The two images below highlight stuff that shouldn't be there in Thor's Helmet. I wonder if it is a reflection, or some kind of light leak. It only seems to happen with my Ha filter.
I think you are showing me calibrated data. Is the issue detectable in your raw data?
Does your flat have a dark thing in these positions?
My guess is that this stuff is from your flat field having some gunk that is creating an inverted image.
But of course...I do not have enough information. You need to tease out where it is coming from by looking at your darks, flats (especially) and raw data compared to calibrated data.
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