The Distribution of the Elements in the Galactic Disk

This paper reports on the spectroscopic investigation of 54 Cepheids, deriving parameters and abundances. These Cepheids extend previous samples by about 35% in number and increase the amount of the Galactic disk coverage, especially in the direction of l ≈ 120°. We find that there exists in the Galactic disk at that longitude and at a solar distance of about 3-4 kpc a region that has enhanced abundances, ⟨Fe/H]⟩ ≈ +0.2, with respect to the local region. A simple linear fit to all Cepheid data now extant yields a gradient d [Fe/H]/ dR G = -0.068 ± 0.003 dex kpc -1 . After consideration of the spatial abundance inhomogeneities in the sample, we conclude that the best current estimate of the overall gradient is d [Fe/H]/ dR G = -0.06 dex kpc -1 .