Chemical Abundances for Very Strong-Lined Giants

Stellar parameters and abundances for a sample of 55 U/K field giants of which 22 are normal stars and the other 33 are classified as VSL (very strong-lined) have been determined based on high-resolution and high signal-to-noise KPNO coudé spectra. The primary pertinent points of comparison between these stars are: VSL stars have [Fe/H] ratios that average +0.1 dex relative to normal giants; VSL stars are modestly carbon and nitrogen rich relative to the normal stars. The mean difference in [C/Fe] is +0.1 and for [N/Fe] is +0.05; the [O/Fe] ratios of the normal and VSL stars are comparable; the lithium abundances, ¹²C/¹³C ratios, and [M/Fe] ratio for Z > 10 are comparable in the two groups. The combination of the first through third points is sufficient to explain the difference in VSL and normal U/K giant spectra. Our preferred interpretation of the VSL stars is that they are the result of normal evolution of a dwarf whose initial composition is somewhat metal and carbon rich. The fraction of stars with these properties is consistent with the number of VSL giants.