Abell 19 is a very faint (magnitude 17), small (about 1 arcminute), and old planetary nebula located about 7500 light years away. Other than survey images, this is the only image I know of. The star at the center of the nebula may not be the progenitor star, since PN central stars are usually blue and this one is rather yellow. This image uses Ha for luminance for the PN and the background nebulosity, and maps Ha:OIII:OIII to R:G:B for color. The stars are separate RGB data.
Exposure: Total exposure time about 31.7 hours, 41:51 x 20 minutes Ha:OIII and 9:9:9 x 2 minutes RGB. All bin 1x1. Data collected November 2019 to February 2020.
Light pollution: Bortle 7-8 (white zone, NELM about 4.5)
Seeing: Average FWHM of subs around 2.6 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.9 arcsecs/pixel (67% 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 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
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 3
Curves Trans
StarNet to remove stars
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
Local Histogram Equalization, inverting the range mask and a high kernel radius, to enhance contrast in the background nebulosity
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
7. Color Combination
Combine Ha and OIII in PixelMath using HOO palette to create color nebula image
LRGB Combination, using Ha as luminance and HOO for color
8. Add Stars to Nebula
Shrink RGB stars with a mask for larger stars, Morphological Transform, and Curves Transform to restore brightness after fading with MT
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
Use dodge, burn and desaturation sponge tools to eliminate remaining coma
Save as TIFF and move back into PI
9. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Resample to 67% of scale
Save as JPG
