Unit 4 HW 2(1) (1)

Unit 4 HW 2 PART I: Remembering 47 Tuc…a retrospective FILL IN THE BLANKS WITH THE MOST APPROPRIATE TERMS. SOME WORDS MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. IN SOME CASES, MORE THAN ONE TERM MIGHT BE APPROPRIATE. PLEASE TURN IN AT THE END OF CLASS. emission absorption parallax luminosity smaller larger continuous temperature spectroscopic parallax age mass main sequence dimmer brighter distance absolute magnitude HR Diagram hotter cooler spectral type luminosity class red giant white dwarf apparent magnitude redshifted Wow, 47 Tuc. When I first saw you, I was most impressed with the fact that your stars were different colors. Now I know that the colors give me a clue about the temperature of your stars. Of course, you didn’t stop there. I also found that if I split up the rainbow enough, I would see that your stars showed absorption spectra, just like the Sun and most other stars in the sky. If I analyzed the dark lines in your stars’ spectra more thoroughly and saw how broad/fuzzy or narrow/in-focus they appeared, I could even tell the luminosity classes of your stars. Only then could I figure out your distance , because our technology just isn’t good enough for us to triangulate on you and find a simple parallax . You sure kept me guessing on that one, 47 TUC, but I finally figured you out. Then I was amazed to find that the distance to all of your stars is essentially the same, which means that your orange stars must be brighter and hotter than your white stars. Then we took a look at how your stars’ temperatures and luminosities compared. Wow, your color-magnitude diagram definitely didn’t look much like the one for the Pleiades at all. In fact, that strip of hydrogen-fusing stars - your main sequence , that is - didn’t extend beyond spectral type G0. By understanding binary stars, we found out that the mass of your largest main sequence star was a bit more than the Sun, and knowing this “turnoff” helped me figure out your age . Alas, you were too young to die… Anyway, thanks for everything, 47 TUC. I’ll miss you (at least, after the 4 th exam), but I wanted to say that I now understand stars so much better because of you. PART II: Questions that aren’t quite so depressing….

1. What evolutionary events occur in a sun-like star from the original giant cloud to the end? How long does each phase take? How do astronomers observe these events? a. Red giant, protostar, molecular gas, and white dwarf. The aid of emission lines. 2. What is a planetary nebula? What sort of spectrum do astronomers see from the outer layers of a planetary nebula? What is at the heart of a PN? a. The white-hot core of a low-mass star is within the shell of a planetary nebula. 3. What is a white dwarf? Describe a typical white dwarf (composition, temperature, radius, mass, location on the HR diagram). a. Small dense star that's the size of a planet, bottom left side of the HR Diagram, stars with the smallest radius, mass, and hottest temperature. 4. What holds up a normal, main sequence star against gravity? What holds up a white dwarf against gravity? a. Electron degeneracy pressure 5. What makes a white dwarf a useful tool in determining the age of a galaxy or star cluster? a. How long they have been cooling determine how old a galaxy is. 6. What evolutionary phases are common to both low-mass and high-mass stars? a. Main sequence, hydrogen fusion, helium fusion, and carbon fusion. 7. What is significant about the fact that iron is an ‘energy dead end?’ What happens to the core as soon as it becomes iron? What effect does this have on the rest of the star? a. Core will have 0 charges left, becomes small and neutral, causes star to blow up. 8. How are the elements beyond iron on the periodic chart created? What is the r-process? Why can’t the r-process happen without a supernova? a. Explosive stars collide with one another, and the greatest supernova's energy is needed for fast neutron capture nucleosynthesis. 9. What holds up a neutron star against the inward crush of gravity? a. neutron degeneracy pressure 10. What is a pulsar? Why do they “pulse?” How do astronomers detect neutron stars? What is a typical radius and mass of a neutron star? a. A neutron star whose spin axis and magnetic axis are not aligned. 11. What is the definition of a black hole? What would happen to the orbit of Earth if the Sun were to instantly become a black hole? a. Area of space where light is drawn by gravity and cannot escape