Oxygen abundance distribution in the Galactic disc

Weperformedanon-localthermodynamicequilibrium(NLTE)analysisoftheinfraredoxygen tripletforalargenumberofCepheidspectraobtainedwiththeHobby–EberlyTelescope.These data were combined with our previous NLTE results for stars observed with the Max Planck Gesellschaft Telescope with the aim of investigating the oxygen abundance distribution in the Galactic thin disc. We found the slope of the radial (O/H) distribution to be equal −0.058 dexkpc −1 . However, we found some evidence that the distribution might become flatter in the outer parts of the disc. This is supported by the results of other authors who have studied open clusters, planetary nebulae and H II regions. Some mechanisms of flattening are discussed.