The Galactic Oxygen Abundance Gradient

We have previously published medium- to high-resolution spectroscopic observations of early B-type main-sequence objects, lying in 18 young, stellar clusters and associations or the general disk population, over galactocentric distances 6 ≲ R g ≲ 18 kpc. Using a homogeneous subset of stars with similar atmospheric parameters, we have reanalyzed the O II line spectra using non-LTE line formation calculations. We derive an oxygen abundance gradient of -0.07 ± 0.01 dex kpc -1 , which should be representative of the present-day interstellar medium within the Galaxy. This extensive and self-consistent data set represents a considerable advance on previous attempts to measure the Galactic oxygen abundance gradient using early-type stars and produces a significant gradient for the first time. The outer disk is well sampled, which gives the result statistical significance, and the discrepancies with previous similar studies are discussed. We compare this new result to those derived using Galactic H II regions and planetary nebulae and conclude that the different methods now appear to produce consistent agreement.