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In order to determine the composition of the dust in the circumstellarenvelopes of oxygen-rich asymptotic giant branch (AGB) stars we have computed agrid of modust radiative-transfer models for a range of dust compositions,mass-loss rates, dust shell inner radii and stellar parameters. We compare theresulting colours with the observed oxygen-rich AGB stars from the SAGE-SpecLarge Magellanic Cloud (LMC) sample, finding good overall agreement for starswith a mid-infrared excess. We use these models to fit a sample of 37 O-richAGB stars in the LMC with optically thin circumstellar envelopes, for which5$-$35-$\mu$m Spitzer infrared spectrograph (IRS) spectra and broadbandphotometry from the optical to the mid-infrared are available. From themodelling, we find mass-loss rates in the range $\sim 8\times10^{-8}$ to$5\times10^{-6}$ M$_{\odot}\ \mathrm{yr}^{-1}$, and we show that a grainmixture consisting primarily of amorphous silicates, with contributions fromamorphous alumina and metallic iron provides a good fit to the observedspectra. Furthermore, we show from dust models that the AKARI [11]$-$[15]versus [3.2]$-$[7] colour-colour diagram, is able to determine the fractionalabundance of alumina in O-rich AGB stars.

Modelling the alumina abundance of oxygen-rich evolved stars in the Large Magellanic Cloud