Computer Science
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40848c&link_type=abstract
Spitzer Proposal ID #40848
Computer Science
Scientific paper
Mid-IR spectroscopic observations of O-rich AGB stars generally show the presence of copious amounts of circumstellar dust, often characterized by strong emission or absorption due to amorphous silicates. Detectable fractions of crystalline silicates have so far only be found in stars with high mass loss rates. Here we propose to spectroscopically observe -- using Spitzer-IRS from 9.9 -- 37.2 micron at high-resolution -- a homogeneous sample of 13 O-rich AGB stars spanning a large range in mass loss rates, and which all show tantalizing evidence for the presence of crystalline silicates in their low resolution spectra. The target stars are selected from a sample of O-rich AGB stars in the Galactic Bulge that was observed with IRS at low resolution with the aim to study the variations in the dust composition as a 1.5 solar mass star evolves along the AGB. The proposed observations will allow us to i) unambiguously confirm the presence of crystalline silicates in AGB stars with low- to intermediate mass loss rates; ii) determine at what phase in the AGB crystalline silicates are first formed and hence where they fit in the dust condensation sequence for O-rich AGB stars iii) determine the temperature and chemical composition of these crystalline silicates and hence iv) understand how these crystalline silicates are formed and how they evolve as they sail away from the central star; and finally v) what stellar parameters are important for the efficient formation of crystalline silicates.
Blommaert Joris
Cami Jan
Justtanont Kay
Kemper Ciska
Tielens Alexander
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