High-resolution extinction map in the direction of the strongly obscured
  bulge fossil fragment Liller 1
  We used optical images acquired with the Wide Field Camera of the Advanced
Camera for Surveys onboard the Hubble Space Telescope and near-infrared data
from GeMS/GSAOI to construct a high-resolution extinction map in the direction
of the bulge stellar system Liller 1. In spite of its appearance of a globular
cluster, Liller 1 has been recently found to harbor two stellar populations
with remarkably different ages, and it is the second complex stellar system
with similar properties (after Terzan5) discovered in the bulge, thus defining
a new class of objects: the Bulge Fossil Fragments. Because of its location in
the inner bulge of the Milky Way, very close to the Galactic plane, Liller 1 is
strongly affected by large and variable extinction. The simultaneous study of
both the optical and the near-infrared color-magnitude diagrams revealed that
the extinction coefficient R$_V$ in the direction of Liller 1 has a much
smaller value than commonly assumed for diffuse interstellar medium (R$_V=2.5$,
instead of 3.1), in agreement with previous findings along different light
paths to the Galactic bulge. The derived differential reddening map has a
spatial resolution ranging from $1''$ to $3''$ over a field of view of about
$90''$X$90''$. We found that the absorption clouds show patchy sub-structures
with extinction variations as large as $\delta {\rm E}(B-V)\sim0.9$ mag.
