Abstract:
In this work, we analysed high resolution spectra of a large sample of OB stars located in the Galactic disk aimed to study the distribution of the projected stellar rotation (vseni) and the radial distribution of chemical abundances of the Galactic outer disk. The vseni distribution of the Galactic OB stars is bimodal. By splitting the sample stars in objects belonging to the field, association or to clusters, we note that the distribution of vseni is different for each subset, and the mean vseni of the field stars is lower than the value for the cluster's stars. Possible explanations for the observed difference include different evolutionary stages for each subset of stars or different densites of the progenitor cloud of these stars. Our vseni results can be described by two maxwellian distributions with a trend that the mean \vseni\ of cluster's stars are larger than the values for the field stars. The abundance distribution in the Galactic disk is characterized by a decrease of the abundances along the Galactic radius (radial gradient), which is a key parameter to constrain chemical evolution models of the Galaxy. We developed a methodology based on non-LTE spectral synthesis aimed to obtaining the stellar parameters, including the abundances of silicon and oxygen. Our abundance results suggest radial gradients of -0.065 and -0.054 dex/kpc for silicon and oxygen, respectively. The standard procedure to define the radial gradient is usually based on one linear regression, however some authors suggest that a model with two linear regressions with a descontinuity at approximately 10 kpc of the Galactic center would be a better description of the radial gradient. We did not find evidences that our data would be better described by a two-zone model radial gradient.
