Link to Inverted Images
This is the first detailed image of We 2-5 (PK 129-02 1, PN G129.2-02.0), which was entered by R. Weinberger in his 1977 compendium of 335 objects designated as possible, probable or true planetary nebulae since the closing of the 1967 Perek-Kohoutek PN catalog. The HASH planetary nebula database reports that in 2016 a spectra obtained with the 10-meter scope at Gran Canarias confirmed that We 2-5 is a PN. A central star was detected, but that star is much too faint to register in my images. The nebula is about 2.5 x 4 arcminutes in my image. I haven’t seen any magnitude estimate for it, but found a distance estimate of 2700 light years.
We 2-5 helps demonstrate why “hydrogen-alpha filter” is sometimes a misnomer. Amateurs usually image planetary nebulae with Ha and OIII filters. But my “Ha” filter is actually an Ha/nitrogen II filter. The dominant wavelength of NII is 658.3nm, very close to the 656.3nm wavelength of H-alpha, and because my filter has a 5nm bandpass, it allows both wavelengths to pass through. A 3nm Ha filter would block most of the NII light, which would be a problem for imaging many PNs, and this one in particular, since as shown by the GTC spectra the NII emission here is 7x the strength of the Ha emission. As the inverted narrowband images show, OIII emission is basically non-existent.
Exposure: Total exposure time about 38 hours, 103 x 20 minutes Ha, 36:36:35 x 2 minutes RGB. All bin 1x1. Data collected from August to December 2022.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated luminance 2.4 (Ha) and 2.2 (OIII) 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 6.2 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.18212 (SX Windows Drivers 15.26.50.450 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 4.2
Guide SW: PHD 2.6.11, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.6 SP1
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, 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, registration and integration with WBPP
2. Linear Processing
RGB Combination for RGB frames
Dynamic Background Extraction on narrowband and RGB
ImageSolve RGB, then run Spectrophotometric Color Calibration, using Average Spiral Galaxy white reference
BlurXterminator on narrowband and RGB
NoiseXterminator on narrowband and RGB
3. Lum/Narrowband Processing
Histo Trans x 3
Curves Trans
StarXterminator to create starless image
4. Colorization of Narrowband Image
Colorize to red with Curves Trans, pulling up red and pulling down blue and green
[for other NB images: Blend images in PixelMath, using Ha for red, OIII for green and blue
Curves Trans to shift nebula toward blue in narrowband image (pulling down green and pulling up blue, while keeping the LRGB balanced)]
Mild Localized Histogram Equalization to enhance internal contrast
Mild TGVDenoise
Final Curves Trans
5. RGB Processing
Histo Trans
Curves Trans to boost saturation
Histo Trans
Curves Trans for brightness
StarXTerminator to create starless and stars-only (star mask) images
PixelMath to subtract starless image from RGB image, adding a pedestal. This removes circular artifacts left over from flat calibration, which is caused by imaging with a moving-mirror SCT.
6. Image Combination
PixelMath to blend stars-only image and colorized narrowband image using formula ((1-$T)*(stars_only))+$T
In Photoshop, layer the nebula_plus_stars image onto the RGB image using a mask
7. Final
Final Histogram Transformation
ICC Profile Transform to sRGB
Save as JPG
