PK204+04.1 in Monoceros

Kohoutek 2-2 was long thought to be a planetary nebula, but around 2013 astronomers began to conclude that it is more likely to be a region of ionized gas. A white dwarf star in the local nebula cloud has ionized Ha and OIII and mimicked the appearance of a planetary nebula. K2-2 is about seven arc minutes in diameter. I found distance estimates of 2400 and 1400 light years, and magnitude estimates of around 14.5. Otherwise there’s very little information about it. This is a bicolor Ha:OIII image, with RGB for stars.

Exposure: Total exposure time about 32.5 hours, 43:50 x 20 minutes Ha:OIII, plus 30 mins per channel for RGB stars. All bin 1x1. Data collected between October 2018 and March 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.5 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arsecs/pixel (50% of full 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 5nm Ha/SII, 3nm OIII, Type IIe LRGB
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 3.0.0.8
Guide SW: PHD2.6.3, 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 1.86

1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
StarAlign to register frames

2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop

3. Narrowband Linear Processing
Dynamic Background Extraction

4. Narrowband Stretching
Histo Trans x 3
Curves Trans
Second round of Dynamic Background Extraction
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred luminance frame as a mask to protect highlights
Mild Local Histogram Equalization to enhance nebula

5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans x 3
Boost saturation with Curves Trans
TGVDenoise

7. Color Combination
PixelMath: For color image, map Ha to Red, OIII to Green and Blue
PixelMath: For luminance image, max(Ha, OIII)
LRGB Combination of luminance and color images to create final narrowband image

8. Star Reduction and Background Removal on Narrowband Image
Create star masks for small, medium and large stars, then merge them in PixelMath with max command
Two iterations of star reduction: Morphological Transform to erode stars, Multiscale Linear Transform with bias to sharpen reduced stars
Add RGB stars to narrowband image with PixelMath and star mask

9. Final
Resample to 50% of scale
Save as JPG