NGC 1501
NGC 1501 is a planetary nebula with a complex structure, located in the northern constellation of Camelopardalis. It has the proper names Camel's Eye Nebula and the Oyster Nebula. The nebula was discovered on 27 August 1787 by the British-German astronomer William Herschel. The central star of NGC 1501 is located at a distance of approximately from the Sun, and is from the Galactic Center.
Properties
Designated CH Camelopardalis, the central star of this planetary nebula has a spectral type of , similar to that of a carbon-rich Wolf–Rayet star. It is a pulsating star, meaning that its brightness varies regularly and periodically. In the case of NGC 1501's progenitor star, this is incredibly fast, with the star's brightness changing significantly in just half an hour. An analysis of Gaia data suggests that the central star is a binary system.The overall shape of the nebula is close to a thin-shelled oblate spheroid, with a low to moderate ellipticity. The major axis spans an angular size of. There are a large lobes along the axes, with smaller bumps scattered across the surface. The three dimensional form has been described as a "boiling, tetra-lobed shell". Visible-light observations capture the glow of gases including hydrogen and nitrogen. Density peaks have a particle densities of up to 1,400 cm−3. The temperature of the free electrons in the nebula measured at up to, and the nebula turbulence is.
The total mass of the nebula is estimated to be around, most of which is ionized gas and a small fraction is carbon-rich dust. Expansion velocities range from. The estimated mass of the central star prior to entering the asymptotic giant branch stage and shedding its outer layer was.