Hi,
Sorry Andy, I forgot to add the response to your question, which is I’m not sure. This is at the hub of the “temperature problem”.
The curve should be the emission spectrum superimposed on a black body curve dependant on the physical temperature in the atmosphere. However in physics speak it is a “far from equlibrium process” This I believe is what leads to the catch 22 with the analysis based of line ratios. The get the correct line intensities you need to know the temperaure but to get the temperature you need to use the corrected line ratios. Somewhere an assumption has to be used to break the log jam. That’s how I read it anyhow. I can’t put my hand on the copy I have right now but there is a good book from the 60’s that give a good outline of whats going on in reasonably understandable terms. I’ll put the details on here shortly in case you want to get into it a bit more.
cheers,
Bill.