PHYS 413 ASTROPHYSICS

Study Guide for Exam #1

Exam #1 will be held during normal class hours on 4 March 05. You may refer to your class notes and to your homework. The test questions will be both qualitative and quantitative. The emphasis will be on the interpretation of your homework problems. The better you understand them and their consequences, the better you will do (and the quicker you will be able to complete the exam). In addition to understanding your homework, there are a few really important concepts I want you to understand:

1) VIRIAL THEORUM. What is it, what are its implications, and how is it used in astrophysics?

2) THERMAL EQUILIBRIUM. What does it mean macroscopically and microscopically? How is it established and maintained? In what astrophysical domains is it a resonable or useful approximation? Why is energy distributed equally among all possible modes, and how do the number of modes depend on temperature?

3) DISTRIBUTION (probability) FUNCTIONS. How do you calculate mean values? You should memorize (and be able to derive, at least in a qualitative way) the Maxwellian and the Planckian distributions. How/why can you parameterize a broad range of distributions in terms of a single quantity (temperature)? What microscopic processes take place in the evolution toward TE that drive all of these temperatures to the same value? Have some idea how to estimate the important collisional timescales.

4) INTERNAL PROCESSES (collisions) IN GASSES. You should be able to itemize and describe each of the common collisional and radiative (collisions with photons, though this is oversimplified, as well see in the next part of the course) energy exchanges. [e.g. Bound-Bound collisional excitation/de-excitation. Bound-free collisional excitation/de-excittation, ionization/3-body recombination.] We'll gloss over most of the scattering processes for now, but you should know that the Thompson cross-section is the relevent photon-electron scattering cross-section (and it is very important inside of stars).