Molecular studies of Planetary Nebulae

TL;DR

This paper reviews recent molecular observations in planetary nebulae, highlighting their complex chemistry, formation of fullerenes, and contribution to interstellar medium enrichment, advancing understanding of stellar evolution and astrochemistry.

Contribution

It provides a summary of recent molecular detections in planetary nebulae and discusses their implications for circumstellar chemistry and interstellar medium enrichment.

Findings

Over 20 molecular species identified in PNe.

Fullerenes and complex organics can form and survive during PNe evolution.

PNe contribute significantly to ISM molecular enrichment.

Abstract

Circumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN progenitors have been heavily processed by strong ultraviolet radiation from the central star. Intriguingly, fullerenes and complex organic compounds having aromatic and aliphatic structures can be rapidly formed and largely survive during the PPN/PN evolution. The similar molecular compositions in PNe and diffuse clouds as well as the detection of C$_{60}^+$ in the ISM reinforce the view that the mass-loss from PNe can significantly enrich the ISM with molecular species, some of which may be responsible for the diffuse interstellar bands. In this contribution, I briefly summarize some recent observations of molecules in PNe, with emphasis on their implications on circumstellar chemistry.