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

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.

Based on observations collected with the NASA/ESA HST (Prop. 11685, 12517, 13410, and 15403 ), obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.