Desperate times call for desperate measures, Ken
. It shouldn't be saturation inversion... I was careful to keep the histogram to about 225 or so.
I've had another play... when I reprocessed the yellow doublet, I found the image and spectrum was OK up until I normalised it in VSpec
... then the "absorption" artifact appeared.
Then I remembered that I wasn't converting from 2D to 1D in IRIS, so gave that a whirl and everything seems much better behaved. I'm still a bit suss about the red line though. As it was captured it appears very broad (broader than the others) and smooth like the original version and I'm not sure if I've created artifacts in the reprocess (or why I would have - I went through every frame manually to check the alignment
), but the other lines are better
.
Al.