About this object
Planetary nebula NGC 40 is a low-excitation nebula in the constellation of Cephus, about 3500 light years away from Earth. The central star is fairly bright (about magnitude 11.6), has a mass of around 0.7 solar masses, and is much hotter than would be expected just from the properties of the surrounding nebula. This is because its temperature of around 90000 degrees should be hot enough to excite the nebula to a much higher ionization state than is found. This suggests the presence of shielding material between the star and the glowing nebula. Such higher density material could form in the shock interface between the fast wind (about 1800 km/s) from the central star and the nebular shells themselves. The nebular material covers about 25% of the sky as viewed by the central star, implying rather asymmetric mass-loss from the star in its asymptotic giant branch stage. NGC 40 has an extended halo, not seen here, probably caused by earlier mass ejection.
Location: 00 13.0 +72 32 (2000), size: about one light year across.