Forbidden oxygen in the Milky Way disk

Sammanfattning: Oxygen is produced inside massive stars and dispersed into the interstellar medium mainly through type II supernovae explosions. This element, which is the third most abundant one in the Universe, plays an important role in tracing the Galactic chemical history and evolution. This study aims at determining oxygen abundances from a sample of 714 F and G dwarf stars located in the solar neighborhood, from the oxygen forbidden line located at 630 nm, which is very weak and blended with a nickel line. This sample has been already used for a similar study (Bensby 2014), but abundances were determined via the triplet oxygen lines found at 777,4 nm, which are strong but formed under Non-Local Thermodynamic Equilibrium (NLTE) conditions. However, these departures were corrected for with empirical methods. Therefore, the resulting oxygen abundances from the forbidden line were compared to those obtained from the triplets, to test the reliability of this indicator within the sample of 714 stars. High-resolution spectra of these stars were obtained with high signal-to-noise, from observations conducted at some of the World's largest telescopes. Abundances for oxygen were calculated by spectral fitting of the observed and synthetic spectra using LTE model atmospheres obtained from MARCS. We find that the forbidden line was not a reliable indicator for determining oxygen abundances from the 714 stars sample, in comparison with the 777,4 nm.