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.