Fr.: nébuleuse de l'œuf pourri
A → bipolar nebula and → OH/IR source with technical designation OH 231.8+4.2. It is a → proto-planetary nebula (PPN) 1.4 → light-years long and located some 5,000 light-years from Earth in the constellation → Puppis. The obscured → central star, named QX Pup, is classified as M9-10 III and has a → Mira-like variability consistent with an evolved → asymptotic giant branch (AGB) star. The late evolution of this object may have been complex since it has a binary → companion star (of type A0 V) that has been indirectly identified from analysis of the spectrum of the hidden central source reflected by the nebular dust. The system has a total luminosity of ~ 104 Lsun and its systemic velocity relative to the → Local Standard of Rest is VLSR ~ 34 km s-1. OH 231.8+4.2 is very likely a member of the → open cluster M46 with a progenitor mass of ~ 3 Msun. The nebula is also known as the Rotten Egg Nebula because it contains a lot of sulphur, an element that, when combined with other elements, smells like a rotten egg (see, e.g., Prieto et al., 2015, A&A, 575, A84).
The name "Calabash Nebula" was first proposed by Icke & Preston, 1989, A&A, 211, 409. It refers to the apparent form of the object which resembles a calabash "a tree that has large, rounded gourdlike fruit; the fruit of any of these plants," from Sp. calabaza, possibly from Ar. qar'ah yâbisah "dry gourd," from Pers. kharabuz, used of various large melons; → nebula.