Review Questions

1. In your own words, describe what "detailed balancing" is and its importance in understanding microphysics in astrophysical gases.

2. Consider Figure 34.1. In your worn words, describe the process being illustrated in each of the figure panels.  That is, what is radiative excitation, etc.? For each panel, describe what is happening to the photon, what is happening to the electron, and how the state of the atom/ion changed. For each, also describe how the energy content is changed (i.e., increased or decreased) in the (i) radiation field, in the (ii) particle field, and (iii) internally in the atom/ion.

3. What is the difference between a cross section and a rate coefficient? Why does photoionization invoke cross sections, whereas collisional ionization and recombination invoke rate coefficients?

4. Describe the following processes: (i) photoionization, (ii) Auger ionization, (iii) direct collisional ionization, (iv) excitation auto-ionization, (v) radiative recombination, (vi) dielectronic recombination, and (vii) charge exchange. 

5. What is the cooling function? What are the major sources of heating and cooling in astrophysical gases. In your own words, briefly describe each.

6. With regard to the cooling function, what is the coronal assumption? Briefly compare and contrast the cooling functions for the coronal assumption only and for cooling functions that also include photoionization?  

7. In the regime T ≤ 105 K, at a given temperature, does the inclusion of photoionization heating yield a gas that is more ionized or less ionized than a purely collisional ionized gas? How does the cooling function change as the metallicity of the gas is increased?  Which three metals dominate for T ≤ 105.5 K? Which metals dominate for T ≥ 105.5 K?

8. How does the cooling time of a gas depend on the net cooling rate (and thus, cooling function)? Does the cooling time increase or decrease for higher metallicity gas?  Explain? In the regime T ≤ 105 K, when photoionization is taken into account, is the cooling more rapid in lower density gas or higher density gas?  Explain? 

Problems

1. Under construction