The Cone Nebula in Monoceros

The Cone Nebula is part of NGC 2264, a large HII region located 2700 light years away, which includes extended nebulosity and an open cluster. The Cone is an absorption nebula consisting of cold molecular hydrogen and dust in front of an emission nebula ionized by S Monocerotis, the brightest star in the open cluster, most of which is located outside of this field of view. The Cone is approximately seven light-years long.

Exposure: Total exposure time about 10 hours. 19 x 20 minutes Ha, 69:82:75 x 2 minutes RGB. All bin 1x1. Captured February – March 2020 and March – April 2021.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)

Seeing: FWHM of integrated Ha sub about 2.5 arcseconds
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% of original scale)

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon Type IIi LRGB, 5nm Ha and SII, 3nm OIII
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.1.0.558
Guide SW: PHD 2.6.9, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2

Processing Workflow by Workspace in PixInsight 1.8.8-12:

1. Calibration
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and reject a few frames
Rerun WBPP for weighting and registration

2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
Dynamic Crop

3. Ha Linear Processing
Dynamic Background Extraction on each channel
Deconvolution on Ha channel, using masks made in Photoshop so that only the brightest areas were sharpened.

4. Ha Stretching
Histo Trans x 2
Curves Trans
TGV Denoise to reduce fine-grained noise
Result = Ha Image

5. RGB Linear Processing
PixelMath to combine channels, blending 50% Ha and 50% Red into the red channel
Photometric Color Calibration

6. RGB Stretching for Nebula
Histo Trans
Curves to boost color saturation
Histo Trans
Make one copy and save as Stars Image
On original image, apply final Curves and save as Nebula Image

7. Processing for Stars
StarNet++ to create star mask from Stars Image

8. Photoshop to blend layers
Layer Ha Image as a luminance layer on top of Nebula Image Layer Stars Image on top as a color layer
Result is an HaRGB image, with Ha stars colorized by the RGB Stars Image
Use Spot Healing Brush on Nebula Image layer as necessary to remove any remaining star halos
Mild Denoise on darkest areas of Cone

8. Final
ICC Profile Transform to sRGB
Resample to 1/2 original scale
Save as JPG