High-resolution extinction map in the direction of the bulge globular
  cluster NGC 6440
  We used optical images acquired with the UVIS channel of the Wide Field
Camera 3 on board of 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" X 240" around the cluster center, with
the long side in the North-West/South-East direction. We found that the
absorption clouds show patchy and filamentary sub-structures with extinction
variations as large as $\delta {\rm E}(B-V)\sim0.5$ 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.
