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An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Sat Nov 28, 2020 6:47 pm
by umasscrew39
One of the most peculiar emission nebulae and a fan favorite, the Bubble Nebula never ceases to amaze. This bright HII structure in the constellation Cassiopeia with its bubble created by the stellar wind from a massive hot, 8.7 magnitude young central star. The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. The star SAO 20575 is thought to have a mass of 10-40 Solar masses.

I decided to give my ASI294MM Pro a night off and switch to the ASI 2600MC Pro using the Optolong L-eXtreme duo (HA and OIII) 7nm bandwidth pass filter for the first time. Under Bortle 6 skies during 90%+ moon illumination and below average/average seeing, I thought the filter performed admirably well, especially on the C11"EdgeHD at prime optics, f/10.


Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Sat Nov 28, 2020 10:18 pm
by Menno555
Very nice!!
It's on my to-do list (of course) and then also with the L-eNhance.
About the image: I suspect there is more in it, the red is very dominant? With captures I did with the L-eNhance, there was more color in it. Could you share the stacked FITS or TIF with WeTransfer or something like that? I am curious on what I can get out of it (plus I have something astro to do then cause for weeks there's only clouds now :( )


Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Sun Nov 29, 2020 12:13 am
by umasscrew39
Well- there better not be more in it or the filter doesn't work and/or the nebula has changed. It is a dominate Ha structure (thus the red dominance) with very little OIII in it unlike other structures like the Veil Nebula. If you look carefully at it, the white wispy lines on the bubble itself are OIII. That is essentially it except for some thin outlining areas.

Also, I have already done this using separate Ha and OIII filters previously and posted viewtopic.php?f=16&t=3351. You can see more of OIII (i.e., white) in the HOO image. I have attached each channel separately here to see the huge difference. They are cropped and stretched to the same amount but you can zoom in, of course.

Finally, you can soften or dilute the red and I have done that like others using the L-enhance by creating a luminance channel from the red channel and then adding it back in. However, that only creates a different looking image- it does not bring more OIII out. This is actually one big reason why a lot of folks do not like these filters for structures that are heavily Ha dominate.
Bubble Nebula_OIII.jpg
Bubble Nebula_OIII.jpg (653.44 KiB) Viewed 334 times
Bubble Nebula_Ha.jpg
Bubble Nebula_Ha.jpg (531.03 KiB) Viewed 334 times

Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Sun Nov 29, 2020 12:54 am
by Menno555
You are correct of course ... I did mix up the L-Extreme and L-eNhance which I mentioned and have :oops: Plus I didn't know that that region is so Ha heavy.
Here still in doubt if I will go for the L-Extreme. I have the L-eNhance which is Ha, Hb and OII 24nm and I am in doubt if the Extreme with 7nm will perform "better". Part of that doubt also is that I did read on a few sites that the Extreme has a cleaner look in the blue channel in comparison with the Enhance.

Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Sun Nov 29, 2020 10:03 pm
by timh
Hi Bruce,

It is an amazing looking object -like a giant soap bubble. I have also been having a go at the bubble recently with an 8 inch Newt plus broad UHC filter plus AS1294 MC on my new CEM70 mount but have yet to match the nice sharp resolution of detail combined with sensitive detection of the nebula that you have there. Mind you I do get the benefit of some pretty diffraction spikes on the brighter stars, some bluish stars and whiter regions of reflection and/or OIII with the UHC. Presumably the seeing was at least OK when you took that despite the moon because the resolution and star size looks very good? I also love the wide-field image - I hadn't before clocked that M52 and the bubble are quite so close and the line up of both of them together makes for a very pleasant vista. There is something really quite satisfying about the bigger picture and understanding how things relate


Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Mon Nov 30, 2020 11:28 am
by umasscrew39
Hi Tim

Agree- the Bubble N is an amazing object. Would like to see your image from the Newt when you are done. The 249MC is a great camera. I had it for a long time before switching to the 2600MC. The broadband UHC LP filter will indeed give a different look of the Bubble N which is also very interesting and pleasing. I actually think the UHC and other broadband LP filters give a better look of the stars than the newer Ha/OIII-specific filters. I used it primarily on galaxies but it is an overall excellent LP filter. If you get a chance one day, try the Optolong L-Pro filter. It might bring more of the DSOs structure out while still surpassing LP. Nothing replaces dark skies, of course, but these filters do help as you have already observed.


Re: An Oldie but Goodie: NGC7635 The Bubble Nebula

Posted: Mon Nov 30, 2020 4:09 pm
by oopfan
Hi Bruce,

Awesome image! For inspiration (and humiliation) I visit Sara Wager's website. Here is her rendition of the Bubble:

Astro-Physics' website also shows a cyan bubble:

She did not specify, but I believe it is SHO. Plenty of SII highlights the farther from the center, and a mix of Ha and OIII (yielding Cyan) in the bubble and around it.

SII and OIII are almost always weaker than Ha, so how does she make Ha and OIII equivalent in strength in order to produce cyan? From her blog, she says that she stretches the stacks before combining them to achieve the desired effect. Therefore, she is stretching OIII to a greater extent than Ha. It is impossible to do with an L-eXtreme filter, but I understand that you can split the stack into three stacks, each for RGB, stretch them, and then recombine. Ha and SII, both being red, will show up in the red stack, but I am not certain where the OIII will go (green or blue?) Perhaps half goes to the green stack and the other goes to the blue stack? Either way, you probably want to stretch the green and blue stacks the same amount, and then recombine with the red stack. That should make your OIII roughly equivalent to your Ha.