Two-photon calculation?

[jwreep]

The calculation of the two-photon continuum does not seem to match the equation in the CHIANTI user's guide:

As far as I can tell, the equation as programmed (in ChiantiPy or IDL) is:

and $A_{\text{sum}} = 1$ for helium-like ions.

It might be that the mismatch is in the guide's definition of $\phi(y)$? It's not stated what that definition is (nor is it in the Young et al paper). Could this please be clarified? What is the full form of the equation used by Chianti and what is the appropriate reference?

Additionally, what is the $A_{\text{sum}}$ term found in the hydrogen-like data files? What are its units? I have not been able to find any papers that reference it.

Any help would be greatly appreciated!

[jwreep]

The $A_{\text{sum}}$ term appears to be a normalization factor of the integral of $\phi(y)$ (or $\psi(y)$ in the code). See here.. Confirmation would be appreciated, though!