Other
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.0607s&link_type=abstract
American Astronomical Society, AAS Meeting #212, #6.07; Bulletin of the American Astronomical Society, Vol. 40, p.196
Other
Scientific paper
IRAS 17495-2534 is a highly obscured oxygen-rich AGB star that does not exhibit OH/IR maser emission. However, its IRAS LRS spectrum exhibits the strongest mid-infrared crystalline silicate absorption features seen to date. Consequently this source provides an unprecedented opportunity to test competing hypotheses for dust formation and to understand the formation of crystalline silicates.
This source is located in the Galactic plane at a distance of 4kpc, and thus may have higher than solar metallicity. However, comparing the spectrum to those of OH/IR stars in the Galactic Bulge shows that this source has significantly stronger crystalline silicate features, indicating that metallicity is not the only factor influencing crystal production.
Radiative transfer modeling of IRAS 17495-2534 suggests that both the crystalline and amorphous components of silicate dust are dominated by forsterite (Mg2SiO4) rather than enstatite (MgSiO3) or other more silica-rich compositions. We compare competing dust formation mechanisms and discuss whether they can explain this particular spectrum. Calculations predict that, in stars with relatively high mass-loss rates, the high pressure (leading to high dust formation temperatures) and slow outflow velocities (leading to slow cooling) should result in either direct formation of crystalline grains or rapid annealing and crystallization of initially amorphous silicates. However, spectra of most high mass-loss stars are interpreted to contain little crystalline material. We investigate the effects of C/O, metallicity, mass-loss rate and initial stellar mass on crystalline dust formation and discuss why there is apparently so little crystalline dust.
Speck Angela
Whittington Alan
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