The Corona Borealis Galaxy Cluster

Abell 2065 is the largest member of the Corona Borealis Supercluster, a group of galaxy clusters located about 1 billion light years away. The supercluster is made up of six or more clusters covering an area 330 million light years wide and 130 million deep, and contains as much as 120 quadrillion solar masses. Abell 2065 itself has about 400 galaxies.


Exposure: Total exposure time about 14.5 hours, 303:45:46:41 x 2 minutes LRGB. All bin 1x1. Data collected January to March 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.4 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.84 arcsecs/pixel (70% 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 and bias, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
Subframe Selector for luminance 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. This had basically no effect on the Lum channel, but worked well on the color channels.
RGB Combination for RGB frames
Dynamic Crop

3. Luminance Linear Processing
Dynamic Background Extraction
I skipped deconvolution. With targets this small it didn’t seem to make any difference at all.

4. Luminance Stretching
Histo Trans, Curves Trans
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. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans
Masked Stretch
Curves

7. Color Combination
LRGB Combination of luminance and RGB images

8. Star Reduction and Background Removal
Star masks for large stars
Morphological Transform to erode stars
Photoshop: Create an artificial flat by eliminating the remaining small stars with the Dust and Scratches filter
Subtract the artificial flat from the main image, masking out the galaxies
Use Radial Blur filter to obscure comatic blue halos on bright stars

9. Final
Final Histogram Transformation
Resample to 70% of scale
Save as JPG in Photoshop