The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
Published July 25, 2016 | Version v1
Conference paper Open

Constraining dust properties in Circumstellar Envelopes of C-stars in the Small Magellanic Cloud: optical constants and grain size of carbon dust

Authors/Creators

  • 1. Università di Padova, Italy
  • 2. Royal Observatory of Belgium, Brussel, Belgium
  • 3. Osservatorio Astronomico di Padova, Italy
  • 4. SISSA, Trieste, Italy

Contributors

  • 1. Uppasala University

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. 
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.
In particular, the different choices of optical properties and grain size lead to differences
in the NIR and MIR colors greater than two magnitudes in some cases. 


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
TP-AGB phase through resolved stellar populations in the framework of the STARKEY project.

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Additional details

Funding

European Commission
STARKEY - Solving the TP-AGB STAR Conundrum: a KEY to Galaxy Evolution 615604

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