[Placidus (Mike and Trish)]

Originally Posted by Atmos

That’s a really interesting methodology MnT, not something I’d considered doing but it’s worked well!
What makes it interesting is that it’s purple in the SHO image and OIII in colour in RGB which is suggestive of both SII and OIII emissions. If it was purely reflection nebulosity then it shouldn’t show up in SHO at all like other reflection nebula.

Thanks Colin! Totally agree. The one slight gloss is that if you hold an OIII filter up to continuum light, then some tiny percentage of it does get through. Hence the some ridiculously tiny percentage of the light from a reflection nebula (say 3%) does get through an OIII filter.

Originally Posted by Atmos

It’s a bit difficult to see in these images but I’m assuming it still has the “squiggles” in Version C?

Yes. Big version here. I've edited the original post to include this.

Originally Posted by Atmos

The overall look around that star appears to be reflection nebula after the SHO has been removed so I think we can say that it’s a given. It’s a bright energetic star so it’s not surprising to see reflection nebulosity around it.

It also cannot be purely reflection otherwise it wouldn’t appear so strong in OII and SII. As to what could cause that process, it’s still racking my brain a bit. It’s definitely suggestive of high energy processes in the past with SII but a decent NII emission isn’t suggested by the blue colour. In pure RGB it still looks like a very strong OIII emission.

Again, a well-reasoned argument, and we thank you for taking the time to think about it. We reckon astrophotography is all the richer if one stops and ponders what one is actually looking at. Titanic forces at play.

We still can't quite see what the physics of the "lightning bolts" might be, but they do seem to involve both emission nebulosity and reflection nebulosity. A guess might be that there is foreground emission nebulosity with background reflection nebulosity. We need a resident super-guru, to give the answer in the back of the book.

Originally Posted by codemonkey

Super cool, M&T! Like Colin, not something I'd ever considered.

What did you use to produce D?

Thanks Lee. We removed the stars using our own in-house software package "GoodLook". A few mouse clicks and you find all the stars (bandpass filter, find the local peaks, select those with a high correlation with a stellar template). Then you use bilinear polynomial regression to try to guess what would have been "under" the star if it weren't there, given the immediate background. It works superbly except for the biggest, baddest, burned out stars, of which there were two in this image.

We tried leaving out this star-removing step, and adding the RGB|SHO directly into the HSO image, but it didn't work because the OIII and SII fringes around the SHO stars are so much bigger than the RGB stars.

Originally Posted by multiweb

Fascinating. And a great result to boot.

Thanks muchly Marc! I guess we achieved our original goal of making an NB image with halfway decent RGB stars, by using multiple linear regression to remove SHO "contamination" from the RGB image, and on the way, realized that Gabriela Mistral must include a lot of reflection nebulosity. That was a bit of an adventure, almost as good as growing potatoes.

Best,
Mike