1) Besides temperature and density, one other property of a star that is related to its line width is its rotation speed (and orientation with respect to Earth).

a) (9 pts) Explain (a diagram may help but is not required) why the rotation of a star seen from the star's equatorial plane will result in line broadening.

b) (5 pts) Will a rotating star seen pole-on also show the effects of rotational line broadening? Explain your answer in a single sentence.

2) Below is an energy level diagram for an atom of some unknown element, X:

State below (yes or no) which of these energies can be absorbed by this atom of element X with the electron in level 2. No explanations needed.

		E = 3  ________________		E = 12  ________________

		E = 5  ________________		E = 14  ________________

		E = 9  ________________		E = 20  ________________

Also, state which of the absorbed photons has the shortest wavelength:

3) Temperatures in the corona are actually higher in some places than temperatures in the Sun's core. However, we know that fusion doesn't occur in the corona because the density is not sufficiently high.

a) (7 pts) Explain why high density is required in order for fusion to take place.

b) (7 pts) Explain why the temperature in the corona is so high.

4) In the constellation Orion, the star Betelgeuse has a surface temperature (3,000 K) about half the surface temperature of our Sun (6,000 K).

a) (2 pts) We expect the continuous radiation spectrum of Betelgeuse to peak at (longer, shorter, the same) wavelength relative to our Sun.

b) (12 pts) Justify your answer to part (a).

5) Explain the "solar neutrino problem". Despite this conflict with the predictions of scientific theory, Astronomers still believe that nuclear fusion is the source of the Sun's energy. Explain why.

6) To find the mass of some stars, Astronomers exploit the properties of binary star systems. If the system is edge-on, it is relatively easy to measure the orbital velocity and the period from the Doppler shift of the companion star.

a) (7 pts) Explain how these two pieces of information are used to determine the mass of the central star.

b) (7 pts) Suppose the system we're observing is not really edge-on. We assume it is edge-on, but it is really tilted slightly so that not all of the motion is radial. Our estimated central star mass will be (larger than, smaller than, the same as) the true central star mass. Explain your answer.

7) Star A has a surface temperature of 12,000 K. Star B has a surface temperature of 6,000 K. The radius of star A is one-half the radius of star B.

a) (7 pts) State how the absolute luminosity of star A compares to the absolute luminosity of Star B. Show your work.

b) (7 pts) Suppose star A is twice as far from the Earth as star B. State how the apparent luminosity of star A compares to that of star B numerically (e.g. ³Star A¹s apparent luminosity is 6 times larger than star B². Show your work.

8) The closest star to our own Sun, Proxima Centauri has a surface temperature of about 3,000 K, much cooler than our Sun's temperature of 6,000 K. Proxima Centauri has a composition nearly identical to that of our Sun, but if you compare the strength of the Magnesium lines between Proxima Centauri and our Sun, you would find that the Magnesium absorption lines in the Sun's spectrum are much weaker. Explain the most likely reason these two spectra are different.