Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21725016m&link_type=abstract
American Astronomical Society, AAS Meeting #217, #250.16; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astrophysics
Scientific paper
Cosmic dust plays an important role in many astrophysical environments. A major source of cosmic dust is dying stars. Intermediate mass stars (0.8-8 solar masses) eventually evolve to become Asymptotic Giant Branch (AGB) stars which produce vast quantities of dust. During the AGB phase, the star expands and contracts releasing shells of gas that drift away from the star and eventually cool to condense dust. Using spectral observations from the Infrared Space Observatory (ISO), we have investigated the far-infrared spectral dust features (in the 15-40 micron range) from a large sample of AGB star spectra. Previously, it has been thought that these circumstellar dust shells are dominated by amorphous (glassy) silicates and that crystalline grains are rare. Furthermore, on those rare occasions that crystalline silicates occur, they are expected (and usually observed) to be Mg-rich. Using laboratory spectra of crystalline olivines and pyroxenes with a range of Mg/Fe, we show that the majority of the observed astronomical spectra are matched surprisingly well with crystalline silicates, especially with high iron content. This discovery contradicts the previously accepted dust composition. Fe-rich crystalline silicate dust compositions are inconsistent with current dust formation hypothesis and dust condensation sequences, and thus our research calls the current accepted wisdom into question.
Guha Niyogi Suklima
Miller Lucas
Speck Angela
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