Modelling the alumina abundance of oxygen-rich evolved stars in the Large Magellanic Cloud. Issue 1 (12th March 2014)

• Record Type: Journal Article
• Authors: Jones, O. C.; Kemper, F.; Srinivasan, S.; McDonald, I.; Sloan, G. C.; Zijlstra, A. A.
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 440:Issue 1(2014)
• Page Start: 631
• Page End: 651
• Publication Date: 2014-03-12
• Subjects: radiative transfer -- stars: AGB and post-AGB -- circumstellar matter -- dust, extinction -- Magellanic Clouds -- infrared: stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stu286
• Languages: English
• ISSNs: 0035-8711

Abstract

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 mid-infrared are available. From the modelling, we find mass-loss rates in the range ∼8 × 10 −8 –5 × 10 −6 M⊙ 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.