Context. H II regions and planetary nebulae (PNe) both emit at radio and infrared (IR) wavelengths, and angularly small H II regions can be mistaken for PNe. This problem of classification is most severe for H II regions in an early evolutionary stage, those that are extremely distant, or those that are both young and distant. Previous work has shown that H II regions and PNe can be separated based on their infrared colors.
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Anderson et al. (2011) studied this question.
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