4.4. Testcase #4

We now illustrate how to use PopRatio to calculate collisionally excited emission line intensity ratios.

As an example we take the UV intercombination multiplet 2s2p^{2 4}P -> 2s²2p ²P^o of C II at 2325 Å. Intensities ratios of lines belonging to this multiplet may serve as a useful indicator of electronic densities in the range 10⁷ n_e 10¹⁰ cm^-3 [23, 24]. These lines have been observed in the spectra of a variety of astronomical objects: planetary nebulae [25], giant stars [26, 27], symbiotic stars [28] and in the solar chromosphere and transition region [29].

The emissivity of a line is given by [4]:

(23)

We calculate the following emissivity ratios as a function of electronic density:

(24)

We take into account collisions by electrons and protons and fluorescence induced by a black body radiation field of temperature T_* = 4000K attenuated by a geometric dilution factor f = 0.5 (which might be representative of a stellar chromosphere).

In the high density limit function LTEDEV is called to show that the level populations differ from LTE conditions by less than 0.4%.

To run this testcase the user must include the black body radiation field in the body of function URAD in module POPRATIO:

urad = Planck(4.0E3_WP,c/lambda*1.0E8_WP)