Candidate star clusters toward the inner Milky Way discovered on
  deep-stacked Ks-band images from the VVV Survey
  The census of star clusters in the inner Milky Way is incomplete because of
extinction and crowding. We embarked on a program to expand the star cluster
list in the direction of the inner Milky Way using deep stacks of Ks-band
images from the VISTA Variables in Via Lactea (VVV) Survey. We applied an
automated two-step procedure to the point-source catalog derived from the deep
Ks images: first, we identified overdensities of stars, and then we selected
only candidate clusters with probable member stars that match an isochrone with
a certain age, distance, and extinction on the color-magnitude diagram. This
pilot project only investigates the cluster population in part of one VVV tile,
that is, b201. We identified nine cluster candidates and estimated their
parameters. The new candidates are compact with a typical radius on the sky of
~0.2--0.4 arcmin (~0.4-1.6 pc at their estimated distances). They are located
at distances of ~5-14 kpc from the Sun and are subject to moderate extinction
of E(B-V)=0.4-1.0 mag. They are sparse, probably evolved, with typical ages
log(t/1 yr)~9. Based on the locations of the objects inside the Milky Way, we
conclude that one of these objects is probably associated with the disk or halo
and the remaining objects are associated with the bulge or the halo. The
cluster candidates reported here push the VVV Survey cluster detection to the
limit. These new objects demonstrate that the VVV survey has the potential to
identify thousands of additional cluster candidates. The sub-arcsec angular
resolution nd the near-infrared wavelength regimen give it a critical advantage
over other surveys.
