Review Sheet: Test 4
Date of Exam: September 3, 2009

Version Date: September 2, 2009

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

Topics:
Star Formation, Stellar Properties, and Stellar Evolution
Stellar Properties

What are Main Sequence Stars, Subgiants, giants (Red Giants), horizontal branch stars, Super-Giants, Asymptotic Giant Branch (AGB) stars, white dwarfs, planetary nebulas, black dwarfs, brown dwarfs?
What is the range of Main Sequence stars in terms of their mass? Do we have explanations for the observed mass range? What are the explanations for why there is an upper mass limit and a lower mass limit for Main Sequence stars?
All stars on the Main Sequence must obey which two equilibrium laws?
What mechanism is used by Main Sequence stars to generate energy? By Red Giants? By AGB stars? By Horizontal Branch stars? By white dwarfs? By protostars? By T Tauri stars?
What is the proton-proton cycle (pp-cycle)? What is the carbon-nitrogen-oxygen cycle (CNO cycle)? What is the Triple Alpha process?
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?

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?
What is the Interstellar Medium (ISM)? Of what kinds of materials is the ISM composed? What is dust? What are the properties of the dust? What are some important consequences of the dust in the ISM?
In what kind of Interstellar Medium (ISM) cloud does star formation occur? What are the properties of these clouds?
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? Are the following non-sequitors or are they related to the current discussion? 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? If so, why? 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?
What is the Helium Flash? Why does it occur? What is rate energy is produced in the Helium Flash? How long does it last? Why are the observable effects of the Helium Flash small?
Offer an explanation for the formation of planetary nebulas. What is thermal pulsing? What kinds of stars produce planetary nebulas? What important astrophysical role do planetary nebulas play?
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 the evolutionary track on an Hertzsprung-Russell diagram for 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?
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 the effects on the Earth produced by the evolution of the Sun. 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 is shell burning?
What triggers the rise of a star along the Red Giant Branch, the Asymptotic Giant Branch?