Theory of the Fireball

(3.21), it is small compared to the free-free absorption at' this low
frequency, except at T < 5000'. Its main effect is therefore to lower
the radiating temperature in the infrared somewhat.
Since the free-free transitions are the main cause of infrared
absorption, the electron density governs the temperature and density
dependence. For p/p, 2 10-1 and T 5 800o0, the ma& species of positive
4-
ions is NO The ionization energy of NO is 9-22 ev; tnerefore, the
electron density is roughly proportional to
From 6000 to 8000°, this gives a factor of about 10 in the electron
density, in accord with Gilmore's tables. Near 8000°, we' may write
approximately
-1.5
Writing p - pT , this gives
The temperature dependence
out about the same.
b. Visible
of the absorption in the visible will turn
In the visible and for temperatures below about 10,OOOo, the main
34
(4.3)
(4.4)