Composition of field halo stars and the chemical evolution of the halo

On the basis of an evaluation of observational data and the theory of stellar evolution, a number of rather simple scenarios have been constructed for the interpretation of many puzzling features in the Galaxy. The present paper is concerned with aspects of chemical evolution in the case of the field stars of the halo, taking into account a study of the variation of the abundances of the elements as a function of iron abundance. Since iron abundance is statistically correlated with the age of a star, this approach makes it possible to obtain a relation between element abundances and the age of the observed stars. The very light elements, including helium, deuterium, lithium, beryllium, and boron, are considered along with the light elements carbon, nitrogen, oxygen, and sulfur. The analysis of the CNO elements in halo dwarfs shows that oxygen is less deficient than carbon or iron. 64 references