The Open Cluster NGC 6520 and the Nearby Dark Molecular Cloud Barnard 86

Wide field BVI photometry and $^{12}$CO(1$\to$0) observations are presen tedin the region of the open cluster NGC 6520 and the dark molecular cloudBarnard~86. From the analysis of the optical data we find that the cluster israther compact, with a radius of 1.0$\pm$0.5 arcmin, smaller than previousestimates. The cluster age is 150$\pm$50 Myr and the reddeningE$_{B-V}$=0.42$\pm$0.10. The distance from the Sun is estimated to be1900$\pm$100 pc, and it is larger than previous estimates. We finally derivebasic properties of the dark nebula Barnard 86 on the assumption that it liesat the same distance of the cluster.Comment: 21 pages, 8 eps figures (a few degraded in resolution), accepted for publication in the Astronomical Journa