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Published online by Cambridge University Press: 04 August 2017
The Ba II, CH, and R0-R3 carbon stars are related in that they are giant stars having about the same position in the HR diagram, and having enhancements of carbon features. The Ba II and CH stars are also noted for enhancements of s process elements. The Ba II stars normally don't exhibit C2 bands that are characteristic of the CH and R stars, indicating that the Ba II stars have a C/O ratio close to but less than unity (Smith 1983). The Ba II and R stars are members of the old disk population (e.g. Eggen 1972), whereas the CH stars are high velocity, population II stars (Keenan 1942).