Carbon stars in the X-shooter Spectral Library
  We provide a new collection of spectra of 35 carbon stars obtained with the
ESO/VLT X-shooter instrument as part of the X-shooter Spectral Library project.
The spectra extend from 0.3$\mu$m to 2.4$\mu$m with a resolving power above
$\sim$ 8000. The sample contains stars with a broad range of (J-K) color and
pulsation properties located in the Milky Way and the Magellanic Clouds. We
show that the distribution of spectral properties of carbon stars at a given
(J-K) color becomes bimodal (in our sample) when (J-K) is larger than about
1.5. We describe the two families of spectra that emerge, characterized by the
presence or absence of the absorption feature at 1.53$\mu$m, generally
associated with HCN and C$_2$H$_2$. This feature appears essentially only in
large-amplitude variables, though not in all observations. Associated spectral
signatures that we interpret as the result of veiling by circumstellar matter,
indicate that the 1.53$\mu$m feature might point to episodes of dust production
in carbon-rich Miras.
