Review Sheet: Test 3
Date of Exam: May 29, 2009

Version Date: May 21, 2009

Material: Class notes, Web notes, and relevant parts of Chapters 18, 19, 20, 21. The class notes are the final say on things.

Lifetime of a Main Sequence Star with mass M > 0.7 Solar Masses:
lifetime = [M/(Mass of Sun)]^-310¹⁰ years

Topics:
STELLAR PROPERTIES

What are Main Sequence Stars, giants (Red Giants), Super-Giants, Asymptotic Giant Branch (AGB) stars, white dwarfs, planetary nebulas, neutron stars?
What is the range of Main Sequence stars in terms of their mass?
What is the Mass-Luminosity relation? How can it be used to infer a scaling law for stellar lifetimes?
All stars on the Main Sequence must obey which two equilibrium laws?

Theoretical Properties of Stars:
What mechanism is used by Main Sequence stars to generate energy? By Red Giants? By AGB stars? By Horizontal Branch stars?
What is the proton-proton cycle (pp-cycle)? What is the carbon-nitrogen-oxygen cycle (CNO cycle)?
What are the energy transport mechanisms used by stars? Which ones are the most important for the Sun? Which one is the most important for Hayashi track objects? For Red Giants? For AGB stars?
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

Around what part of the Milky Way Galaxy does star formation occur? How do we deduce, based on observations, the locations of star formation in our Galaxy? What are the signatures of star formation? What are spiral arm tracers?
In what kind of Interstellar Medium (ISM) cloud does star formation occur? What are the properties of these clousd?
What is H₂? What is H II? What are H II regions? How are they formed? What are reflection nebulas? How are they formed? What is needed to form an HII region? What is needed to form a reflection nebula?
Describe the process of star formation--what triggers star formation? Why do ISM clouds collapse after thay are slightly compressed while the Sun does not collapse if it is slightly compressed? Skectch the evolutionary track of a forming star on an Hertzsprung-Russell diagram. What is the Zero Age Main Sequence (ZAMS)? What force drives star formation? How do protostars generate energy? What is the Hayashi Track? What are T Tauri stars?
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? In what parts of the electromagnetic spectrum is star formation most easily observed?
What is a protostar? At what point does a protostar become a star? What supplies the energy which allows a protostar to shine? What event signals the end of the protostar phase of evolution?
What is a Giant Molecular Cloud, a GMC? What are the properties of a GMC?
Why do upper and lower limits for the masses of Main Sequence stars arise? How does the time needed for stars to form depend on the mass of the star? Is it longer, shorter, or what for massive stars compared to low mass stars?

What is a brown dwarf? Is a brown dwarf a star?
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? What are the masses which separate planets from brown dwarfs, brown dwarfs from low mass stars, and low mass stars from high mass stars?
Draw and contrast the evolutionary tracks on an Hertzsprung-Russell diagram for the Sun and a star 25 times the mass of the Sun. Be sure to label each phase. 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 is a white dwarf? How are white dwarfs used to test our theories for the evolution of the Universe?
Discuss how the Earth changes (or may change) as the Sun evolves. What will be the fate of the Earth as the Sun evolves? Does the Earth sruvive? Does life on Earth survive?
Suppose that the Sun started from an ISM cloud which was pure helium rather than hydrogen, helium, and small amounts of other stuff. What would be different about this other Sun compared to our Sun?
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?