Understanding the evolution and dust formation of carbon stars in the
  LMC with a look at the JWST
  Carbon stars have been and are extensively studied, given their complex
internal structure and their peculiar chemical composition, which make them
living laboratories to test stellar structure and evolution theories of evolved
stars. They are the most relevant dust manufacturers, thus playing a crucial
role in the evolution of galaxies. We study the dust mineralogy of
circumstellar envelope (CE) of C-stars in the Large Magellanic Cloud (LMC), to
achieve a better understanding of the dust formation process in the outflow of
these objects. We investigate the expected distribution of C-stars in the
observational planes built with the MIRI filters mounted onboard the James Webb
Space Telescope (JWST), to select the best planes allowing an exhaustive
characterisation of the stars. We compare the synthetic spectral energy
distributions, obtained by the modelling of asymptotic giant branch stars and
of the dust formation process in the wind, with the spectra of carbon stars in
the LMC, taken with the Infrared Spectrograph (IRS) onboard the Spitzer Space
Telescope. From the detailed comparison between synthetic modelling and
observation we characterise the individual sources and derive the detailed
mineralogy of the dust in the CE. We find that precipitation of MgS on SiC
seeds is common to all non metal-poor carbon stars. Solid carbon is the
dominant dust component, with percentages above $80\%$ in all cases; a
percentage between $10\%$ and $20\%$ of carbon dust is under the form of
graphite, the remaining being amorphous carbon. Regarding the observational
planes based on the MIRI filters, the colour-magnitude ([F770W]-[F1800W],
[F1800W]) plane allows the best understanding of the degree of obscuration of
the stars, while the ([F1800W]-[F2550W], [F1800W]) diagram allows a better
discrimination among stars of different metallicity.
