The mass-loss rates and molecular abundances of S-type AGB stars

TL;DR

This study estimates mass-loss rates and molecular abundances in 40 S-type AGB stars, providing insights into their transitional nature and chemical evolution during stellar evolution.

Contribution

It offers the first comprehensive analysis of mass-loss and molecular composition in S-type AGB stars, bridging the gap between M-type and carbon stars.

Findings

Mass-loss rates are intermediate between M-type and carbon stars.

S-type stars show unique molecular abundance patterns.

Results support the evolutionary transition hypothesis.

Abstract

The S-type stars are believed to have a C/O-ratio close to unity (within a few percent). They are considered to represent an intermediate evolutionary stage as AGB stars evolve from oxygen-rich M-type stars into carbon stars. As possible transition objects the S-type stars could give important clues to the mass-loss mechanism(s) and to the chemical evolution along the AGB. Using observations of circumstellar radio line emission in combination with a detailed radiative transfer analysis, we have estimated mass-loss rates and abundances of chemically important molecules (SiO, HCN) for a sample of 40 S-type AGB stars. The results will be compared to previous results for M-type and carbon stars.