The Nebula
The Monkey Head Nebula is part of the diffuse nebula Sharpless Sh2-252, including the open star cluster NGC 2175 and the HII emission region, NGC 2174, and a molecular cloud. The extended H II region, over 60 light-years across, and 6,400 light years distant, is a large cloud of ionised gas where new stars are being formed. However, that powerful light and those stellar winds also erode all that gas and dust, so that in the future star formation will ultimately stop. The H II region is excited mostly by the bright luminous B star HD 42088 at the center. With a stellar type of O6.5V, this star is over 400,000 times more luminous than our Sun, with a surface temperature of over 38,000 Kelvin!

Because of the intense star forming, this nebula has been a favorite of the Hubble Telescope, making it to the HST 24th anniversary image. And there has been a lot of anticipation about what the JWST might find, though as far as I know no images have been captured.

Processing
I created the registered calibrated stacks for all 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 50% bin, a wipe (background extraction) and a digital development stretch. I then did a deconvolution for both images. For color balance, I did SHO into RGB channels as 40/60 SII/Ha, 70/30 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 tweaked in Photoshop.

In Photoshop I separated the nebulosity 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 some selective color and selective color saturation adjustments. In this case I was really pleased with the range of colors that I was able to pull out, including green. 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 screen function, linear dodge (add) made the stars too bright where there was nebulosity.

Insight Observatories data from AFIL-1

• Telescope: AG10 CDK F6.7 f=1665mm
• Mount: SkyWatcher EQ8RH
• Camera: ZWO ASI6200MM Pro
• Location: Lijiang, China (Gemini Observatory)
• Total of 126 images giving 27h 10 min integration
• B: 10 x 5 min = 50 min, G: 10 x 5 min = 50 min, R: 6 x 5 min = 30 min
• Ha: 20 x 15 min = 5 hr, OIII: 24 x 15 min = 6 hr, SII: 56 x 15m = 14 hr
• Imaged between 2022-03-08 and 2022-03-27.