The NGC 80 Galaxy Group in Andromeda

The NGC 80 group is located about 260 million light years away, which likely makes it a member of the Perseus-Pisces Supercluster, a filament of galaxy clusters covering 40 degrees of the sky. The elongated spiral just below center is NGC 90, which is interacting with NGC 93 just below it and exhibits two highly elongated and distorted spiral arms with bright blue star clusters indicative of star formation, likely caused by the interaction with its neighbor, which is only 2 million light years away. NGC 85 and IC1546, on the other hand, are separated by about 20 million light years apart. NGC 90 and NGC 93 are also cataloged as Arp 65.

Exposure: Total exposure time about 8.3 hours, 164:27:28:27 x 2 mins L:R:G:B. All bin 1x1. Captured October 2018 to January 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: FWHM of best subs about 2 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
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
RGB Combination for RGB frames
Dynamic Crop

3. Luminance Linear Processing
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask for deringing support (on lum channel only, and only on cores of a few bright galaxies)

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
Boost saturation on stars with Curves Trans
Curves Trans
TGVDenoise
Make a separate version with lower stretching for stars only (“Stars” image)

7. Color Combination
LRGB Combination to create “Galaxies” image

8. Star Removal
Star removal from Galaxies image using star masks, Morphological Transform, and Multiscale Median Transform on the residual layer. See David Ault’s technique.

9. Photoshop: Background Removal
Create an artificial flat by eliminating the remaining small stars with the Dust and Scratches filter
Subtract the artificial flat from the Galaxies image, masking all of the galaxies (PITA!)
Use Radial Blur filter on a color layer to obscure comatic blue halos on bright stars

10. Merge Images
With PixelMath max command, merge Stars and Galaxies images
Final Histogram Transformation
Save to Web as JPG