SH2-105 (NGC 6888, Crescent Nebula)

SH2-105 (also known as NGC 6888 or Crescent Nebula) is an emission nebula in constellation Cygnus which ionized by the Wolf-Rayet star WR 136 which lies in a distance of about 5600 ly from earth (according to GAIA DR3). That kind of stars are supernova progenitors. At least a part of the gas was ejected when the star became a red giant. The apparent diameter of this nebula is about 17' (arcminutes).

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SH2-105 (NGC 6888, Crescent Nebula)
This image is a false color visualization where H-alpha is mapped to red, [OIII] is mapped to green and a mixture of both channels (1.5 times [OIII] minus 0.2 times H-alpha) is mapped to blue. Stars are partially subtracted using continuum images.
SH2-105 (NGC 6888, Crescent Nebula)
This pseudo color view is composed from H-alpha light (shown dark red to yellow) and [OIII] light (shown dark blue to cyan).
SH2-105 (NGC 6888, Crescent Nebula)
Compared to the previous image, here H-alpha (shown dark blue to cyan) and [OIII] (shown dark red to yellow) are swapped. This unusual view better visualizes the oxygen structures which show more details than the hydrogen structures.

Image data

FOV: 0.67° × 0.51° (full view)
Date: 2018-2020
Location: Pulsnitz, Germany
Instrument: 400mm Newton at f=1520mm
Camera Sensor: Panasonic MN34230
Orientation: North is up (approximately)
Scale: 0.8 arcsec/pixel (at full resolution)
Total exposure times:
H-alpha (3nm): 12.3 h
[OIII] (3nm): 18.2 h
NIR: 0.6 h
Blue: 0.9 h

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

  1. Bias correction, photon counting
  2. Dark current subtraction, flatfield correction, noise estimation
  3. Alignment and brightness calibration using stars from reference image
  4. Stacking with masking unlikely values and background correction
  5. Extracting stars from the emission line images using information from continuum images
  6. Denoising and deconvolution both components (stars and residual)
  7. RGB-composition
  8. Dynamic range compression using non-linear high-pass filter
  9. Tonal curve correction

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