Carbon-rich dust production in metal-poor galaxies in the Local Group

TL;DR

This study examines dust production in carbon stars across several metal-poor dwarf galaxies, revealing how metallicity influences dust composition and supporting theories on stellar evolution and dust contribution to the interstellar medium.

Contribution

It extends understanding of dust production in carbon stars to lower metallicities, showing how dust features vary with metallicity in dwarf spheroidal galaxies.

Findings

Dust presence varies among galaxies, less in Carina.

Weaker SiC emission correlates with lower metallicity.

Stronger acetylene absorption observed in more metal-poor stars.

Abstract

We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a star's lifetime on the asymptotic giant branch.