The Cat's Eye Nebula in Draco

NGC 6543 is located about 3300 light years away. The brilliant core of the nebula is about 16 x 20 arcsecs, and the halo covers about five arcminutes. The central white dwarf star has about one solar mass, having shed four solar masses during its lifetime. I also made a 2x enlargement of various versions of the core. The barred spiral galaxy at left is NGC 6552, at about 370 million light years. It's of interest to astronomers because it hosts a water maser. At right is 2MASX J17572815+6638204, at 650 million light years. I found no redshifts for any other background galaxies.

This is a bicolor Ha/OIII image, using 2 minute and 20 minute exposures. Four separate processings – core, core extensions, concentric rings (all using the 2 minute exposures), and halo (20 minute exposures) – were made and then composited to make the final image. 30 second RGB exposures were used for the star colors. Ha was used as luminance for the galaxies.

Exposure: Total exposure time about 35 hours, 44:47 x 20 minutes Ha:OIII, 107:106 x 2 minutes Ha:OIII, 30:12:22 x 30 secs RGB for stars, all bin 1x1. Halo data was collected from 2016 to 2018, core data in early 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.3 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.6 arsecs/pixel

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 3.0.3.169
Guide SW: PHD2.6.6, 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
Subframe Selector to confirm selections and weight by FWHM and SNR
StarAlign to register frames

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

3. Linear Processing
Dynamic Background Extraction
Deconvolution on core images
Sharpening on core images using Multiscale Linear Transform, set to starlet transform and using large scale transfer function/hyperbolic

4. Stretching
Histo Trans
Curves Trans
(making five separate sets of images: Core, Core Extensions, Concentric Rings, Halo, and RGB Stars)
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred luminance frame as a mask to protect highlights

5. Channel Blending
PixelMath, mapping channels to:
Red: Ha
Green: OIII
Blue: OIII*0.85 + Ha*0.15
Color shift on Halo image:
Extract luminance image
Color Mask to create cyan mask, then curves to boost blue and reduce green
LRGB Combination to add luminance image back into colored halo

6. Blend Core and Halo Images
Pixinsight: create range masks for core and core extensions images
Photoshop:
Using the range masks, layer core, core extensions, and concentric rings images together into single “core and rings” image
In halo image, use Magic Wand to select blown-out core, then expand the selection a few pixels
Using selection area as a mask, use Curves to darken core down to zero
Layer “core and rings” image into halo image, using circular gradient mask

7. Star Reduction
Create star mask following David Ault’s technique
Morph Trans to reduce stars
Multiscale Median Transform to slightly sharpen stars

8. RGB Star Colors
Photoshop: Using star mask created in PI in Step 7, layer RGB Stars as a color layer onto Core and Halo image

9. Boost Background Galaxies:
Create range mask, edit with Clone tool to remove everything but background galaxies
Convolution to blur mask
Curves trans, using mask, to stretch galaxies

10. Final
Histogram Transformation to brighten core
sRGB
Save as JPG