1. binary stars in general:

What orbital characteristics MUST both stars in a binary share (i.e., what orbit properties must be identical for the stars)?  you should be able to think of 3 good ones.

[It might be helpful if you had a set of orbit pictures in front of you, and your book doesn't have any simple circular ones, although it does have some elliptical ones at the top right of p. 443 and the top of p. 445, which you should look at first.  So, draw your own:  assume circular orbits, because it's simple.  The center of mass will be concentric with the centers of both circles.  Choose different size circles for the two different orbits.  The drawing should now help you answer the question above)

   2.  Look at page 16 in the blue Astrophysics book.  There are two radial velocity curves (for stars labeled A and B), sort of like the radial velocity curves pictured on page 445 of Universe.  (On page 18, blue book, the radial velocity of the stars is being plotted vs. "phase" which is time, but in units of the orbit period.  Ignore the large spikes just after phase = 0 and before phase = 1 in star A's curve.)

a) why can't the plane of the stars' orbits be perpendicular to the line of sight to the earth? 

b) how fast is star B moving in its orbit?  how did you know? 

   3. It turns out that the plane of these stars' orbits are exactly edge-on; or in other words their orbit plane contains the line of sight to the earth.  Therefore each star experiences periodic eclipses by the other.

a)  which star is eclipsed (i.e., which star is behind the other) at phase = 0?  star A or star B?  The answer is contained entirely in the radial velocity graphs of RW Mon at the top of page 16!  Explain how you knew (of course!).   Remember the meaning of + and - radial velocity!

b) which star (A or B) has the larger orbit?  and how can you tell from the radial velocity curves?