Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.9304s&link_type=abstract
American Astronomical Society, AAS Meeting #211, #93.04; Bulletin of the American Astronomical Society, Vol. 39, p.889
Astronomy and Astrophysics
Astronomy
Scientific paper
When low to intermediate mass stars (0.8-8Msol) near the end of their lives, they enter the asymptotic giant branch (AGB) phase during which they return much of their mass to the interstellar medium (ISM). As gas drifts away from the star, it condenses into dust in shells around the star. As the star continues to age it throws this dust back into the ISM and a good understanding of what the AGB stars are returning to the ISM is essential to understanding how the ISM behaves. The spectra of these stars/dust shells can be divided in categories according to the shape and strength of the spectral features. The oxygen-rich AGB stars are divided into eight spectral classes based on how broad or narrow the silicate feature is; where SE1 has the broadest feature and SE8 the narrowest. This sequence is believed to represent a continuum of dust mineralogies from oxide-dominated (SE1) to olivine-glass-dominated (SE8) Using the radiative transfer code DUSTY, we determine the nature of the dust shells that give rise to these spectra in terms of size, density, composition, crystal structure, and the size/shape of the dust grains. We present the preliminary results of our study including our discovery of a previously unnoticed, narrow 9.7um feature that appears in all the classes. The dust grains cast into the ISM are the building blocks for new stars and planets and our understanding of this dust is crucial to our understanding of galactic chemical evolution.
Smith Anthony A.
Speck Angela Karen
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