AST 301--Scalo Review for Exam 5 What is covered: All of stellar evolution, described in Chapters 19, 20, 21, and 22. Four thick chapters make for a very large amount of material, but in one way it may be easier to understand because it is unified by one theme—the story of a star’s birth (“star formation”), life (main sequence evolution), old age (red giant…asymptotic branch) and eventual death (white dwarf, supernova, perhaps gamma-ray burst, neutron star, black hole). Nearly all the material was covered in class, except for the material on black holes (22.5, 7, 8). It is up to you to read that material in the textbook (it also appears in the slides and notes). There will be relatively fewer questions on this topic, but it WILL be covered on the exam. What is NOT covered: The sections you can skip (for the exam) describe the phenomena that can occur when stars evolve in binary systems (20.6, 21.1, and binary neutron stars, 22.3). Another section that will not be on the exam is 22.6, Einstein’s Theory of Relativity. Of course you are urged to read or look through these sections for your own interest. I strongly recommend that you try the questions at the end of each chapter; I sent you a list of the questions that are most relevant by email. I’ll include them again below for completeness. I have also included selected questions from the interactive ebook selection (MC1, MC2 at the ebook web site). I do not recommend that you spend most of your study time trying to find the answers to these questions: they should be attempted after you have studied, as a self-test, although a quick look at them might be good to give you an idea of how much you understand. Fifteen minutes spent talking to someone in a study group about why you or they think a certain answer is correct could be a total waste of time. Instead, spend that fifteen minutes just trying to state what that particular question is about, and saying what you know about that topic (to yourself)—the degree of hesitation you experience in doing this will give you a good idea of why you don’t know the answer. If you are having trouble, you should go back and study the chapter again, but this time try to summarize what each paragraph or subsection was trying to get across to you in your own words. A good way to review this material is to try to “tell the story” of the evolution of stars of different masses, starting with the main sequence phase, making sure you can explain all the stages of evolution and the differences between the evolution of low-mass and high-mass stars. Each time you use some new terminology, e.g. “degenerate core,” try to explain what you mean, as if you were explaining this to someone with no background. Try some really simple-sounding questions whose answers are not simple at all. For example, “What is the difference between a brown dwarf and a white dwarf?” As you explain how their similar-sounding names have little to do with anything they have in common, ask yourself if you understand the one basic property that they do have in common, and which controls their futures; and why are they called “white” and “brown”? Another approach is contained in the notes that accompany the lecture slides. There the material is presented in a condensed way, skipping all details and irrelevant side stories, but in many cases including illustrations, not from your textbook, that I think may give you a more visual way of remembering the various phases of stellar evolution, or a visual guide for trying to tell the story yourself. Here is a condensed summary of what I consider to be the most important features of each chapter. Suggested end of chapter questions, and excluded sections, are listed for each chapter. Chapter 19. Most of this material was covered in class, and will appear on the exam. Notice that sec.19.6 (the last section, on Star Clusters) is closely related to the next chapter, especially the technique for obtaining the ages of star clusters. This is extremely important in astronomy because it is one of the only ways that we can determine the ages of stars.. Probably the most important part to feel comfortable with is sec. 19.2, because it is similar to what you’ll be reading in the next chapter, using the H-R diagram to describe the evolution of stars. However you DON’T haveto memorize the “stages” that the authors describe, not by number—i.e. I won’t ask you “In what stage does X occur?” I don’t care about the numbers, just that you understand something about the evolution, how a cloud becomes a protostar which becomes a main sequence star. Try to draw an evolutionary track for a protostar approaching the main sequence. The same statements apply to the more advanced stages of evolution described in Ch. 20 and 21. Not on exam: Sec. 19.5 Shock Waves and Star Formation End of chapter questions: Review and … (R&D): Try these as a group—they all have to do with evolutionary tracks: 1, 5, 11, 12, 15, 19. Also I suggest 6, 9, 16-18. True and False/Multiple Choice (TF/MC; I’m skipping the true and false): 11, 13, 14, 18, 19. Online eboook interactive multiple choice questions: 19: MC1: 1 (leave out “meaning” or substitute “definition”), (2*, 3, 5 on clusters), 8*, 9, 10, 12, 14 (take “fragment to mean the stage before it is opaque to its own radiation). MC2: 1 b or c are tricky: protostar is when nuclear fustion first begins, not after it is stabilized (that is the zero-age main sequence). 2 (try to answer the question, but don’t assume one of the choices given there is correct); 3 (brown dwarfs: b is misleading because “small” has nothing to do with it but “dim” is the entire answer). 6. You don’t need to know the numerical answer (it varies with mass), but that it is a small fraction of the mains sequence lifetime. 7 (think in terms of evolutionary tracks in the H-R diagram); 8 (only to see if you would know how to do this calculation; remember that the brightness per unit area varies as temp. to the fourth power, and the luminosity is this brightness times the surface area); 9* (notice the book doesn’t say how we know this—it is a theoretical result, which matches overvations well); 10 (add “where are white dwarfs?” and “where are red giants?” just to make sure you know); 11, 12, 14, 15*. Chapter 20 The evolution of low-mass stars is the primary subject here, with a short
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