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2004ApJ...602L.117S - Astrophys. J., 602, L117-L120 (2004/February-3)

Oxygen in open cluster dwarfs: Pleiades and M34.


Abstract (from CDS):

We analyze the high-excitation O I λ7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation λ6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] λ6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]6300=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]Tripat a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures.

Abstract Copyright:

Journal keyword(s): Galaxy: Open Clusters and Associations: Individual: Messier Number: M34 - Galaxy: Open Clusters and Associations: Individual: Name: Pleiades - Stars: Abundances - Stars: Atmospheres - Stars: Late-Type - Stars: Population II

VizieR on-line data: <Available at CDS (J/ApJ/602/L117): table1.dat>

Simbad objects: 26

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