About Metallicity Variations in the Local Galactic Interstellar Medium
  In this paper we discuss and confront recent results on metallicity
variations in the local interstellar medium, obtained from observations of HII
regions and neutral clouds of the Galactic thin disk, and compare them with
recent high-quality metallicity determinations of other tracers of the chemical
composition of the interstellar medium as B-type stars, classical Cepheids and
young clusters. We find that the metallicity variations obtained for these last
kinds of objects are consistent with each other and with that obtained for HII
regions but significantly smaller than those obtained for neutral clouds. We
also discuss the presence of a large population of low-metallicity clouds as
the possible origin for large metallicity variations in the local Galactic thin
disk. We find that such hypothesis does not seem compatible with: (a) what is
predicted by theoretical studies of gas mixing in galactic disks, and (b) the
models and observations on the metallicity of high-velocity clouds and its
evolution as they mix with the surrounding medium in their fall onto the
Galactic plane. We conclude that that most of the evidence favors that the
chemical composition of the interstellar medium in the solar neighborhood is
highly homogeneous.
