The Ghost of Gamma Cas
IC 63 is an emission nebula being ionized by the bright Be star Gamma Cassiopeiae, just out of view to the upper right. This is a tricolor narrowband image.
Exposure: Total exposure time about 21.7 hours, 12:40:13 x 20 minutes SII:Ha:OIII. All bin 1x1. Captured from October to December 2016.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% reduction)
Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: CPC1100 fork mount on a Milburn deluxe wedge
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
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Celestron HD OAG
Guide cam: Lodestar (first generation). 1 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 1.85
1. Calibration
BatchPreProcessing with flats, darks and bias, using Cosmetic Correction with master dark
2. Stack and Mure Denoise
Blink to preview and reject a few frames
Subframe Selector to confirm selections
Image Integration
Mure Denoise
3. Linear Processing
Dynamic Crop
Dynamic Background Extraction
Deconvolution with Dynamic PSF and star mask (on Ha only)
4. Stretching
Histo Trans
Curves Trans
Noise Reduction following David Ault’s Astro Imaging Channel tutorial::
TGV Denoise
Aggressive Multiscale Median Transform to remove lumpiness in background, using an inverted and blurred range mask to protect highlights
5. Color merge
Merged narrowband channels in PixelMath, mapping SII:Ha:OIII to R:G:B
SCNR to shift green to yellow
Curves Trans to increase color saturation
Local Histogram Equalization in bright areas to enhance contrast
6. Star Halos and Size Reduction
Remove magenta star halos and casts in corners:
Invert image
SCNR on green
Re-invert image
Star Size Reduction:
Created and applied star mask following David Ault’s technique
Morph Trans using erosion to reduce stars (single iteration)
Mild Multiscale Linear Transform to sharpen stars
Mild Curves Transformation
7. Final
Photoshop: Create artificial flat and subtract it to remove rays from Gamma Cas
Downsize 50% and save as JPG
