Carbon stars from LAMOST DR2 data

In this work, we present the new catalog of carbon stars from the LAMOST DR2 catalog. In total, 894 carbon stars are identified from multiple line indices measured from the stellar spectra. Combining the CN bands in the red end with \ctwo\ and other lines, we are able to identify the carbon stars. Moreover, we also classify the carbon stars into spectral sub-types of \ch, \CR, and \cn. These sub-types approximately show distinct features in the multi-dimensional line indices, implying that in the future we can use them to identify carbon stars from larger spectroscopic datasets. Meanwhile, from the line indices space, while the \cn\ stars are clearly separated from the others, we find no clear separation between \CR\ and \ch\ sub-types. The \CR\ and \ch\ stars seem to smoothly transition from one to another. This may hint that the \CR\ and \ch\ stars may not be different in their origins but look different in their spectra because of different metallicity. Due to the relatively low spectral resolution and lower signal-to-noise ratio, the ratio of $^{12}$C/$^{13}$C is not measured and thus the \cj\ stars are not identified.