The carbon star mystery: why do the low mass ones become such, and where have all the high mass ones gone?
Most C stars achieve their carbon-rich characteristics while in the asymptotic giant branch (AGB) phase of evolution. Theoretical calculations by Iben (1974, 1975, 1976) have shown that a 'dredge-up' process can bring to the surface of an AGB star some of the fresh carbon that is formed in the helium- and carbon-rich convective shell during a thermal pulse, and that this process will ultimately lead to the development of C star characteristics. The investigation demonstrates that, if the observations are to be understood, significant dredge-up must occur in thermally pulsing ABG stars of low metal abundances when core mass is considerably smaller than 0.6 solar masses. The discussion which focuses on the properties of a homogeneous and complete sample of C stars whose distances are well known, is complementary to a recent study by Scalo and Miller (1979), which focuses on the properties of C stars in the Galaxy.