Abundances in K Giant Stars. I. a Determination of the Abundances in the Hyades K Giants.

Abstract

Differential curve-of-growth abundance analyses for the Hyades K giants, , , and E Tauri are presented, the Sun being used as the reference star. The conventional type of analysis results in a consistent model with abundances that do not agree with abundances previously found applicable to the Hyades G dwarfs. The requirement that the K giants should have the same abundances as the G dwarfs forces a modification of the reduction procedure. Treatment of the neutral and the ionized lines separately, corresponding effectively to adoption of a two-level atmosphere, permits successful recovery of the Hyades G dwarf abundances. The derived atmospheric parameters appear reasonable. The increase of complexity in the analysis apparently results from the difficulty of assigning levels in the solar atmosphere to line formation. The only abundance anomalies found are: (1) in Tauri, Zr is definitely deficient by a factor of 2, relative to Fe, and V, Sc, Ba, La, Ce, Eu, and Pr may also be slightly underabundant; (2) there is a possibility that Na may be slightly overabundant and the rare earths slightly underabundant in all three stars. The observational data are used to provide a mean curve of growth and log,' values for future differential curve-of-growth analyses of K giants, using the Hyades K giants as reference stars. This mean curve of growth is necessarily bifurcated. The mean curve of growth and the K star log,' values have been applied to analysis of abundances in O Tauri and in 6 Virginis. The abundances found for O Tauri agree with the abundances found for the other Hyades K giants and the abundances found for 6 Virginis agree with those found by Cayrel and Cayrel (1963).