Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

Reading Assignment and Study Guide intends to facilitate an easier reading of the textbook chapters. The questions are presented in sequential order as they appear in the textbook; it is therefore recommended that the reading is done along with answering the questions. Provide the answer to each question as stated in the textbook. This is not to be turned in but as a study guide for online quiz.

(Stellar Evolution from Wikipedia: http://en.wikipedia.org/wiki/Stellar_evolution)

Course Outcomes (from Montgomery College course catalog):

* Describe the origin of the stars, interstellar medium, and the life cycles of the various categories of stars

* Determind the lifetime of different stars

Learning goals:* To understand the life and death cycle of stars

Note: understanding the basics of the Hertzsprung-Russell diagram is an important learning outcome. For this chapter many overly technical and mathematical details will be de-emphasized.

Q: What else is present in regions where the youngest stars are found?

Q: What is the interstellar medium? What is its chemical composition?

Q: What is interstellar dust?

Q: What is the average distance between interstellar dust grains?

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Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

Q: How dense is the cold interstellar cloud?

Short Discussion: Provide some details about the 3 kinds of nebulae. (Nebulae in the context of this chapter will not be covered)

Q: What is another name for Emission Nebulae? What is their composition?

Q: What phenomenon causes stars to appear more red than they actually are?

Q: Why can stars be more easily observed at (near-)infrared wavelength than visible wavelength?

Q: How do the spectra of O and B stars prove the existence of the interstellar medium?

Q: What is the temperature of the interstellar medium (indicated by the narrow absorption lines of O and B stars)?

Short Discussion: What are molecular clouds, and how they can be detected?

Short Discussion: What are some sources of shock waves and how they are important to star formation? (Note: the dominant triggering mechanism in the spiral arms of the galaxy will be discussed in “Chapter 12 - The Milky Way Galaxy”)

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Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

Extra: See some animation of shock triggered star formation.http://www.youtube.com/watch?v=W13ZYepDBvohttp://www.youtube.com/watch?v=gqmSfRt610Ihttp://www.youtube.com/watch?v=LAbdyLcyk4M

Q: What can trigger repeating cycles of star formation in a giant molecular cloud? (Not sure if this matters... what is your opinion?)

Q: What is the name of a group of stars held together by gravity?

Q: What is the name for a group of stars that isn’t held together by gravity, which will all drift away from each other after some million years?

Q: What is the name of the initial formation phase of contracting clouds of dense gases in stellar formation?

Q: What is an evolutionary track of a star?

Extra: Watch the youtube video “H-R Diagram Animation” (http://www.youtube.com/watch?v=jiSN95WX1NA) and see how scientists took the image of the Omega Centauri cluster, converted what they observed into an H-R diagram, and what that showed them about stellar evolution.

Q: What is the initial state of a protostar on the H-R diagram?

Q: Why is a major reason that a protostar is difficult to observe?

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Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

Q: What happens to a protostar once nuclear reaction is triggered?

Q: How does mass affect the time of formation from protostar to main sequence star?

Q: How long did it take for the Sun to go from protostar to main sequence star?

Q: What are the two main obstacles to observing protostars?

Q: What is the name of the stage on the H-R diagram when protostars become observable at visual wavelengths?

Long Discussion Bonus: Discuss The Orion Nebula, its appearance and stars, the star formation process, and how it has changed and will continue to change.

Long Discussion Bonus: Discuss the p-p chain, the CNO chain, and how they affect stellar evolution. http://en.wikipedia.org/wiki/CNO_cycle(The successive fusion chains in a star and the radiative balance with gravity will not be emphasized as testable materials for this course. Selected testable materials will be clarified in class)

Extra: See an easy video about life of stars.http://www.youtube.com/watch?v=PM9CQDlQI0A )

Q: The stability of a star is determined by which mechanism and which two physical parameters?

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Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

[Perhaps I would eliminate following two discussion questions]Discussion Bonus: Discuss the mechanism of pressure-temperature thermostat, and also the role of gravity.

Long Discussion Bonus: discuss all important physical laws essential to the stellar structure and how it relates to pressure-temperature thermostat.

Q: Stars are power sources in balance between which two opposing factors?

Long Discussion Bonus: Discuss the four laws of stellar structure and explain what they imply for stellar structure. (+Plus: include 3 methods of energy transport and its importance in stellar evolution)

Q: What is opacity and how does it affect stellar structure?

Q: How does stellar structure theory explain the mass-luminosity relationship?

Q: How does the mass-luminosity relationship imply a lower mass limit for stars?

Q: What is the name for low-mass objects just below the main sequence’s minimal star mass?

Q: Why is the main sequence in the H-R diagram shaped like a band and not a sharp line?

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Chapter 9: The Formation and Structure of StarsAS101 Reading Assignment and Study Guide

Q: In what special region of the H-R diagram do stars begin their stable lives on the main sequence?

Q: What happens to the composition of stars when they reach the upper edge of the main sequence band?

Q: What was the Sun’s luminosity when it began its time on the main sequence 5 billion years ago (compared to its present luminosity)?

Q: How does the mass of a star correlate to its life span?

Q: If O and B stars are massive and luminous, then why are they rarely observed?

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