λ7774 Oxygen Triplet in Open Cluster Dwarfs: Pleiades and M34
✍ Scribed by S.C. Schuler; J.R. King; L.M. Hobbs; M.H. Pinsonneault
- Publisher
- Elsevier Science
- Year
- 2005
- Tongue
- English
- Weight
- 120 KB
- Volume
- 758
- Category
- Article
- ISSN
- 0375-9474
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✦ Synopsis
We have undertaken a LTE analysis of the high-excitation 7774 Å O I 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 AT-LAS9 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 O I triplet abundance with decreasing temperature is seen for both clusters, regardless of atmospheric model. S I abundances of three Pleiads derived from the high-excitation λ6052.67 feature mimic the O I 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. These data suggest LTE abundances derived from the O I triplet for cool dwarfs (T eff ≤ 5800 K) should be viewed with caution.