RCW 75 Elephant Trunk Nebula in NB RGB

[Bassnut]

Hi Guys

Also known as Gum 48a. In Centaurus.
Ha tainted red and RGB blend.
No OIII or SII, but quite a bit of NII, but It was identical to Ha, so not used.
Would be interesting to know why Ha and NII, but no OIII or SII

Big here (https://fredsastro.smugmug.com/Photography/Astrophotography-1/i-kQzJq44/A)

Taken on an RCOS 10" RC Scope at f9, SBIG STXL6303E Camera and PME mount at itelescopes Siding Spring Observatory.
Processed with CCDstack, Star Tools and Photoshop. 37 hrs Total exposure time.
Ha RGB

Ha 34hrs, 40min subs bin1. RGB 3 hrs, 20min subs bin1

[RickS]

Nice one, Fred! Shame that, unlike the northern Elephant Trunk, there's not some interesting Oiii and Sii to contribute to a colour NB image. On the plus side it is an object that hasn't been imaged to death :lol:

[Placidus]

Intriguing and different, Fred. Totally new to me. Wonderfully presented.

In answer to your question, why is there H-alpha and NII (identical to the H-alpha) but no OIII or SII, my guess would be:

(1) The NII image is actually H-alpha that has struggled through the NII filter. The bandpass of a 3nM NII filter overlaps that of a 3nM H-alpha filter.

(2) This is a youngish star-forming region, in which either (a) there are as yet no really hot young stars out and about nearby that can ionize oxygen and sulphur, or (b) there has been little supernova activity so no shock front energy to do the job, and/or there is not so very much oxygen and sulphur released from within, or (c) where there is oxygen and sulphur, the gas pressure is too high for the forbidden lines to form, or (d) most likely, all of the above.

You've captured much beautiful blue glow. Since you've shown it's not OIII, it is almost certainly reflection nebulosity.

Excellent!

Very best,
Mike

[strongmanmike]

Great shot Fred, quite reminiscent of the popular northern Elephants Trunk neb inside IC1396 in Cepheus. Also reminds me of a Cobra or the electronic eye in the original War of the Worlds movie. Nice work on a rarely imaged target :thumbsup:

Mike

[marc4darkskies]

Nice one Fred! :thumbsup: This is a dim and difficult target!!

You inspired me to (push) process the pathetically small amount of Ha data I got back in May 2015. Weather and camera issues prevented me from finishing but it's on my todo list (along with the others in my "Work-In-Progress" folder!! You can see it here (http://www.pbase.com/gailmarc/work_in_progress).

[gregbradley]

A new object! Great, I haven't seen this one before. A fabulous image.

34 hours of Ha, gawd you're patient.

Greg.

[Bassnut]

Thanks Rick. Yes, I still find rarely imaged southern targets even when I think theres none left :P



Cheers Mike.I had to go back and check the 3nm filter specs, and yes, Ha does leak 15% NII. Not only that, NII has 2 spectral lines, either side of Ha ! " NII emits most strongly at 658.4 nm (and weakly at 653.8 nm)".
On reading the literature, they did mention the blue was reflection nebulosity. Thanks for the explanation, I should read up more on what Im looking at :D.



Thanks Mike. Your catching that description disease a certain other Mike has, seems to be contageous :lol:



Thanks Marcus. It is very dim!. I didnt want to complain, but it was hard to process. Your pic is pretty good :thumbsup:, with a bit of RGB you could finish it off the way it is !.



Thanks Greg. Its been done a few times by IIS guys, mostly wide field. Jase springs to mind.