  We present oxygen abundances of dwarfs in the young open cluster IC 4665
deduced from the OI $\lambda$7774 triplet lines and of dwarfs in the open
cluster Pleiades derived from the [OI] $\lambda$6300 forbidden line. Stellar
parameters and oxygen abundances were derived using the spectroscopic synthesis
tool SME (Spectroscopy Made Easy). We find a dramatic increase in the upper
boundary of the OI triplet abundances with decreasing temperature in the dwarfs
of IC 4665, consistent with the trend found by Schuler et al. in the open
clusters 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, oxygen
abundances derived from the [OI] $\lambda$6300 forbidden line for stars in
Pleiades and Hyades (Schuler et al. 2006b) are constant within the errors.
Possible mechanisms that may lead a varying oxygen triplet line abundance are
examined, including systematic errors in the stellar parameter determinations,
the NLTE effects, surface activities and granulation. The age-related effects
stellar surface activities (especially the chromospheric activities) are
suggested by our analysis to blame for the large spreads of oxygen triplet line
abundances.
