Abstract
In order to determine the composition of the dust in the circumstellar envelopes of oxygen-rich asymptotic giant branch (AGB) stars, we have computed a grid of MODUST radiative-transfer models for a range of dust compositions, mass-loss rates, dust-shell inner radii and stellar parameters. We compare the resulting colours with the observed oxygen-rich AGB stars from the SAGE-Spec Large Magellanic Cloud (LMC) sample, finding good overall agreement for stars with a mid-infrared excess. We use these models to fit a sample of 37 O-rich AGB stars in the LMC with optically thin circumstellar envelopes, for which 5-35 μm Spitzer infrared spectrograph (IRS) spectra and broad-band photometry from the optical to the midinfrared are available. From the modelling, we find mass-loss rates in the range ̃8 × 10-8-5 × 10-6M⊙ yr-1, and we show that a grain mixture consisting primarily of amorphous silicates, with contributions from amorphous alumina and metallic iron, provides a good fit to the observed spectra. Furthermore, we show from dust models that the AKARI [11]-[15] versus [3.2]-[7] colour-colour diagram is able to determine the fractional abundance of alumina in O-rich AGB stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Original language | English |
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Pages (from-to) | 631-651 |
Number of pages | 20 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 440 |
Issue number | 1 |
DOIs | |
Publication status | Published - 2014 |
Keywords
- Circumstellar matter
- Dust, extinction
- Infrared: stars
- Magellanic clouds
- Radiative transfer
- Stars: AGB and post-AGB