to the Russell-Vogt Theorem??

  The properties of the Sun:
  • What is the Quiet Sun? What is the active Sun?
    • Describe the appearance of the Quiet Sun and list its properties. What are the properties of the photosphere, the chromosphere, the corona?
    • What are sunspots? What are the umbra and the penumbra of a sunspot? How many times brighter is the surrounding Solar photosphere than the umbra of a sunspot?
    • What are quiescent and eruptive prominences? What are filaments? What are flares? What are CMEs? What property of the Sun seems to unite all the phenomena of the Solar Activity Cycle?
    • What is the period of the solar activity cycle? The period for the variation of the number of sunspots visible on the surface of the Sun? What is the Maunder minimum? What is the significance of the Little Ice Age which struck Europe in the mid 1600s (in terms of Solar variability)? Roughly, how large is the variation of the Solar power (Solar constant) over a Sunspot cycle. Are there noticeable effects of this variation on the climate of the Earth?
    Theoretical Properties of the Sun and Stars:
    • What are the different ways discussed in class that stars can generate energy? What is the most efficient way to generate energy of those mentioned in class? What physical concept underlies the famous Einstein result that E = mc²?
    • Nuclear Energy Generation--the conversion of 4 hydrogen nuclei into a helium nucleus + energy + other particles. Why is nuclear fusion so difficult (that is, what is the major impediment to fusion)?
    • What is the proton-proton cycle (pp-cycle)? What is the carbon-nitrogen-oxygen cycle (CNO cycle)?
    • How can fission and fussion both generate energy? Since both fusion and fission can generate energy, are nuclear reactions an unlimited source of energy?
    • What are the energy transport mechanisms used by stars? Which ones are the most important for the Sun?
    • What is Tunneling? Why is it important for stars? What is the Heisenberg Uncertainty Principle? Compare and contrast matter and anti-matter. What is annihilation? What is the Heisenberg Uncertainty Problem?
    • Main Seqeunce stars are in equilibrium; both mechanical equilibrium (hydrostatic equilibrium -- stars are not changing in size very quickly) and thermal equilibrium (the temperature structures of stars are not changing very quickly -- the energy losses due to radiation and particles from stars are roughly balanced by the energy production due to nuclear fusion reactions).
      • Hydrostatic Equilibrium -- We need to address what holds stars together (gravity), and to address what keeps stars from collapsing into dense balls (gas pressure).
      • Thermal Equilibrium --We need to address the energy source for stars and how stars lose energy.

  STAR FORMATION

  • Is star formation an ongoing process? How do we deduce whether or not star formation is an ongoing process? Will it continue forever?
  • In which region of our Galaxy does star formation occur? In what kind of Interstellar Medium (ISM) cloud does star formation occur? What objects are markers for the star formation process?
  • Describe the process of star formation--what triggers star formation? What force drives the process of star formation?
  • What are the different components of the ISM? Which parts are important for star formation? What is dust? What are some reasons dust is important to astronomers? What blocks out the visual light from distant stars? Gas or dust? Explain why your answer is correct? Why is the setting Sun red? Why is the sky blue?
  • What is a protostar? At what point does a protostar become a star?
  • What is a Giant Molecular Cloud, a GMC?
  • How do the upper and lower limits for the masses of Main Sequence stars arise?
    • What is a brown dwarf?
    • What is degeneracy pressure? How does the pressure change as a degenerate gas is heated? as it is cooled?

  STELLAR EVOLUTION

  • Explain why stars have to evolve. Do stars evolve while they are on the Main Sequence? What formula relates the Main Sequence lifetime of a star to its mass? How long will a 50 solar mass main sequence star live? How long will a 0.1 solar mass main sequence star live?
  • What is nucleosynthesis? What is the most massive element made in normal stellar evolution? In what nuclear burning stage is the Sun? The Sun's core will eventually become composed of what 2 elements?
  • What are the major burning cycles for normal stars? Why doesn't the Sun form an iron core?
  • Massive stars vs. Low mass stars (What criterion is used to define low mass vs high mass stars?). Are the stellar remnants left by low mass and high mass stars different? How do high mass and low mass stars end their normal phases of stellar evolution?
  • Draw and contrast the evolutionary tracks on an Hertzsprung-Russell diagram for the Sun and a star 25 times the mass of the Sun. Pay attention to the nuclear burning and the various stages each star passes through. For massive stars, describe the different nuclear burning phases and how long each lasts. After which burning stage does neutrino emission dominate the production of radiation in a star?
  • After a star enters the carbon burning stage, its outward appearance does not change very much even though its source of nuclear energy changes. Why is this so? How could we tell what stage of nuclear burning it is going through?
  • Explain in words why and how a star like the Sun evolves. Be careful to explain clearly the difference between the evolution of the core and the outer layers (the mantle).
  • What forms of energy transport are important for stars?
  • What is meant by shell burning?
  • What triggers the rise of a star along the Red Giant Branch, the Asymptotic Giant Branch?

  White Dwarfs:

  • How are most white dwarfs formed?
  • What are the properties of a typical white dwarf? (What is the typical mass of a white dwarf, the typical radius, density?)
  • Describe the white dwarf mass radius relation. What is the Chandrasekhar mass limit? Why does the Chandrasekhar mass limit arise?
  • How can white dwarfs be used to place a lower limit on the age of our galaxy?

  Stellar Clusters:

  • What is the observational study of stellar evolution difficult?
  • How are stellar clusters used to test our understanding of stellar evolution?
  • What are the properties of a cluster of stars that makes the cluster a valuable test of our understanding of stellar evolution?
  • Sketch the Hertzsprung-Russell diagrams for clusters of various ages?
  • Will a cluster show a fully occupied Main Sequence (stars all the way from O stars to M stars)? Why not (if not)?
  • Explain how stellar clusters can be used to place lower limits on the age of the galaxy. What is the largest age found for a stellar cluster? Does this age have implications for our understanding of cosmology (the evolution of the Universe)?
  • What are globular clusters? What are galactic clusters?

  SUPERNOVAS:

  • What are Type I Supernovas? What are Type II Supernovas? What are SN remants? What is the Crab Pulsar? What are criterion is used to differentiate between Type I and Type II Supernovas?
  • How is the energy generated in a Type II SN divided among neutrinos, the explosion, the radiation.
  • What role do SN play in nucleosynthesis? What is the r-process? What is the s-process? Why are SN able to make elements more massive than Fe?
  • What is meant by Historical Supernova? What are the historical SN? What is the last historical SN? What is the rough rate for SN in a galaxy like the Milky Way?
  • What type of stars produce Type I SN? What type of stars produce Type II SN? Describe both Type I and Type II Supernovas.
  • What is the observational evidence that suggests that our understanding of Type II SN is reasonably good.
  • What energy source powers the light produced by a Type I SN after a few months. Does this energy source play a role in the evolution fo Type II SN light curves?