Planetary nebula
Membership in clusters

Planetary nebulae have been detected as members in four Galactic globular clusters: Messier 15, Messier 22, NGC 6441 and Palomar 6. Evidence also points to the potential discovery of planetary nebulae in globular clusters in the galaxy M31. However, there is currently only one case of a planetary nebula discovered in an open cluster that is agreed upon by independent researchers. That case pertains to the planetary nebula PHR 1315-6555 and the open cluster Andrews-Lindsay 1. Indeed, through cluster membership, PHR 1315-6555 possesses among the most precise distances established for a planetary nebula (i.e., a 4% distance solution). The cases of NGC 2818 and NGC 2348 in Messier 46, exhibit mismatched velocities between the planetary nebulae and the clusters, which indicates they are line-of-sight coincidences. A subsample of tentative cases that may potentially be cluster/PN pairs includes Abell 8 and Bica 6, and He 2-86 and NGC 4463.

Theoretical models predict that planetary nebulae can form from main-sequence stars of between one and eight solar masses, which puts the progenitor star's age at greater than 40 million years. Although there are a few hundred known open clusters within that age range, a variety of reasons limit the chances of finding a planetary nebula within. For one reason, the planetary nebula phase for more massive stars is on the order of millennia, which is a blink of the eye in astronomic terms. Also, partly because of their small total mass, open clusters have relatively poor gravitational cohesion and tend to disperse after a relatively short time, typically from 100 to 600 million years.
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