SH2-162 (NGC 7635, Bubble Nebula)

SH2-162 (also known as NGC 7635 or Bubble Nebula) is an emission nebula in constellation Cassiopeia. The nebula consists in a bubble with an apparent diameter of about 200" (arcseconds) and a surrounding molecular cloud. The region is ionized by the hot young O-type star BD +60 2522. The bubble is formed by the interaction of the stellar wind of this star with the matter of the molecular cloud. The central star lies at a distance of about 9800 ly from Earth (Gaia DR3 data).

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SH2-162 (NGC 7635, Bubble Nebula) in false colors (SHO)
This image is a false color composite where [SII] is mapped to red, H-alpha is mapped to green and [OIII] is mapped to blue. Stars are partially subtracted using continuum images.

BD +60 2522, the ionizing star which stellar wind forms the bubble, is the brighter star in the bubble next to the saturated area.

SH2-162 (NGC 7635, Bubble Nebula) in false colors (OHS)
Same view as above, but [SII] and [OIII] are swapped in order to show more details of the oxygen structures (reddish).

Image data

FOV: 0.67° × 0.51° (full view)
Date: 2018-2021
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): 8.3 h
[OIII] (3nm): 10.0 h
[SII] (3nm): 12.6 h
NIR: 1.0 h
Blue: 0.6 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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