Carbon, nitrogen, and oxygen abundances of selected stars in the Hertzsprung gap

The iron, carbon, nitrogen, and oxygen abundances for several stars whose characteristics place them in the Hertzsprung gap have been derived from high-resolution spectra. These stars were selected based on the fact that previous studies have shown them to have peculiar carbon, nitrogen, or lithium abundances considering their position in the Hertzsprung-Russell diagram. When combined with the lithium abundances derived by Wallerstein and coworkers, the carbon, nitrogen, and oxygen abundances indicate that the sample of stars can generally be broken into two categories-lower luminosity dwarfs or subgiants that are unmixed and higher luminosity mixed giants, Among the sample are two stars, HR 7606 and HR 8626, which previously have been identified by Bidelman as "low-velocity CH stars." These stars show metallicities of [Fe/H] similar to -0.5 and solar abundances of carbon, nitrogen, and oxygen. The strength of the CPI band in these stars is probably an artifact of a mild metal deficiency and the absence of substantial mixing of CN processed materials to the surface of the star rather than an unusual nucleosynthetic history.