There have been a couple of pictures circulating on twitter apparently showing a yellowish ion trail. Seemed entirely possible to me, given the observations made on Hale-Bopp in 1997. I ventured that the colouration was probably real.
There’s an interesting subsection in the book Cometary Science by Crovisier and Encrenaz, CUP, 2000, pg 44 on the Hale-Bopp sodium tail, it has the phrase “the origin of cometary sodium is still a puzzle”. Seems still to be after 23 years!
I think it boils, literally and metaphorically!, down to the refractories in the nucleus, this may just be a quirk of the comets’ own formation. It’s there, so it must be in the minerals present.
In my spectroscopic meteor observations there are occasional meteors which exhibit very strong sodium emission also, I have often wondered if they somehow related to particular comets. The standard thinking seems to be that they are “fresh” meteoroids from which the sodium had still be be “boiled off”, so maybe yes, maybe no….
Do you have higher resolution spectra of the comet? I have seen nothing of the comet for a week and probably won’t for another week! The only thing I have for “stellar” spectroscopy now is a star analyser, I’ll give that a go if the opportunity presents itself.