The Abundance of SiC$_2$ in Carbon Star Envelopes

TL;DR

This study investigates the prevalence and abundance of SiC$_2$, SiC, and Si$_2$C molecules in the envelopes of carbon-rich AGB stars to understand their potential role as precursors to silicon carbide dust formation.

Contribution

It provides the first comprehensive analysis of the distribution and abundance of SiC$_2$, SiC, and Si$_2$C in C-rich AGB star envelopes, highlighting SiC$_2$'s abundance.

Findings

SiC$_2$ is highly abundant in C-rich AGB star envelopes.

The presence of SiC and Si$_2$C is confirmed in certain stars.

SiC$_2$ is a likely gas-phase precursor to SiC dust formation.

Abstract

Silicon carbide dust grains are ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. To date, only three molecules containing an Si--C bond have been identified to have significant abundances in C-rich AGB stars: SiC$_2$, SiC, and Si$_2$C. The ring molecule SiC$_2$ has been observed in a handful of evolved stars, while SiC and Si$_2$C have only been detected in the C-star envelope IRC +10216. We aim to study how widespread and abundant SiC$_2$, SiC, and Si$_2$C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars.