The evolved-star dust budget of the Small Magellanic Cloud: the critical   role of a few key players
  The lifecycle of dust in the interstellar medium (ISM) is heavily influenced by outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars, a large fraction of which is contributed by a few very dusty sources. We compute the dust input to the Small Magellanic Cloud (SMC) by fitting the multi-epoch mid-infrared spectral energy distributions (SEDs) of AGB/RSG candidates with models from the {\em G}rid of {\em R}SG and {\em A}GB {\em M}odel{\em S} (GRAMS) grid, allowing us to estimate the luminosities and dust-production rates (DPRs) of the entire population. By removing contaminants, we guarantee a high-quality dataset with reliable DPRs and a complete inventory of the dustiest sources. We find a global AGB/RSG dust-injection rate of $(1.3\pm 0.1)\times 10^{-6}$ \msunperyr, in agreement with estimates derived from mid-infrared colours and excess fluxes. As in the LMC, a majority (66\%) of the dust arises from the extreme AGB stars, which comprise only $\approx$7\% of our sample. A handful of far-infrared sources, whose 24 \mic\ fluxes exceed their 8 \mic\ fluxes, dominate the dust input. Their inclusion boosts the global DPR by $\approx$1.5$\times$, making it necessary to determine whether they are AGB stars. Model assumptions, rather than missing data, are the major sources of uncertainty; depending on the choice of dust shell expansion speed and dust optical constants, the global DPR can be up to $\approx$10 times higher. Our results suggest a non-stellar origin for the SMC dust, barring as yet undiscovered evolved stars with very high DPRs. 
Sundar Srinivasan, Martha L. Boyer, Francisca Kemper, Margaret   Meixner, David Riebel, Benjamin A. Sargent
astro-ph.SR astro-ph.GA