Carbon Stars

Carbon stars are typically cool giants with strong molecular bands of C2, CN, CH. The C2 Swan bands are the dominate optical spectral features. There is often a strong NaD line. The R series of C stars is hotter than the N series.

Some presumed giant C stars were seen to have high proper motions, and coupled with low luminosity, were determined to be the elusive dwarf carbon (dC) star.

Carbon features also make an appearance in the DQ class of white dwarfs, and carbon features are in common in the spectra of comets.

Some of my favorite carbon features include (in Angstroms): 3880 CN (STRONG in comets), 4056 C3 complex (STRONG in comets), 4217 CN, 4380 C2 Swan, 4738 C2 Swan, 5165 C2 Swan (STRONG), 5635 C2 Swan, 6122 C2 Swan

Note that the molecular carbon bands have a reverse profile than that of TiO, that is the carbon bands start with a sharp bandhead edge at the red end of the band and then taper off towards the blue.

N Series

N0 N2

N3 N4

N6 N7

R Series

R2 R3

R5 R6

R8

Misc

C8e C

C C