Thor's Helmet
Named after the Norse God’s headgear, this HII emission nebula is 12,000 light-years away. Personally I see an Octopus, with the bubble defining the Octopus’ head.

The bubble and the entire nebula are inflated by the central Wolf-Rayet star WR7 (HD 56925), indeed the bubble is described as a Wolf-Rayet Ring Nebula in the scientific literature. WR stars emit continuous streams of charged particles in their stellar winds. Here those particles  are colliding with interstellar molecular clouds. These collisions create the bow-shock front that defines the bubble, and ionizes the gas, which then fluoresces. This SHO image shows the SII, Hα and OIII fluorescence caused by that ionization. The nebula is also a continuum radio emitter, with a radio profile that reasonably matches the optical profile. There is also neutral gas including molecular CO. In total there is about 2200 solar masses of gas, spread over a volume of 30 light-years across.

Compared to our Sun, WR7 is about 280,000 times more luminous and 16 times more massive. A WR star is a late stage of evolution for a massive O-type star. WR stars have lost their hydrogen envelopes in the strong stellar wind emissions.  The WR phase is transient, with the next stage possibly a supernova in the cosmological-near future--so watch this space!

For those interested in more of the scientific details, these links are to a couple of interesting scientific articles.https://iopscience.iop.org/article/10.1086/300995/pdfhttps://arxiv.org/pdf/1708.08149.pdf

Processing
I created registered calibrated stacks for all of the  Ha, OIII, SII and RGB images using DeepSkyStacker. I composed two images in StarTools, one targeted at the SHO nebulosity and one targeted for the RGB stars. For both I did a wipe (background extraction) and a development stretch. I did an HDR enhancement for the SHO image, and deconvolution for both images. For color balance, I did SHO into RGB channels as 50/50 SII/Ha, 50/50 Ha/OIII, OIII. Note that despite the very long integration on SII, the signal was still low compared to Ha and OIII. For the RGB stars I did a simple color balance, final color was tweaking in Photoshop.

In Photoshop I separated the galaxies from the stars using StarXterminator for both images. For the SHO nebulosity I did an APF-R multi-scale unsharp mask and then I used did some selective color and selective saturation. I could not get a harmonious green to go with the other colors, so I went with a version that doesn't show a lot of green, which looked like the best option.  The last step was to do noise reduction using NoiseXterminator and PS Camera Raw. For the stars I also used some Selective Color and Selective Saturation adjustments. Stars were added back in as a layer with a linear dodge (add).

Data
Insight AFIL-1

• AG10 CDK F6.7 f=1665mm
• SkyWatcher EQ8RH
• FLI Proline 6303 Camera
• Lijiang, China (Gemini Observatory)

Total Exposure:  44 h

• SII = 900 s x 96 = 24 h, Ha=900 s x 36 = 9 h, OIII = 900 s x 37 = 9 h 15 m
• R = 6 x 300 s = 30 m, G = 7 x 300 s = 35 m, B =8 x 300 s = 40 m