The Second Exam will cover material since the last test (which ended with chapter 15, the solar interior). The current test includes all material presented in the lectures starting with the discussion of starlight. Corresponding text is : Chapters 16 (omit "rotation" on p 335), 17, 18, 19 (omit 19.5), 20, 21, 22, and 23 (black holes). We may begin studying the Galaxy (chapter 24) on wednesday, but this will NOT be on the exam.
The Exam will have a similar format to the first exam, including true/false, multiple choice and short answer questions. The review questions at the end of the chapters will help you review the material. Below are a few sample questions to give you an idea of what to expect. You might also consider reviewing Dr Hawley's ASTR 124 class web page, which includes yet more example questions, as well as more detailed notes on the individual topics.
1. T/F Pushing a star to 5 times its current distance, it will appear 5 times fainter.
2. T/F A 15th magnitude galaxy appears 1 million times fainter than the bright star Vega, which has magnitude 0.
3. T/F A star with color index B$-$V$ = +0.2$ is hotter than a star with B$-$V$ = +0.8$.
4. T/F A K2 star is slightly hotter than a G2 star.
5. What spectral type of star has strong molecular absorption lines ?
6. T/F The absorption lines of red giants are narrower than the absorption lines of red main sequence stars.
7. Sketch an HR diagram. Label the axes. Indicate where the various types of stars are found.
8. What is the approximate main sequence luminosity of a 2 solar mass star, in units of the suns luminosity ?
9. Which type of binary system provides the most information about its component stars' masses and sizes?
10. T/F A star with a parallax of 0.2 arcsec is 2 parsecs away.
11. How do Cepheid variable stars allow us to determine their distance ?
12. Describe, briefly, the four major gas phases of the interstellar medium. How do we detect each of these ?
13. Which of the following is NOT a property of interstellar dust?
14. Which of the following is FALSE
15. T/F HII region emission nebulae are generally found in association with hot O and B stars.
16. T/F As a star gradually uses up the hydrogen in its core, it begins to cool off and the star moves down the main sequence.
17. As the supply of hydrogen is exhausted in the core, a star's
18. Consider the evolution of the Sun, from birth to death. For each stage, describe how energy is generated, and where on the HR diagram the sun located.
19. It is likely that the sun will become a white dwarf without any mass loss.
20. White dwarf stars
21.Cluster 1 has a main-sequence turnoff at spectral type A2; Cluster 2 has a turnoff at spectral type F2. Which of the following must be true?
22. There are several important differences between the interiors of high mass stars (eg 10 solar masses) and low mass stars (eg 1 solar mass). Which of the following is NOT true for high mass stars compared to low mass stars:
23. T/F Neither fission nor fusion of iron nuclei yields any energy
24. T/F Supernova core collapse takes about an hour
25. T/F In a type II supernova (core collapse) most of the energy emerges as kinetic energy of the expanding ejecta.
26. T/F A neutron star of mass 2.2 solar masses is larger than neutron star of mass 1.8 solar masses
27. T/F The Crab pulsar spins 30 times per second and weighs 10 solar masses.
28. Which of the following is NOT a property of ALL pulsars?
29. Pulsars slow their pulse rate because
30. Novae are caused by nuclear explosions:
31. T/F A Million solar mass black hole has a Schwarzschild radius 1 million times larger than that of a one solar mass black hole.
32. T/F Einstein showed that measurements of space and time were the same for all observers, independent of their state of motion.
33. Gas about to cross through the event horizon of black hole emits radiation in the form of an emission line. This radiation is observed to be:
34. Which of the following would be sensible strategies for finding a black hole :
Here is a list of the major themes we have discussed in class, presented partly in question form. This should give you some idea of the range and scope of the topics. It is compelmentary to the concept list you got at the beginning of the class, and should help you review the material.
A. What is the difference between a star's apparent brightness and its luminosity, and how are these two quantities related (know a formula which gives one in terms of the other). What is the inverse square law of brightness ?
B. Know the magnitude scale, its historical roots, and its more modern form. Are stars with small magnitudes brighter or fainter than those with large magnitudes ? Know that a difference of 5 magnitudes corresponds to a factor of 100 in brightness.
C. Understand how colors of stars can be determined from their magnitudes through U, B, and V filters. Remember that a large B-V color index is a red star. Star colors, of course, correspond to surface temperature (blue=hot, red=cool).
D. Know that a star's temperature also determines the kind of absorption lines seen in its spectrum. Know the temperature sequence O,B,A,F,G,K,M and which absorption lines correspond (approximately) to which spectral type. What is Luminosity Class; what are classes I, III, V called; and what is different about the absorption lines of each class. How do we know the sizes of stars. Know that the Sun has spectral type G2 and luminosity class V.
E. Know the Herzsprung Russell diagram, and what types of stars appear where on the diagram - main sequence, giants, white dwarfs. Know that for main sequence stars, the mass of the star determines where it is on the main sequence - (mass increases from lower right to top left). Know the mass luminosity relation (L proportional to M3.5); and understand why this means luminous stars have shorter lives.
F. How are star masses measured. Know the different classes of binary star. Is binarity rare or common ?
G. How do we measure distances to stars; how is a "parsec" defined; know the relation between parallax angle (in arcsec) and distance to a star (in parsecs).
