NGC 1579 (SH2-122)

NGC 1579, also known as SH2-122, is a reflection and emission nebula in the constellation Perseus. It is primarily illuminated and ionized by the emission line star LkHα 101, at a distance of about 2000 light-years (620 pc). The apparent diameter of the ionized region is about 0.25°, corresponding to a true diameter of roughly 8.7 light-years (2.7 pc). NGC 1579 is partially obscured by another molecular cloud located about 300 light-years (90 pc) in the foreground and which is responsible for several reflection nebulae around young blue stars.

NGC 1579 (SH2-122) in H-alpha and continuum
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This image is a false color composite where Hα (including red continuum) is mapped to red, blue is mapped to green and near infrared is mapped to blue. Stars are partially subtracted to improve the visibility of the nebulae.

The emission region appears red. The reflection nebulae appear mostly bluish, due to the color of the illuminating stars (also see the description of the next image).

NGC 1579 (SH2-122) in continuum
Hα: off
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In both images, NIR (near infrared) is mapped to red, red is mapped to green and blue is mapped to blue. In the version with Hα, that emission line is added to the red channel. Stars are partially subtracted to improve the visibility of the nebulae.

The primary illumination and ionization source of NGC 1579 (SH2-122) is the highly reddened emission line star LkHα 101, located about 2000 light-years away (620 pc, according to Gaia DR3). The dust responsible for the reddening (an effect of Rayleigh scattering, which is stronger at shorter wavelengths) at least partially belongs to a molecular cloud located about 300 light-years in the foreground. The distance of this molecular cloud is known from precise Gaia DR3 parallax measurements of the stars illuminating the bluish reflection nebulae, all of which lie at about 1700 light-years (530 pc).

Image data

FOV (full view in the JavaScript viewer): 0.60° × 0.44°
Position (J2000): RA: 4h30m20s; DEC: 35°20′
Date: 2019-2023
Location: Pulsnitz, Germany
Instrument: 400mm Newton at f=1520mm
Camera Sensor: Panasonic MN34230 (all but red), Sony IMX455 (red)
Orientation: North is up
Scale: 0.8 arcsec/pixel (at full resolution)
Total exposure times:
Hα (3 nm): 14.2 h
Near infrared: 6.3 h
Red (SDSS R' + 400-650 nm band-pass): 4.7 h
Blue: 4.5 h

Image processing

All image processing steps are deterministic and none of the algorithms use machine learning (often referred to as “AI”), which tends to generate plausible looking fake details. The software used can be downloaded here.

The image processing steps were:

  1. Bias correction, dark current subtraction, flatfield correction, noise estimation
  2. Alignment and brightness calibration using stars from reference image
  3. Stacking with outlier rejection, background estimation and optimal weighting based on noise estimation
  4. Star subtraction where star positions and intensities are extracted from continuum images
  5. Denoising and deconvolution of both components (stars and residual)
  6. Dynamic range compression using non-linear high-pass filter
  7. Color composition and tonal curve correction

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