Molecular processes from the AGB to the PN stage

TL;DR

This review discusses molecular processes during the transition from AGB stars to planetary nebulae, highlighting the detection of complex molecules like fullerenes and graphene, and emphasizing astrochemical formation pathways.

Contribution

It provides an observational overview of molecular processes in late stellar evolution, focusing on the first detections of fullerenes and graphene in planetary nebulae.

Findings

Detection of fullerenes and graphene in planetary nebulae

Constraints on gas-phase and solid-state chemistry models

Insights into formation pathways of complex molecules in space

Abstract

Many complex organic molecules and inorganic solid-state compounds have been observed in the circumstellar shell of stars (both C-rich and O-rich) in the transition phase between Asymptotic Giant Branch (AGB) stars and Planetary Nebulae (PNe). This short (~100-10.000 years) phase of stellar evolution represents a wonderful laboratory for astrochemistry and provides severe constraints on any model of gas-phase and solid-state chemistry. One of the major challenges of present day astrophysics and astrochemistry is to understand the formation pathways of these complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene in the case of a C-rich chemistry and oxides and crystalline silicates in O-rich environments) in space. In this review, I present an observational review of the molecular processes in the late stages of stellar evolution with a special emphasis on the first detections of fullerenes and graphene in PNe.