Oxygen Abundance of Open Cluster Dwarfs

We present oxygen abundances of dwarfs in the young open cluster IC 4665deduced from the OI $\lambda$7774 triplet lines and of dwarfs in the opencluster Pleiades derived from the [OI] $\lambda$6300 forbidden line. Stellarparameters and oxygen abundances were derived using the spectroscopic synthesistool SME (Spectroscopy Made Easy). We find a dramatic increase in the upperboundary of the OI triplet abundances with decreasing temperature in the dwarfsof IC 4665, consistent with the trend found by Schuler et al. in the openclusters Pleiades and M 34, and to a less extent in the cool dwarfs of Hyades(Schuler et al. 2006a) and UMa (King & Schuler 2005). By contrast, oxygenabundances derived from the [OI] $\lambda$6300 forbidden line for stars inPleiades and Hyades (Schuler et al. 2006b) are constant within the errors.Possible mechanisms that may lead a varying oxygen triplet line abundance areexamined, including systematic errors in the stellar parameter determinations,the NLTE effects, surface activities and granulation. The age-related effectsstellar surface activities (especially the chromospheric activities) aresuggested by our analysis to blame for the large spreads of oxygen triplet lineabundances.Comment: 11 pages, 5 figures. ApJ in pres