SH2-184 (NGC 281, Pacman Nebula) is an emission nebula in constellation Cassiopeia with an apparent diameter of about 40' (arcminutes).
The nebula is mainly ionized by the young (only about 3.5 million years old, ) star cluster IC 1590, in particular by the multiple star system HD 5005.
Distance of HD 5005 according to Gaia DR3 data is about 10,000 (±650) light years (ly).
The nebula contains many Bok globules. This are dust concentrations undergoing an gravitational collapse which results in new stars.
A larger star formation region is NGC 281-W (or NGC 281 West). For this region there exist radio parallax measurements for an H2O maser (): about 9200 (±850) ly and Methanol masers (): about 7800 (±450) ly
Click on the images for a full scale version.
0.67° × 0.5°
400mm Newton at f=1520mm
North is up (approximately)
0.8 arcsec/pixel (at full resolution)
Total exposure times:
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:
Bias correction, photon counting
Dark current subtraction, flatfield correction, noise estimation
Alignment and brightness calibration using stars from reference image
Stacking with masking unlikely values and background correction
Extracting stars from the emission line images using information from continuum images
Denoising and deconvolution both components (stars and residual)
Dynamic range compression using non-linear high-pass filter