The Metallicity Gradient in the Galactic Disk Revealed by Cepheids and Open Clusters

摘要

We have collected results from individual observations of metallicities of Cepheids and open clusters from the literature in order to investigate the [Fe/H] gradient in the Galactic disk. We re-computed the distances of the Cepheids based on the period-luminosity and period-intrinsic color relations, and the distances of open clusters with more precise ways of computing the effect of interstellar extinction. The data obtained were analyzed using the short distance scale of the galactocentric distance of the Sun, R_0= 7.5 kpc. We have concentrated our study on the Galactic distributions of [Fe/H]. We discuss the existence of a sudden step down in metallicity at a galactic radius of about 8.6kpc, followed by a relatively flat region, and we report the existence of an azimuthal gradient. The same break in the metallicity gradient was previously presented by other authors, and it has been detected in samples of other objects as well. We also discuss two different hypotheses for this feature, which both are based on the connection between the spiral structure and star-formation rate of the Galaxy.