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Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4are derived from a non-LTE analysis of the 777 nm O I triplet lines. Thesestars have precise atmospheric parameters measured by Nissen and Schuster, whofind that they separate into three groups based on their kinematics andalpha-element (Mg, Si, Ca, Ti) abundances: thick-disk, high-alpha halo, andlow-alpha halo. We find the oxygen abundance trends of thick-disk andhigh-alpha halo stars very similar. The low-alpha stars show a largerstar-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically loweroxygen abundances compared to the other two groups. Thus, we find the behaviorof oxygen abundances in these groups of stars similar to that of the alphaelements. We use previously published oxygen abundance data of disk and verymetal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygenabundance trends of stars in the solar neighborhood. Two field halo dwarf starsstand out in their O and Na abundances. Both G53-41 and G150-40 have very lowoxygen and very high sodium abundances, which are key signatures of theabundance anomalies observed in globular cluster (GC) stars. Therefore, theyare likely field halo stars born in GCs. If true, we estimate that at least3+/-2% of the local field metal-poor star population was born in GCs.

Oxygen abundances in low- and high-alpha field halo stars and the discovery of two field stars born in globular clusters