Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.7904s&link_type=abstract
American Astronomical Society, AAS Meeting #211, #79.04; Bulletin of the American Astronomical Society, Vol. 39, p.870
Other
Scientific paper
We have conducted an infrared spectroscopic survey with the Spitzer Space Telescope of evolved stars in the Magellanic Clouds and compared our results to previous studies of evolved stars in the Galaxy. As the metallicity of the host galaxy decreases, the fraction of naked stars increases. Among the oxygen-rich naked stars, absorption from SiO, the precursor to silicate grains, decreases with metallicity. The lack of SiO in the naked stars raises the question of how the silicates form in the dusty stars. Stars with shorter pulsation periods show less dust than their Galactic counterparts, while stars with longer periods (> 700 days) show similar quantities of dust. Silicates dominate the oxygen-rich dust shells in the Magellanic sample, while Galactic dust shells often include amorphous alumina. Our sample includes three deeply embedded stars showing crystalline silicate emission features at longer wavelengths and two long-period Mira variables with crystalline silicate emission at 10 um. The crystalline grains are magnesium-rich, as in the Galaxy. Several oxygen-rich spectra show an emission feature at 14 um, which we verify as a newly recognized dust feature. The carbon-rich sample confirms previous results from other surveys showing that as carbon stars become more metal-poor, the ratio of SiC dust and MgS dust to amorphous carbon decreases, while the column density of acetylene gas rises. Carbon stars with similar pulsation properties in the Galaxy, LMC, and SMC have similar dust mass-loss rates, despite their differences in initial metallicity.
Bernard-Salas Jeronimo
Devost Daniel
Houck James R.
Kraemer Kathleen E.
Sargent Ben
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