Astronomy 10 Spring 2000

Worksheet #6

1. Why are binary stars valuable to astronomers? What is useful about a visual binary system (what can we learn from it)? Which parameters of the system do we have to measure for it in order to learn the masses of the stars? Why can’t we get the actual masses for stars in a spectroscopic binary system (only their ratio)?

2. Draw an HR diagram. Label the axes (both what they are, and the approximate range of values). Put the main sequence on it. Locate the Sun. Show where red giants reside. White dwarfs. Discuss the approximate mass scale along the main sequence. How can you read size off the diagram?

3. Why do stars "move around" in the HR diagram. What is happening to the star to make it "move"? Why does it go where it goes? Why do we put "move" in quotes?

4. Why is there a main sequence at all? What characteristics do the stars in it share? Are red giants older or younger than main sequence stars (this is a trick question; why)?