# 30-micron sources in galaxies with different metallicities

## TL;DR

This study analyzes the 30 micron dust feature in spectra of carbon-rich evolved stars across galaxies with different metallicities, revealing that metallicity influences the feature's formation, prominence, and wavelength shift.

## Contribution

It demonstrates that metallicity affects the formation and characteristics of the 30 micron dust feature in carbon-rich stellar objects, using the Manchester method for analysis.

## Key findings

- The 30 micron feature appears at lower mass-loss rates in metal-rich environments.
- The feature is more prominent in Galactic carbon stars compared to metal-poor ones.
- In planetary nebulae, the feature shifts to longer wavelengths with decreasing metallicity.

## Abstract

We present an analysis and comparison of the 30 micron dust features seen in the Spitzer Space Telescope spectra of 207 carbon-rich asymptotic giant branch (AGB) stars, post-AGB objects, and planetary nebulae located in the Milky Way, the Magellanic Clouds (MCs), or the Sagittarius dwarf spheroidal galaxy (Sgr dSph), which are characterised by different average metallicities. We investigated whether the formation of the 30 micron feature carrier may be a function of the metallicity. Through this study we expect to better understand the late stages of stellar evolution of carbon-rich stars in these galaxies. Our analysis uses the `Manchester method' as a basis for estimating the temperature of dust for the carbon-rich AGB stars and the planetary nebulae in our sample. We used a black-body function with a single temperature deduced from the Manchester method or its modification to approximate the continuum under the 30 micron feature. The most important conclusion of our work is the fact that the formation of the 30 micron feature is affected by metallicity. Specifically that, as opposed to more metal-poor samples of AGB stars in the MCs, the feature is seen at lower mass-loss rates, higher temperatures, and has seen to be more prominent in Galactic carbon stars. The averaged feature (profile) in the AGB, post-AGB objects, and PNe seems unaffected by metallicity at least between a fifth and solar metallicity, but in the case of PNe it is shifted to significantly longer wavelengths.