SH2-290 (Abell 31)

SH2-290 (also known as Abell 31) is an old planetary nebula in the constellation Cancer with a low surface brightness. Its progenitor is the white dwarf WD 0851+090, located in a distance of about 1800 light-years (550 pc). At this distance, the apparent diameter of 0.33° corresponds to a true diameter of about 10 light-years (3.2 pc).

SH2-290 (Abell 31) in SHO
Click on the image to load it at full resolution in a JavaScript viewer.

In this false-color composite, [SII] is mapped to red, Hα to green, and [OIII] to blue. Stars are partially subtracted so that they appear white on average and to improve the visibility of the nebula. The progenitor, WD 0851+090, lies near the center of the nebula.

In the south (bottom), a shockwave can be seen that is likely caused by the motion of the planetary nebula relative to the surrounding interstellar medium (ISM). Furthermore, the nebula appears to be compressed in that direction, resulting in its oval shape. The orientation of the nebula and the shockwave corresponds with the direction of the proper motion of the progenitors (34 km/s to south-east) with a discrepancy of about 20°. That is an indication of motion of the ISM (relative to the Sun).

SH2-290 (Abell 31) in OHS
Compared to the image above, the mappings for red and blue are swapped, improving the visibility of [OIII]. Specifically, [OIII] is mapped to red, Hα to green, and [SII] to blue. As above, stars are partially subtracted.

Image data

FOV (full view in the JavaScript viewer): 0.58° × 0.47°°
Position (J2000): RA: 8h54m15s; DEC: 8°54′
Date: 2019-2025
Location: Pulsnitz, Germany
Instrument: 400mm Newton at f=1520mm
Camera Sensor: Panasonic MN34230
Orientation: North is up
Scale: 0.8 arcsec/pixel (at full resolution)
Total exposure times:
Hα (3 nm): 12.2 h
[OIII] (3 nm): 9.5 h
[SII] (3 nm): 18.5 h
Near infrared: 1.6 h
Blue: 1.1 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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