The population in the background of open clusters: tracer of the Norma-Cygnus arm

Abstract

We present colour-magnitude diagrams of open clusters, located in the range $112^\circ < l < 252^\circ$, manifesting stellar populations in the background of clusters. Some of the populations are found to be located beyond the Perseus arm and may be the part of Norma-Cygnus (outer) arm. The outer arm seems to be continued from $l\sim120^\circ$ to $l\sim235^\circ$. The background populations follow the downward warp of the Galactic plane around $l\sim240^\circ$.