STELLAR OXYGEN ABUNDANCES .5. ABUNDANCES OF 2 HYADES DWARFS DERIVED FROM THE 6300-ANGSTROM [O-I] LINE

We present observations of the 6300 Angstrom [O I] spectral region in two cool Hyades dwarfs, vB 79 and vB 25. We derive a mean iron abundan ce, [Fe/H]similar to+0.11, in good agreement with recent analyses of F and G Hyades dwarfs. The O abundance derived from spectrum synthesis, [O/H]similar to+0.15, is between the values deduced by Garcia Lopez e t al. (1993, ApJ, 412, 173; [O/H]=-0.05 to -0.10) and King (1993, Ph. D. Dissertation, University of Hawaii; [O/H]=+0.26), who employed the 7774 Angstrom O I triplet in hotter Hyades dwarfs. An accounting of di fferences between these two 7774 Angstrom analyses is given. Our [O I] -based determination suggests the Hyades O abundance itself is super-s olar, though [O/Fe]similar to 0.0; however, systematic errors as large as 0.10-0.15 dex cannot be ruled out. The Hyades giants show an unexp ected similar to 0.23 dex O deficit relative to our dwarf value. While some suggestive evidence for non-standard nuclear processing and mixi ng in the Hyades giants may exist, we find it unconvincing. Rather, mo del atmosphere deficiencies or [O I]-region blending features that are still unrecognized by laboratory and theoretical efforts may contribu te to the giant-dwarf O discrepancy. Finally, our high O abundance is marginally consistent with values claimed to provide a solution to the Hyades Li problem from standard stellar models. However, it is not cl ear that these models do in fact reproduce the extant Li data. Our Li abundance upper limit for vB 25 is at least 0.5 dex lower than the abu ndances of two tidally locked binaries of similar T-eff. Standard stel lar models of uniform composition and age are not able to reproduce su ch scatter in Li. (C) 1996 American Astronomical Society.