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The Hole in the Trees Skybox | all galleries >> Deep Sky >> Planetary Nebulae > CTSS3 (Sh2-78)
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CTSS3 (Sh2-78)

Cappellaro Turatto Salvadori Sabbadin 3 in Aquila

CTSS3 (PN G046.8+03.8 ) was originally cataloged by Stewart Sharpless as an HII region, and is listed as Sh2-78 in his catalog. In 1990, an Italian team used a technique comparing the Palomar Observatory Sky Survey plate used by Sharpless with a new infrared survey plate, also from Palomar, and determined that Sh2-78 is actually a planetary nebula. This image seems to confirm that, showing hints of an “apple core” shape similar to M27, M76, and Abell 82. I’ve found only one other image of this object, on Dean Salman’s Sharpless Catalog site.

This is a bicolor Ha:OIII image, using Ha as luminance, with RGB for star colors.

Exposure: Total exposure time about 24.3 hours. 35:35 x 20 mins Ha:OIII, 10:10:10 x 2 mins RGB. All bin 1x1. Captured April to July 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: 1.2 arcsecs/pixel (50% reduction)

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
Camera: SXVR-H694, connected via SX ASCOM driver (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 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
Guide SW: PHD2.6.3, connected to guide cam via native SXV driver
Platesolving: PlateSolve 2, failover to local 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver

Processing Workflow by Workspace in PixInsight 1.85

1. Calibration
BatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark.

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

3. Narrowband Linear Processing
Dynamic Background Extraction
(No deconvolution – the nebulosity was too faint for sharpening to help)

4. Narrowband Stretching
Histogram Trans
Curves Trans
Noise Reduction with TGV Denoise and Multiscale Median Transform (following David Ault’s Astro Imaging Channel tutorial.)
(No Local Histogram Equalization on this data)

5. RGB Linear Processing
Dynamic Background Extraction
Photometric Color Calibration

6. RGB Stretching
Histo Trans and Curves Trans
Noise reduction with TGV Denoise

7. Color Combine
Linear Fit of OIII to Ha
Create color image with PixelMath: map narrowband Ha:OIII:(0.85OIII+0.15Ha) to R:G:B
LRGB Combination, using Ha as luminance on color image
Curves Trans to darken background

8. Star Reduction
Star removal, following David Ault’s technique:
Create separate Star Masks for small, medium and large stars, then merge with Pixel max operator
Morphological Transformation on masked image to erode stars (single iteration)
Multiscale Linear Transform with bias to slightly sharpen star cores
Additional pass of Multiscale Medium Transform with inverted luminance mask for noise reduction

9. Merge Narrowband and RGB Stars
Linear Fit of RGB stars image to narrowband image
Create star mask from RGB stars image
In Photoshop, use RGB Stars image as color layer with star mask
Increase saturation of RGB Stars layer
Radial blur on color layer to reduce comatic blue halos on stars near edges of FOV

10. Final
Downsize 50% and save as TIFF
Slight Curves Trans to darken background
ICC Profile to sRGB
Save as 100% quality JPG

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Sakib 29-Jul-2019 16:35
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