High-resolution extinction map in the direction of the bulge globular cluster NGC 6440

TL;DR

This study presents the first high-resolution optical extinction map of NGC 6440, revealing patchy dust structures and improving the clarity of the cluster's color-magnitude diagram through proper motion analysis and differential reddening correction.

Contribution

It provides the first detailed high-resolution extinction map of NGC 6440, enhancing understanding of dust structures and cluster properties in the Galactic bulge.

Findings

Detected patchy and filamentary dust structures with extinction variations up to 0.5 mag.

Improved the color-magnitude diagram of NGC 6440 after decontamination and reddening correction.

Identified cluster members using proper motion analysis.

Abstract

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.