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

Wide-field BVI photometry and 12CO (1 → 0) observations are presented in the region of the open cluster NGC 6520 and the dark molecular cloud Barnard 86. From the analysis of the optical data we find that the cluster is rather compact, with a radius of 1.′0 ± 0.′5, smaller than previous estimates. The cluster age is 150 ± 50 Myr, and the reddening E B-V = 0.42 ± 0.10. The distance from the Sun is estimated to be 1900 ± 100 pc, which is larger than previous estimates. We finally derive basic properties of the dark nebula Barnard 86 on the assumption that it lies at the same distance as the cluster. © 2005. The American Astronomical Society. All rights reserved.