NGC 1501 is aplanetary nebula with a complex structure, located in the northernconstellation ofCamelopardalis. It has the proper namesCamel's Eye Nebula and theOyster Nebula.[3] The nebula was discovered on 27 August 1787 by the British-German astronomerWilliam Herschel.[5][6] The central star of NGC 1501 is located at a distance of approximately 3,840light-years (1.177 kpc) from theSun, and is 29,280 light-years (8.978 kpc) from theGalactic Center.[2]
ATESSlight curve for CH Camelopardalis, adapted from Córsicoet al., (2021)[7]
DesignatedCH Camelopardalis,[8] the central star of this planetary nebula has aspectral type of [WC4], similar to that of acarbon-richWolf–Rayet star.[9] It is a pulsating star, meaning that its brightness varies regularly and periodically.[8] 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 ofGaia data suggests that the central star is abinary system.[10]
The overall shape of the nebula is close to a thin-shelledoblate spheroid, with a low to moderateellipticity. Themajor axis spans an angular size of44″.[11] 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".[12] Visible-light observations capture the glow of gases including hydrogen and nitrogen.[13] 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 to11,500 K, and the nebula turbulence is18 km/s.[12]
The total mass of the nebula is estimated to be around 0.22 M☉, most of which is ionized gas (0.21 M☉) and a small fraction (8.9×10−4M☉) is carbon-rich dust.[14] Expansion velocities range from38 to 55 km/s.[12] The estimated mass of the central star prior to entering theasymptotic giant branch stage and shedding its outer layer was0.80–0.88 M☉.[14]
^abMosher, T.; et al. (December 2023). "Investigation of the Variable Star CH Camelopardalis in the Planetary Nebula NGC 1501".The Journal of the American Association of Variable Star Observers.51 (2): 159.Bibcode:2023JAVSO..51..159M.
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