Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.0603s&link_type=abstract
American Astronomical Society, AAS Meeting #212, #6.03; Bulletin of the American Astronomical Society, Vol. 40, p.195
Astronomy and Astrophysics
Astronomy
Scientific paper
Stars with main-sequence masses in the range 0.8-8M_sol eventually evolve to become asymptotic giant branch (AGB) stars during which they eject much of their mass and form circumstellar shells of dust and gas. During the AGB phase, these stars evolve both in terms of the strength of their mass-loss and chemically, although there are competing hypotheses for how these evolutionary changes manifest themselves in terms of dust production. These hypotheses fall into two basic categories: (1) mass-loss rate determine mineralogy; and (2) C/O determine mineralogy. The spectra of optically thin O-rich AGB stars/dust shells have been divided into Silicate Emission Indices (SE#) according to the relative strengths of the spectral features at 10, 11 and 12um, such that 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 silicate-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 size of the dust grains. Taking into account the inherent degeneracies in such modeling, we determine the trends in dust shell parameters that are associated with the shift from broad to narrow 10um feature and interpret this in terms of the expected physical and chemical evolution of these systems.
Smith Anthony A.
Speck Angela Karen
Wheeler Caleb H.
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