The chemical composition and evolutionary state of the early stars

Abstract

Using moderate to high-resolution data from the visible, near-infrared, and infrared, abundance analyses have been performed on a sample of 11 R0-R5 stars in order to determine the general metallicity (Fe and Ti), any enhancement of s-process elements, the isotopic ratio C-12/C-13, and the abundances of C, N, and O. The iron abundance of 10 stars is nearly solar, and the s-process elements have no demonstrable enhancement in the sample. A 0.7 dex enhancement of carbon relative to the G-K giants is found in eight stars, while nitrogen is enhanced by a small amount. Oxygen has nearly the value found in the sun, while the C-12/C-13 ratio indicates an enrichment of C-13 with respect to the majority of faint stars. A discussion of the evolutionary state of the class of early R stars based on these results is presented.