Carbon, nitrogen, and oxygen abundances in main-sequence stars. I - Procyon and the Hyades cluster stars 45 Tauri and HD 27561

Abstract

High signal-to-noise observations of C I, N I, and O I lines in the near-infrared spectra of Procyon and the Hyades cluster main-sequence stars 45 Tau and HD 27561 have been analyzed to determine their carbon, nitrogen, and oxygen abundances. The carbon, nitrogen, and oxygen abundances of all three stars are solar. The estimated uncertainty of the abundances is +- 0.2 dex. Analysis of observations of the forbidden carbon and oxygen lines, CH blue system (0,0) and (1,1) band lines, and CN violet system (0,0) band lines in Procyon provides a check of the results obtained from the permitted atomic lines.The solar C/N ratio of the Hyades cluster dwarfs allows the less-than-solar C/N ratio of the Hyades giants recently determined by Lambert and Ries to be unambiguously interpreted as the effect of CNO cycle processing during the giants' main-sequence lifetime.The iron abundances of Procyon, 45 Tau, and HD 27561 derived from the equivalent widths of Fe I and Fe II lines are found to be solar. This result is consistent with previous spectroscopic determinations of the iron abundance of Hyades cluster stars. The discrepancy between the spectroscopic determinations of a solar metal content of the Hyades and the metal richnessmore » inferred from photometry is discussed.« less