
NGC 2438

NGC 2438 is a planetary nebula in the southern constellation of Puppis. Parallax measurements by Gaia put the central star at a distance of roughly 1,370 light years. It was discovered by William Herschel on March 19, 1786. NGC 2438 appears to lie within the cluster M46, but it is most likely unrelated since it does not share the cluster's radial velocity. The case is yet another example of a superposed pair, joining the famed case of NGC 2818.
This is a multi-shell planetary nebula with a bright inner nebula with a diameter of , consisting of two somewhat detached shells. It is expanding with a velocity of . The structure is surrounded by a fainter, mostly circular halo that is more visible on the western half, and has a diameter of . The mass of the main nebula is estimated at , while the shell has 0.5–. The main nebula has a temperature of about 10–13,000 K, rising to 15–17,000 K at the inner edge.
The nebula consists of material ejected from the central star during the asymptotic giant branch stage, beginning some 8,500 years ago. The main nebula was formed at about half that age. The central star of this planetary nebula is a 17.7-magnitude white dwarf, with surface temperature of about . It is one of the hottest stars known.