Astronomy 10 Spring 2000

Homework #5

Due in one week.

Be careful of units and use appropriate precision. Be sure to explain your reasoning on each problem, so you can get partial credit for your work. Answers without explanations are not acceptable. You are encouraged to work together, but please write this up yourself.

1) Consider a twin of the Sun seen 10 light years away. What is the parallax of that star (in arsec)? What will it’s angular diameter be (in arcsec)?

2) A star is moving away from us at 100 km/s. If the "H-alpha" line appears at 656.28 nm in the laboratory, at what wavelength will it appear in the spectrum of this star?

3) An eclipsing binary system consists of 2 stars. The main sequence star has a radius 50% larger than our Sun, and a temperature of twice the Sun’s. The other is a red giant, with a temperature half that of our Sun and radius 33 times bigger than the Sun. During which eclipse will the system appear faintest: the one with the red giant in front, or with the hot main sequence star in front?

4) Explain how you could use the spectrum of a star to determine how hot it is. Consider first the overall shape of the spectrum, then secondly the absorption lines that appear in it.