SH2-185, also known as the γ Cas nebula or the Ghost of Cassiopeia, is a mixed emission/reflection nebula in the constellation Cassiopeia.
The nebula is ionized and illuminated by the star γ Cas and formed by its stellar wind.
With a spectral type of B0.5IVe ('e' denotes an emission line star), γ Cas exhibits unusually high X-Ray emission for its class.
The magnitude of the star varies slowly and is currently about 2.2.
The distance of the star and the nebula is approximately 550 light-years away according to Hipparcos.
The region also features some faint background nebulae, primarily visible in the infrared spectrum.
Click on the images for a full-scale/full-view version.
Both color composites suffer from artifacts caused by the bright star. In particular, these are:
H-alpha: Reflections between the image sensor and the filter. Due to the microlenses, the sensor surface acts like a reflective grating, resulting in periodic patterns of defocused stars as artifacts.
All colors: Halos caused by scattering in the atmosphere, possibly on very thin clouds of ice crystals. The effect is stronger for shorter wavelengths.
H-alpha: Internal filter reflections. This causes onion-like halos (rings whose brightness decreases step-wise with increasing radii).
All colors: A bias error caused by extreme sensor saturation in the pixel row of γ Cas. In the image, this results in a horizontal dark line going through the star.