High-resolution Extinction Map in the Direction of the Bulge Globular Cluster NGC 6440*

Abstract

Abstract We used optical images acquired with the UVIS channel of the Wide Field Camera 3 on board the Hubble Space Telescope to construct the first high-resolution extinction map in the direction of NGC 6440, a globular cluster located in the bulge of our Galaxy. The map has a spatial resolution of 0.″5 over a rectangular region of about 160″ × 240″ around the cluster center, with the long side in the northwest/southeast direction. We found that the absorption clouds show patchy and filamentary substructures with extinction variations as large as δE(B − V) ∼0.5 mag. We also performed a first-order proper motion analysis to distinguish cluster members from field interlopers. After the field decontamination and the differential reddening correction, the cluster sequences in the color–magnitude diagram appear much better defined, providing the best optical color–magnitude diagram so far available for this cluster.