A differential study of the oxygen abundances in the Galactic thin and thick disks

Abstract

First results from a study into the abundance trends of oxygen in the Galactic thin and thick disks are presented. Oxygen abundances for 63 nearby F and G dwarf stars, based on very high resolution spectra ($R\sim215 000$) and high signal-to-noise ($S/N>400$) of the faint forbidden oxygen line at 6300 Å, have been determined. Our findings can be summarized as follows: {\bf 1)} at $\rm [Fe/H]<0$ the oxygen trends in the thin and thick disk are smooth and distinct, indicating their different origins, {\bf 2)} $\rm [O/Fe]$ for the thick disk stars show a turn-over at [Fe/H]$\sim -0.35$, indicating the peak of the enrichment from SNe type Ia to the interstellar medium, {\bf 3)} the thin disk stars show a shallow decrease going from $\rm [Fe/H] \sim -0.7$ to the highest metallicities with no apparent turn-over present indicating a more quiet star formation history, and {\bf 4)} $\rm [O/Fe]$ continues to decrease at $\rm [Fe/H]>0$ without showing the leveling out that previously has been seen.