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We present the results of our abundance analysis of Fe, Ni, and O in highS/N, high-resolution VLT/UVES and McDonald/2dcoude spectra of nine dwarfs andthree giants in the Hyades open cluster. The difference in Fe abundancesderived from Fe II and Fe I lines ([Fe II/H] - [Fe I/H]) and Ni I abundancesderived from moderately high-excitation (Chi ~ 4.20 eV) lines are found toincrease with decreasing T_eff for the dwarfs. Both of these findings are inconcordance with previous results of over-excitation/ionization in cool youngdwarfs. Oxygen abundances are derived from the Lambda 6300 [O I] line, withcareful attention given to the Ni I blend. The dwarf O abundances are instar-to-star agreement within uncertainties, but the abundances of the threecoolest dwarfs (4573 < T_eff < 4834 K) evince an increase with decreasingT_eff. Possible causes for the apparent trend are considered, including theeffects of over-dissociation of O-containing molecules. O abundances arederived from the near-UV Lambda 3167 OH line in high-quality Keck/HIRESspectra, and no such effects are found- indeed, the OH-based abundances show anincrease with decreasing T_eff, leaving the nature and reality of the cooldwarf [O I]-based O trend uncertain. The mean relative O abundance of the sixwarmest dwarfs (5075 < T_eff < 5978 K) is [O/H] = +0.14 +/- 0.02, and we find amean abundance of [O/H] = +0.08 +/- 0.02 for the giants. Thus, our updatedanalysis of the Lambda 6300 [O I] line does not confirm the Hyades giant-dwarfoxygen discrepancy initially reported by King & Hiltgen (1996), suggesting thediscrepancy was a consequence of analysis-related systematic errors....

Hyades Oxygen Abundances from the Lambda 6300 [O I] Line: The Giant-Dwarf Discrepancy Revisited