Heckathorn Fesen Gull 1 in Cassiopeia

HFG1 (PK 136+05, PN G136.3+05.5) is about 14th magnitude and 8.5 arc minutes in diameter. It was discovered in the Milky Way Emission Line Study in 1982. Its magnitude 14.5 central star, V664 Cas, is a close binary consisting of a white dwarf and a Sun-like star, which are only a few million kilometers apart and are orbiting each other every 14 hours. V664 Cas (the relatively bright star located at the lower left edge of the clear patch in the center of the nebula) is moving through the interstellar medium with a velocity of 35 km/second, producing a bluish bowshock and leaving a trail of gas in its wake. The distance to HFG1 has been estimated at either 1600 or 2300 light years away. This is a bicolor narrowband image, mapping Ha:OIII:OIII to R:G:B, with RGB stars added to the starless nebula in Pixinsight.


Exposure: Total exposure time about 25.3 hours. 41:26 x 20 minutes Ha:OIII, 20:20:20 x 2 minutes RGB. All bin 1x1. Captured September to December 2019.
Light pollution: SQM ~18.2 (Red/white zone border, Bortle 7-8, NELM at zenith about 4.5)
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.8 arcsecs/pixel (33% size)

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer imaging at f5.7
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
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep with driver version 6.0.7
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.0.3.169
Guide SW: PHD2.6.3, 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 1.88

1. Calibration
Weighted BatchPreProcessing with flats, darks, and bias, using Cosmetic Correction and weighting by SNR and FWHM.

2. Stack and Mure Denoise
Blink to preview frames and remove some bad images
Image Integration
Mure Noise Reduction on each channel
Channel Combination to merge RGB channels
Dynamic Crop

3. Narrowband Linear Processing
Dynamic Background Extraction

4. Narrowband Stretching
Histogram Trans x 2
Curves Trans
Noise Reduction with TGV Denoise and Multiscale Median Transform (following David Ault’s Astro Imaging Channel tutorial.)

5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans x 2
Create star mask with Advanced Star Mask script
Boost saturation of stars slightly with Curves, using the mask

7. Color Combine
LRGB Combination using Ha for luminance, and boosting saturation

8. Merge Narrowband and RGB Stars
Merged narrowband channels in PixelMath, mapping Ha:OIII:OIII to R:G:B
Created a mask with the OIII layer, and used Curves to shift cyan/teal to blue
Remove stars from nebula with StarNet
Add stars to nebula: create star mask from RGB stars image, apply mask to nebula image, then use Pixinsight to add stars to nebula

9. Final
Resample to 33% scale
ICC Profile to sRGB
Save as 100% quality JPG