This document discusses properties of stars and stellar evolution. It asks the reader to: 1) Sketch HR diagrams of young and old star clusters and explain equations relating mass, luminosity, and lifetime on the main sequence. A 20 solar mass star is compared to the Sun. 2) Explain why hydrogen Balmer lines are strongest at 10,000K and weaker at higher temperatures, and if other atomic transitions can be used similarly. 3) Identify what is causing the radial velocity wobble of 47 Ursae Majoris from a graph, cite the relevant Newtonian law, and calculate the orbital period.

1. 1. (a) Sketch the HR diagram of (i) a young cluster of stars (ii) a very old cluster of stars. (b)
Write and explain the equation for mass vs. luminosity on the Main Sequence. (c) Write and
explain the equation for lifetime vs. mass on the Main sequence. (d) A 20 solar mass star is on
the Main Sequence. Compare its luminosity and lifetime on the Main Sequence to those of our
Sun. 2. Hydrogen Balmer lines in stars are strongest at temperatures of 10000K. Why do they get
stronger as the temperature approaches 10000K and weaker at high er surface temperatures?
Explain in detail. Can other transitions in other atoms be used as a thermometer? 3. The
following radial velocity graph depicts the wobble back and forth of the star 47 Ursae Majoris.
(a) What is causing the star to wobble? (b) Which of Newton's laws makes it possible for us to
come to this conclusion? (c) Calculate the orbital period from this graph. 47 Ursae Majoris
(HR4277)