SH2-206 (NGC 1491)

SH2-206 (also known as NGC 1491) is an emission nebula in constellation Perseus. The region is ionized by the star BD +50 886 which lies in a distance of about 10,700 ly (light years) from Earth (Gaia DR3 data). The stellar wind of this star interacts with the matter of a surrounding molecular cloud and forms a bubble, similar to the one of the Bubble Nebula but much smaller: about 60" (arcseconds) or 3 ly. The diameter of the ionized region of the molecular cloud is about 100 ly.

Click on the images for a full scale version.

SH2-206 (NGC 1491) (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 +50 886, the ionizing star, lies in the center of the bright region. The bubble is the small oval structure around the star.

SH2-206 (NGC 1491) 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: 0.64° × 0.5° (full view)
Date: 2019-2021
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): 8.0 h
[OIII] (3nm): 10.0 h
[SII] (3nm): 14.3 h
NIR: 0.7 h
Blue: 0.5 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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