Hi David
“Including the 3946.097A line gives a considerably worse fit at the blue end.”
I have had a look at the high resolution echelle spectrum of the lamp that Shelyak use in Richard Walker’s atlas. (plate 98 order 57) The 3946.097 Ar line that ISIS uses for a lamp line fit with the ALPY is in fact a close triplet 3946.097, 3947.505, 3948.979 so definitely incorrect. I don’t think this is connected with what John is seeing but I suspect this may be the cause of my increasing error towards the blue using just the lamp calibration.
I took a spectrum of MILES star HD206165 last night to experiment with. It is a B2i star so lots of narrow H and He lines which hopefully should show up any errors
Cheers
Robin