Carbon star

Carbon stars have quite distinctive spectral characteristics,[2] and they were first recognized by their spectra by Angelo Secchi in the 1860s, a pioneering time in astronomical spectroscopy.

In addition to carbon, S-process elements such as barium, technetium, and zirconium are formed in the shell flashes and are "dredged up" to the surface.

Later correlation of this R to N scheme with conventional spectra, showed that the R-N sequence approximately run in parallel with c:a G7 to M10 with regards to star temperature.

[11] In the classical carbon stars, those belonging to the modern spectral types C-R and C-N, the abundance of carbon is thought to be a product of helium fusion, specifically the triple-alpha process within a star, which giants reach near the end of their lives in the asymptotic giant branch (AGB).

Since the luminosity rises, the star expands so that the helium fusion ceases, and the hydrogen shell burning restarts.

The enigmatic hydrogen deficient carbon stars (HdC), belonging to the spectral class C-Hd, seems to have some relation to R Coronae Borealis variables (RCB), but are not variable themselves and lack a certain infrared radiation typical for RCB:s. Only five HdC:s are known, and none is known to be binary,[12] so the relation to the non-classical carbon stars is not known.

Owing to its low surface gravity, as much as half (or more) of the total mass of a carbon star may be lost by way of powerful stellar winds.

[13] This dust is believed to be a significant factor in providing the raw materials for the creation of subsequent generations of stars and their planetary systems.

The material surrounding a carbon star may blanket it to the extent that the dust absorbs all visible light.

Silicon carbide outflow from carbon stars was accreted in the early solar nebula and survived in the matrices of relatively unaltered chondritic meteorites.

Stellar outflow from carbon stars is the source of the majority of presolar silicon carbide found in meteorites.