Kn63 was discovered around 2010 by Matthias Kronberger of the Deep Sky Hunters group. It's acquired the nickname “Medallion Nebula,” apparently because of its location near the neck of Orion. It’s about 6 arc minutes in diameter, and is so faint that it barely registers even in long exposure CCD images. OIII is much stronger than Ha (which isn’t saying much!). Link to single 20-minute OIII image. I found only two images other than the verification image taken with the Kitt Peak 2.1m reflector. The progenitor star appears to be the very faint blue star at center. This image uses OIII for luminance for the PN and maps Ha:OIII:OIII to R:G:B for color. The stars are separate RGB data.
Exposure: Total exposure time about 37 hours, 50:53 x 20 minutes Ha:OIII and 26:30:30 x 2 minutes RGB. All bin 1x1. Data collected September to November 2019.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.5 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/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 Type IIi LRG, Chroma B (the Chroma blue has a higher short wavelength cutoff than Astrodons, resulting in slightly less coma in blue stars)
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 3.1.0.457
Guide SW: PHD 2.6.7, 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 1.8.8:
1. Calibration
BatchPreProcessing with flats, bias, and darks, using Cosmetic Correction with master dark
Blink to preview and reject a few frames
Subframe Selector for Ha and OIII 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. Narrowband Linear Processing
Dynamic Background Extraction
No deconvolution – images were too faint to support any sharpening
4. Narrowband Stretching
Histo Trans x 2
Curves Trans
TGVDenoise
MultiscaleMedianTransform for noise reduction, using an inverted and blurred luminance mask
Local Histogram Equalization, using a range mask, to enhance contrast in the core
Additional curves, using a range mask to stretch only the nebula
TGVDenoise again
5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration
6. RGB Stretching
Histo Trans
Curves to boost saturation
Curves for contrast and more color boosting
TGVDenoise
Desaturate background, using an inverted range mask to protect the stars
7. Color Combination
Combine Ha and OIII in PixelMath using HOO palette to create color nebula image
Shift teal green to blue with Curves Trans
LRGB Combination, using OIII as luminance and HOO for color
StarNet to remove stars
8. Add Stars to Nebula
Using Using PixelMath, add RGB stars to starless nebula image
9. Final Repairs in Photoshop
Repair comatic halos: Create a color layer, then on medium-sized stars, Filter>Radial Blur around comatic stars
Save as TIFF and move back into PI
10. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Resample to 50% of scale
Save as JPG
