dust donut ?

Forums Spectroscopy Anomolous absorption line? dust donut ?

Robin Leadbeater

Hi Kevin,

I suggest checking your flat image in this area. This double line effect looks typical of that produced by a dust donut. Take a profile across the flat at the location of the spectrum.  I was discussing with Jack Martin the other day who saw something similar (at a different location). It turned out to be a defect visible in  the flat which for some reason we don’t quite understand was not corrected by the flat (The defect was weaker in the flat than in the image)