As spectroscopic samples of extragalactic globular clusters have grown, so
have the number of known [O III]-emitting sources in globular clusters.
Some of these sources are planetary nebulae (PNe), and can help constrain
theories of the binary origin of PNe. However, others can not be explained
as PNe, and may be due to supernova remnants, intermediate-mass black
holes, or other exotic phenomena. We review the natures of the known
[O III] sources in globular clusters, and propose a plan to search for these
objects more systematically in the future.
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