Constraining Dust Properties In Circumstellar Envelopes Of C-Stars In The Small Magellanic Cloud: Optical Constants And Grain Size Of Carbon Dust
Creators: name: Nanni, Ambra
Publisher: name: Zenodo
Year: 2016
Subjects: TP-AGB
carbon dust
Magellanic Clouds
Near and Mid Infrared observations

description: We present our recent investigation aimed at constraining the typical size and optical properties of carbon dust grains in Circumstellar envelopes (CSEs) of carbon-rich stars (C-stars) in the Small Magellanic Cloud (SMC).

We applied our recent dust growth model, coupled with a radiative transfer code, to the dusty CSEs of C-stars along the TP-AGB phase, for which we computed spectra and colors. We then compared our modeled colors in the Near and Mid Infrared (NIR and MIR) bands with the observed ones, testing different assumptions in our dust scheme and employing different optical constants data sets for carbon dust. <br>
We constrained the optical properties of carbon dust by identifying the combinations of typical grain size and optical constants data set which simultaneously reproduce several colors in the NIR and MIR wavelengths.<br>
In particular, the different choices of optical properties and grain size lead to differences<br>
in the NIR and MIR colors greater than two magnitudes in some cases. 

<br>
We concluded that the complete set of selected NIR and MIR colors are best reproduced by small grains, with sizes between 0.06 and 0.1 $\mu$m, rather than by large grains of 0.2-0.4 $\mu$m. The inability of large grains to reproduce NIR and MIR colors is found to be independent of the adopted optical data set and the deviations between models and observations tend to increase for increasing grain sizes. We also find a possible trend of the typical grain size with mss-loss and/or carbon-excess in the CSEs of these stars.

The work presented is preparatory to future studies aimed at calibrating the<br>
TP-AGB phase through resolved stellar populations in the framework of the STARKEY project.
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