SH2-101 (Tulip Nebula)

SH2-101 (also known as Tulip Nebula) is an emission nebula in constellation Cygnus. It is assumed that the nebula is ionized by the Cygnus OB3 association which extends within a distance of about 5000 to 8000 light-years from Earth, see [1]. One famous member of this association is HDE 226868 which forms a binary system with the suspected black hole Cygnus X-1.

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SH2-101 (Tulip 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.
SH2-101 (Tulip Nebula) in false colors (OHS)
Same view as above, but [SII] and [OIII] are swapped in order to improve the visibility of the oxygen structures (reddish).

According to [2] the red structure on (and partially cropped by) the right boundary is caused by a jet interacting with the interstellar medium. (The red color means high [OIII]/H-alpha ratio compared to SH2-101.) The jet comes from Cygnus X-1 which forms a binary system with HDE 226868, the brighter/lower star of the two bright stars near the bottom right corner. The black hole accrets matter from its companion and some of the gas which does not fall into the black hole is shot out in form of these jets.

Image data

FOV: 0.67° × 0.5°
Date: 2019-2020
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): 8.3 h
[OIII] (3nm): 10.1 h
[SII] (3nm): 12.2 h
NIR: 0.6 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


  1. Anjali Rao, Poshak Gandhi, Christian Knigge, John A Paice, Nathan W C Leigh, Douglas Boubert. (2020). "Kinematic study of the association Cyg OB3 with Gaia DR2". Monthly Notices of the Royal Astronomical Society. 495 (1): 1491–1500, Astronomy & Astrophysics 630: A137.
  2. D. M. Russell, R. P. Fender, E. Gallo, C. R. Kaiser. (2007). "The jet-powered optical nebula of Cygnus X–1". Monthly Notices of the Royal Astronomical Society. 376 (3): 1341–1349

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