Quote:
Originally Posted by Placidus
Sure looks like a faint halo in your image.
In general, it must be very difficult to know for sure that it's a halo, and not an effect of dodgy flats (doesn't look it in your case), or of processing. As a very retired researcher, I'd be very nervous about any processing that did anything at all that was regionally selective - handled different parts of the image differently.
I could imagine that a formal way of doing this might be to move the beastie to a completely different part of the chip for each sub, register, and then use analysis of variance to see whether say the outer half of the halo region is statistically significantly brighter than the background. You'd need to use robust statistical methods such as a rank transform (most robust) or winsorization (more informative) to ignore stars.
Another vague concern is glare. One could perhaps analyze the glare pattern around a bright star and control for this using radial distance as a covariate. (No, I'm not volunteering. It's been too long).
Having said all that, it sure looks real from the foot of the bed. And it looks very beautiful too. Well done.
Best,
Mike
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All valid approaches Mike...but what Steve and I are essentially doing is simply identifying that
something exists there and it's
basic shape & extent. Interpreting it more accurately is for the pro's in the end as they have the large aperture telescopes, multi million dollar detectors and the dark steady sites necessary for this bit (ala my faint dwarf galaxy discovery)
I (and I imagine Steve) have a good understanding of my imaging system glare profile around bright and dim objects, I have stretched many, many objects looking for faint strange halos (and jets
) so I know my system very well, if I suspect something I am pretty confident I have ruled out star glare, dodgy processing and flats. Perhaps though, when the faint halo is so faint and so uniform and so circular, such as with this one by Steve, it is indeed probably a little more difficult to rule out optical halation...? But I don't think the PN in this case is bright enough to cause the extent of what Steve has shown..?
All interesting discussion
Mike
