Modelling the alumina abundance of oxygen-rich evolved stars in the large magellanic cloud

O. C. Jones, F. Kemper, S. Srinivasa, I. McDonald, G. C. Sloa, A. A. Zijlstra

    Research output: Contribution to journalArticlepeer-review

    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 languageEnglish
    Pages (from-to)631-651
    Number of pages20
    JournalMonthly Notices of the Royal Astronomical Society
    Volume440
    Issue number1
    DOIs
    Publication statusPublished - 2014

    Keywords

    • Circumstellar matter
    • Dust, extinction
    • Infrared: stars
    • Magellanic clouds
    • Radiative transfer
    • Stars: AGB and post-AGB

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