In Search of Possible Associations between Planetary Nebulae and Open Clusters

TL;DR

This paper investigates potential physical associations between planetary nebulae and open clusters, finding some promising cases especially where nebulae are in cluster coronae, but most are line of sight coincidences.

Contribution

It identifies and evaluates possible physical links between planetary nebulae and open clusters, highlighting cases warranting further study and noting the significance of cluster coronae.

Findings

7 of 13 nebulae are line of sight coincidences

6 cases where physical association is plausible

Strongest associations involve nebulae in cluster coronae

Abstract

We consider the possibility of cluster membership for 13 planetary nebulae that are located in close proximity to open clusters lying in their lines of sight. The short lifetimes and low sample size of intermediate-mass planetary nebulae with respect to nearby open clusters conspire to reduce the probability of observing a true association. Not surprisingly, line of sight coincidences almost certainly exist for 7 of the 13 cases considered. Additional studies are advocated, however, for 6 planetary nebula/open cluster coincidences in which a physical association is not excluded by the available evidence, namely M 1-80/Berkeley 57, NGC 2438/NGC 2437, NGC 2452/NGC 2453, VBRC 2 & NGC 2899/IC 2488, and HeFa 1/NGC 6067. A number of additional potential associations between planetary nebulae and open clusters is tabulated for reference purposes. It is noteworthy that the strongest cases involve planetary nebulae lying in cluster coronae, a feature also found for short-period cluster Cepheids, which are themselves potential progenitors of planetary nebulae.