Here's a (mostly uncalibrated) spectrum of the best-known carbon star, Mu Cephei, from our campus observatory. It covers roughly the same wavelength span as the SDSS spectra do. The distinguishing features are the very broad absorption dips, broadened because molecules produce rich sets of absorption lines blending into bands instead of individual narrow absorption lines as single atoms do. (The major shortfall of calibration here is that the star is really considerably redder than this plot suggests). These absorptions, which are concentrated in the bluer part of the spectrum for the relevant carbon compounds, accentuate the red color due to low temperature and make carbon stars the most vividly hued of stars. Mu Cephei itself, Herschel's "Garnet Star", is a real showpiece at the telescope for public evenings.
