Abell 43 in Ophiuchus

Abell 43 is a faint but intricate OIII-rich planetary located about 8500 light years away. Its progenitor star is a PG1159 star, a post-AGB star on its way to the white dwarf cooling sequence. Most PG1159 stars have used up their hydrogen, but a few, like this one, not only have hydrogen but have periodic pulsations. A study detected six significant pulsations in Abell 43’s central star, with periods between 2380 and 6075 seconds.

This image uses OIII colorized to blue for the nebula, layered onto an RGB starfield.

Exposure: Total exposure time about 13 hours, 34 x 20 mins OIII, 7:8:8 x 5 mins RGB. All
bin 1x1. Data collected from April to June 2023.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated OIII 2.4 arcsecs
Image scale at capture: 0.65 arcsecs/pixel
Scale of presentation: Full scale

Equipment:
Scope: 12” f/4 Newtonian with 3” Riccardi-Wynne coma corrector
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.2 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: ASI6200 MM, connected via NINA’s built-in driver
Filter wheel: ZWO 7x2” EFW
Filters: Chroma 50mm unmounted LRGB
Focuser/Rotator: Moonlite Nitecrawler WR35
OAG: ZWO OAG-L
Guide camera: ASI174MM, 4 second exposures
Automation SW: NINA 2, TheSkyX
Guide SW: PHD 2.6.11
ASCOM: ASCOM 6.6 SP1
Platesolving: ASTAP, failover to Astrometry.net
Processing Software: Pixinisight, Photoshop CS2

Processing Workflow by Workspace in PixInsight 1.8.9:

1. Processing
Calibration, weighting, registration and integration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
RGB Combination for RGB frames
Dynamic Background Extraction on luminance and RGB images
ImageSolve RGB, then run Spectrophotometric Color Calibration, using Average Spiral Galaxy white reference
Determine PSF using the FWHMEccentricity script, and enter this into BlurXTerminator
BlurXterminator using Correct First and manual PSF on luminance and RGB
NoiseXterminator on luminance and RGB

2. OIII Stretching
Histo Trans x 3
Curves Trans
No denoise necessary

3. RGB Stretching
Create a saturation mask: apply ScreenTransferFunction to the stretched luminance, and then to Histo Trans. Clip the mask with Histo Trans and blur slightly with Convolution.
Histo Trans x 2
Curves Trans to boost saturation, using the saturation mask to prevent spurious background colors from being boosted
Histo Trans
Curves Trans to brighten
TGVDenoise

4. Color Blending
Colorize nebulosity in OIII image to blue, using Curves Trans, by pulling up blue and pulling down red and green, and adjusting RGB as needed to maintain contrast and brightness
In Photoshop, layer blue nebula onto RGB starfield using mask

5. Final
Crop image
ICC Profile Transform to sRGB
Save final image as JPG