Link to inverted images
NGC 1514 was discovered by William Herschel on November 13, 1790, and it led him to revise his view of the universe. He previously believed that all nebulae consisted of masses of stars too remote to resolve, but now here was a single star "surrounded with a faintly luminous atmosphere." He concluded: "Our judgement I may venture to say, will be, that the nebulosity about the star is not of a starry nature."
Distance estimates for this nebula range from 650–980 light years. It’s about 10th magnitude, with an inner shell measuring about 2 arcminutes and an outer halo of about 3 arcmins. The central star is actually a binary. The visible component is an A0 main sequence star, with the progenitor star in a nine-year orbit around it. Some images show a red reflection nebula near the bright orange star (HD 26125), but the light pollution at my site is far too strong for that to show here.
Taking into account the varying color sensitivity of the sensor, the OIII signal appears to be only about 20% stronger than the Ha/NII signal. However, the RGB data shows the blue-green color typical of an OIII-dominant PN. This image uses RGB data for the stars and for the color in the nebula. Luminance for the nebula is a combination of narrowband Ha and OIII data.
Exposure: Total exposure time 24.1 hours, 34:25 x 20 minutes Ha:OIII and 50:50:33 x 2 minutes R:G:B. All bin 1x1. Data collected from November 2020 to January 2021.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated narrowband images around 2.27 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.88 arcsecs/pixel (67% of original 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 1.8.8:
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
Dynamic Background Extraction
For the narrowband images, I then integrated the Ha and OIII integrated images into a single Ha-OIII image. The combined image had slightly better SNR than either of the separate images. To do this, I had to create copies of each image, because ImageIntegration in PI requires at least three frames to run. I set ImInt to use noise evaluation as the weighting factor.
3. Narrowband Linear Processing
Deconvolution:
Dynamic PSF to create PSF image
Deconvolution, using a mask created in Photoshop to sharpen selected areas only
4. Narrowband Stretching
On each image: Histo Trans x 2
Curves Trans
Additional deconvolution, with parametric PSF
TGV Denoise
5. RGB Linear Processing
Photometric Color Calibration, using Average Spiral Galaxy white reference
6. RGB Stretching
Histo Trans x 2
Curves Trans
7. Color Combination
LRGB Combination of Ha-OIII as luminance and RGB as color = Nebula Image
Curves Trans to boost color saturation on Nebula Image
StarNet++ to remove stars from Nebula Image
Range mask on Nebula Image to highlight only the nebula
Apply the mask to the RGB starfield, then use PixelMath max command to combine the starless Nebula Image and the RGB stars image. The mask prevents the nebula background (about 0.06) from being added to the RGB starfield background (about 0.07). A background of 0.06 also was subtracted from the nebula image in the PixelMath merge operation: $T+(Nebula-0.06).
8. Background Subtraction
a. Create an image of the background:
1. StarNet++ to create a starless image. I cleaned this up a bit in Photoshop, using the spot healing brush to remove the nebula and a few leftover star halos.
2. Apply Convolution to the starless image so that noise is not removed during the subtraction process
b. Subtract the background image from the original image in PixelMath to remove remaining gradients and any messy clumps in the background, applying an offset so that the background is not pure black: ($T+0.06)-BackgroundImage
9.
Final
Resample to 67% of original
ICC Profile Transform to sRGB
Save as JPG
