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S.C. Schuler, J.R. King (Clemson Univ.), L.M. Hobbs (Yerkes Obs.), M.H. Pinsonneault (Ohio State Univ.)
We analyze the high-excitation 7774 \; \mathrm{Å} \ion{O}{1} triplet in high-resolution, moderate signal-to-noise spectra of 15 Pleiades (HET/HRS) and 8 M34 (Keck/HIRES) open cluster dwarfs. Effective temperatures range from 5048 - 6172 K for the Pleiades sample and from 5290 - 6130 K for the M34 sample. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids: with convective overshoot, without convective overshoot, with the mixing length parameter set to 0.5, and with the convective treatment of Canuto, Goldman, & Mazzitelli. In contrast to existing NLTE predictions, a dramatic increase in \ion{O}{1} triplet abundance with \textit{decreasing} temperature is seen for both clusters, regardless of atmospheric model. \ion{S}{1} abundances of three Pleiads derived from the high-excitation \lambda 6052.67 feature mimic the \ion{O}{1} abundance behavior. O abundances have also been derived from the 6300 {Å} [OI] feature in three Pleiads; the abundances exhibit a much lower mean-value than the cool dwarf triplet results. Inasmuch as the [OI] abundances are presumed to be free from NLTE effects, their mean (\mathrm{[O/H]}6300 = 0.14) provide the current best estimate of the Pleiades O abundance. Spreads in \mathrm{[O/H]}Trip at a given temperature are also seen in both clusters; there is no correlation between the spreads and chromospheric activity measures.
This study is supported by a Graduate Student Research Fellowship from the South Carolina Space Grant Consortium and by grants AST 00-86576 and AST 02-39518 awarded to J.R.K. from the National Science Foundation.
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The author(s) of this abstract have provided an email address for comments about the abstract: sschule@ces.clemson.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.