Hi!
Great, I was quite curious about the quality of that star as well. Or maybe expressed more generally: why and how does reddening matter? OK, the actual spectrum does not match what we would expect – but as long as it is consistent as it is, could that not sufficient for a good ref-star? Just want to understand your reasoning there.
Moreover: I guess it would now also be possible to conclude (at least provisionally) that my problems with responseprofiles was related to the quality of the flat. My thinking in some detail: I use a camera with relatively low dynamic range (8 bits). This makes it challenging to capture the spectrum of a halogen lamp with color tempereature of about 2900 K so that I both get sufficient data in the blue end and avoid saturation in the most intense parts. I solved this now by turning the gain down to 0 (zero), getting maximum dyanmic range (I use a gain of 200 for capturing the faint stars like N Vul 2024 or SS Cyg at quiescence). With that setting, I get around 1400 counts in the lowest end. Previously, with higher gains, I had a count of 3-400. I suppose such low levels cause problems after dark reduction, since I am left with a very low count, very sensitive to low variations in the target spectrum (since I am dividing the target with the very faint flat). Makes sense?
SO I have learned a lot about flat production with these cameras (I have the ASI183mm), I think. Beyond learning more about how I need to check my intended ref-stars.
Magnus