CHEMICAL ABUNDANCES FOR F-LUMINOSITY AND G-LUMINOSITY CLASS-II STARS

Stellar parameters and abundances for a sample of 38 F/G held bright g iants have been determined based on high-resolution and high signal-to -noise KPNO coude spectra. This study was designed to complement CNO a bundance studies of supergiants and giants which bracket the present s tars in mass. The pertinent results of the present study are: The brig ht giants have [Fe/H] ratios which are solar and are in good agreement with the [Fe/H] ratios found in supergiants and giants. The lithium a bundances ate diluted in most stars with respect to the canonical inte rstellar disk value and the lithium abundances correlate with effectiv e temperature. The CNO abundances of all of the stars show the effects of nuclear processing though to different degrees: the stars are carb on deficient and nitrogen enhanced. The [O/Fe] ratio in these stars in subsolar with an average value of similar to-0.3 dex. The [O/Fe] rati o correlates with the [C/Fe] ratio. All of these effects are also pres ent in the Li and CNO abundances of supergiants and giants. The implic ation of these results is that the standard model of stellar mixing is deficient and that new evolutionary models are needed incorporating s uch effects as rotationally driven mixing and diffusion. (C) 1995 Amer ican Astronomical Society.