The infrared spectral properties of magellanic carbon stars

Van Loon

Abstract

The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C2H2 at 7.5 µm. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in the DPR at lower metallicities, but it is not statistically significant. The most deeply embedded carbon stars have lower variability amplitudes and show SiC in absorption. In some cases they have bluer colors at shorter wavelengths, suggesting that the central star is becoming visible. These deeply embedded stars may be evolving off of the asymptotic giant branch and/or they may have non-spherical dust geometries.

Citation

Van Loon. (2016). The infrared spectral properties of magellanic carbon stars. Astrophysical Journal, https://doi.org/10.3847/0004-637X/826/1/44

• Acceptance Date: Apr 15, 2016
• Publication Date: Jul 18, 2016
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• DOI: https://doi.org/10.3847/0004-637X/826/1/44
• Keywords: circumstellar matter; infrared:stars; stars:AGB and post-AGB; stars:carbon
• Publisher URL: https://doi.org/10.3847/0004-637x/826/1/44