The 21 micron and 30 micron circumstellar dust features in evolved C-rich objects

TL;DR

This paper reviews the 21 and 30 micron dust emission features in evolved carbon-rich stars, highlighting their occurrence, evolution, and the mystery surrounding their carriers across different stellar phases and galaxies.

Contribution

It provides a comprehensive overview of the occurrence and characteristics of these dust features in various stellar environments and discusses their potential related carriers.

Findings

21micron feature is rare and transient in PPNs

30micron feature is common across late stellar stages

Most 21micron sources also emit at 30micron

Abstract

The 21micron and 30micron bands are the strongest dust emission features detected in evolved low- and intermediate-mass C-rich stars (i.e. asymptotic giant branch [AGB] stars, proto-planetary nebulae [PPN], and planetary nebulae [PN]). While the 21micron feature is rare and exists only in the transient PPN phase, the 30micron feature is more common and seen in the entire late stage of stellar evolution, from AGB to PPN and PN phases, as well as in the low-metallicity galaxies: the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). The carriers of these features remain unidentified. Eleven of the twelve well-identified 21micron sources also emit in the 30micron band, suggesting that their carriers may be somewhat related.