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We study a group of evolved M-stars in the Large Magellanic Cloud,characterized by a peculiar spectral energy distribution. While the $9.7~\mu$mfeature arises from silicate particles, the whole infrared data seem to suggestthe presence of an additional featureless dust species. We propose that thecircumstellar envelopes of these sources are characterized by a dual dustchemistry, with an internal region, harbouring carbonaceous particles, and anexternal zone, populated by silicate, iron and alumina dust grains. Based onthe comparison with results from stellar modelling that describe the dustformation process, we deduce that these stars descend from low-mass ($M <2~M_{\odot}$) objects, formed $1-4$ Gyr ago, currently evolving either in thepost-AGB phase or through an after-pulse phase, when the shell CNO nuclearactivity is temporarily extinguished. Possible observations able to confirm ordisregard the present hypothesis are discussed.

Do evolved stars in the LMC show dual dust chemistry?