The origin of extremely metal-poor carbon stars and the search for population III

The number of known extremely metal-deficient stars has recently increased substantially, stimulating inquiry into the formation and initial chemical evolution of the Milky Way. In order to draw proper inferences from the observations, it is necessary to understand the evolution of these low-mass stars and the modifications in their surface elemental abundances that they have experienced during their long lifetimes. Among the observations to be explained is the fact that the incidence of carbon-enhanced stars increases with decreasing metallicity. We show that low-mass, extremely metal-poor stars evolve into carbon stars along paths that are quite different from those followed by more metal-rich stars of younger populations. This permits us, in principle, to distinguish the brightest survivors of the first generations of stars formed in the universe (Population III carbon stars) from stars belonging to younger populations.