Determining the forsterite abundance of the dust around AGB stars

TL;DR

This paper introduces a diagnostic tool to measure forsterite dust abundance around AGB stars using spectral band analysis, revealing higher abundances than previously known.

Contribution

A new method based on spectral band comparison to accurately determine forsterite abundance in AGB star dust shells.

Findings

Forsterite abundance can reach 12% by mass in AGB stars.

The 11.3 μm band is a reliable indicator of forsterite abundance.

Previous maximum forsterite abundance was 5%, now found to be higher.

Abstract

We present a diagnostic tool to determine the forsterite abundance of the dust ejected by AGB stars. Our method is based on a comparison between the observed strength of spectral bands of forsterite and model calculations. We show that the 11.3 {\mu}m forsterite band is a robust indicator of the forsterite abundance of the current mass-loss period for AGB stars with an optically thick dust shell. The 33.6 {\mu}m band of forsterite is sensitive to changes in the density and the geometry of the emitting dust shell, and so a less robust indicator. We apply this method to six high mass-loss rate AGB stars, showing that AGB stars can have forsterite abundances of 12% by mass and higher, which is more than the previously found maximum abundance of 5%.