Link to inverted Ha and OIII images
StDr 27 (PNG 079.1-02.1) is the very faint arc near center. It was recently discovered by Xavier Strottner and Marcel Drechsler on an image collected as part of the INT Photometric Hydrogen Alpha Survey (IPHAS), which uses the 2.5-meter Isaac Newton Telescope on La Palma in the Canary Islands to collect 2-minute H-alpha images of the northern portion of the galactic plane. A matching survey (VPHAS+) is being made of the southern galactic plane. StDr 27 is currently listed as a candidate planetary nebula. The IPHAS image is extremely faint, and reveals little detail except a small arc that’s somewhat brighter than the rest of this Ha-suffused region. In my data, 4.3 hours of OIII showed no signal, so I didn’t use it in the final image.
Exposure: Total exposure time about 24 hours, 56 x 20 mins Ha, 17 x 20 mins OIII (not used in final), 35:35:35 x 2 minutes RGB. All bin 1x1. Data collected from June to August 2022.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated Ha and OIII luminance frames about 2.15 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 LRGB
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 Software: Pixinisight, Affinity Photo, Photoshop CS2
Processing Workflow by Workspace in PixInsight 1.8.9:
1. Calibration
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and reject a few frames
Weighting and registration with WBPP
2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop in both narrowband and RGB
Dynamic Background Extraction
3. Luminance Linear Processing
(No deconvolution on these images)
4. Narrowband Stretching and Star Removal
Histo Trans x 2
Remove stars with StarNet2
Curves Trans
TGV Denoise
Aggressive Multiscale Median Transform denoise (with an inverted luminance mask) to remove background lumpiness
5. RGB Linear Processing
Photometric Color Calibration, using Average Spiral Galaxy white reference
6. RGB Stretching and Star Extraction
Histo Trans x 2
Boost color saturation with Curves
Curves Trans
Create star mask with Starnet2
7. Colorization of Ha image
PixelMath to convert Ha to red, and set green and blue at background level of Ha (0.12)
Curves Trans to brighten
Heavy Multiscale Median Transform on selected areas (using a mask created in Photoshop) to reduce lumpiness in background
8. Image Combination
PixelMath using the formula ((1-$T)*(star_mask))+$T to add stars into colorized Ha nebula image
9. Final
Final Histogram Transformation to darken slightly
ICC Profile Transform to sRGB
Resample at 50% scale
Save as JPG