H. What is the instability strip, and why do some stars vary regularly in their brightness. Know the term Cepheid Variable stars, and why such stars are useful for measuring distances.
I. Know the basic phases of the interstellar medium : cold, warm, hot, very hot. Remember each is in approximate pressure balance. How is each detected. Know about the HI 21 cm emission line of hydrogen, as well as molecular radio emission. Know about interstellar dust and how it affects the passage of light through the galaxy. Which is absorbed and scattered by dust more : blue or red light ? Know that stars behind dust appear dimmer and redder. Know that dust can scatter light from nearby stars, creating reflection nebulae.
J. Know the basic stages of star formation --- starting from the interstellar medium, and ending on the main sequence. Know when gravity powers the star and when nuclear reactions do. What triggers star formation ? How is star formation best observed ? How do planets figure into the star formation process ? What are brown dwarfs ? What are HII regions, and why is the gas ionized. Do stars form in isolation or in groups. Know that groups of stars tend to disperse as time goes by ?
K. Know how low mass stars like the sun evolve with time --- what changes occur inside the star, how do these correspond to the location of the star on the HR diagram, and how long (approximately) do these stages last ? Know about core and shell burning; hydrogen and helium burning. Know the terms main sequence, red giant, horizontal branch, asymptotic giant branch, and where they are on the HR diagram.
L. Understand how a cluster of stars appears on the HR diagram -- they form an 'isochrone' since they all have the same age. Know how the age of the cluster can be measured from the "main sequence turn off point". Know the two types of clusters : open clusters, young, in the disk, metal rich; and globular clusters, old, in the halo, metal poor.
M. How do low mass stars die. What is a planetary nebula. Know the basic properties of white dwarf stars, and that they are supported by electron degeneracy pressure. Know (roughly) what degeneracy pressure is, and that is it independent of temperature. What is the Chandrasekar mass limit ?
N. How do high mass stars evolve, and how does their evolution differ from low mass stars ? Know, roughly, the sequence of nuclear fuels, with its endpoint at Iron. What is meant by "Onion Shell Structure". Understand (roughly) how core collapse happens, and how the star explodes in a Supernova (Type II) explosion. How is the energy released shared amongst neutrinos, kinetic energy and light ? Know that Gravity is the ultimate origin of the energy. How did SN 1987A help confirm the basic understanding of this type of supernova. What does the supernova light curve look like, and what determines the gradual (exponential) fading of the supernova remnant.
O. Understand the constant cycle of matter from the interstellar medium into stars and then back again. Understand also that stellar evolution (in particular supernova explosions) gradually add new chemical elements to the interstellar medium. Realize that almost all the elements in the earth (and in you) were created in earlier generations of stars that died several billion of years ago. Know, roughly, how the trans-iron elements are made by neutron addition.
P. What stellar corpses remain at the end of the life of a High Mass star ? Know the basic properties of Neutron stars --- size, mass range, density, surface gravity. What kind of pressure supports these types of stars. Are higher mass neutron stars larger or smaller than lower mass neutron stars. Know that there is an upper mass limit of about 3 solar masses for neutron stars. What happens above this limit ?
Q. Know, roughly, the history of discovering pulsars. What are pulsars ? Why do neutron stars spin fast when they are created ? Why do they have such high magnetic fields ? Know, roughly, the reason we see regular pulses of radio emission. Know what Synchrotron emission is. What is the simple evidence that pulsars gradually slow down.
R. Know how mass transfer onto a white dwarf in a binary star leads to a Nova (surface Hydrogen detonation). Know the related phenomena of X-ray bursters when the mass transfer is onto a neutron star (surface helium detonation).
S. Know that further mass transfer onto a white dwarf in a binary can lead to the nuclear carbon detonation of the entire star, causing a Supernova (Type I) explosion. Know that in these supernovae, the ultimate energy source is nuclear.
T. Understand the basic term "Black Hole" -- why is it black and why is it a hole ? How is the Schwarzchild radius of a black hole defined. Know that it is proportional to the mass of the black hole, with a value of 3km for each solar mass. Understand that above 3 solar masses, no pressure exists to support the mass.
U. Understand, roughly, the difference between Newton's and Einstein's description of Space, Time, and Gravity. Understand, roughly, what curved space-time is, and how motion across it can seem like a force is acting. Know some of the tests of General Relativity : Precession of the Perihelion of Mercury; the effect of the Sun's gravity on the positions of stars; the slowing of time for clocks closer to the earth than further; the gravitational redshift.
V. Know the properties of black holes : how time slows down near them, how light is redshifted, and how strong tides will shred objects near them. Know about rotating black holes, and how the surrounding region is somewhat different from a non-rotating black hole. Know about Hawking radiation and the gradual evaporation of black holes.
W. How are black holes detected by astronomers ? Know about the two basic masses of naturally occurring black holes : stellar remnants (few solar masses) and galactic nuclei (million to billion solar masses). Understand how a variability time tells us something about the maximum size an object can be.
Do the 34 questions, write down your choice of answers, then check yourself with these Answers Think about the ones you missed. If you missed several, redouble your study efforts ! Also, dont forget the TA office hours in room 267 of 10am - 1pm (Mon, Tues, Thurs) and 3:30pm - 6:30pm (Wed, Fri). And my own office hours 2pm to 3pm (Tues, Thurs).