ASTRONOMY 402T – Spring 2018
Problems for Tutorial Week #7

PART A

1. a) Explain in detail why the intensity ratios of density-indicating pairs like [S II] λλ6717/6731 and [O II] λλ3729/3726, in fact do allow us to calculate the nebular density.

b) Consider the density-indicating pairs [O II] λλ3729/3726 and [Ar IV] λλ4711/4740. Draw and label their energy level diagrams. In what density regimes are the [O II] and the [Ar IV] pairs useful?

c) Why is there a particular density regime for each pair, and what determines these regimes?

2.  Explain in detail why the intensity ratios of temperature-indicating pairs like [O III] λλ4363/5007 and [N II] λλ5755/6584, in fact do allow us to calculate the temperature. Draw and label their energy level diagram.

3. Discuss the ranges of temperature and density on H II regions and in planetary nebulae. How do they compare, and why?

PART B

Do the PN Gallery “Determining the Gas Density in Planetary Nebulae” exercise:

http://web.williams.edu/Astronomy/research/PN/nebulae/exercise3.php