Variability and stellar populations with deep optical-IR images of the
  Milky Way disk: matching VVV with VLT/VIMOS data
  We have used deep V-band and JHKs-band observations to investigate
variability and stellar populations near the Galactic plane in Centaurus, and
compared the observations with the Galactic model of Besancon. By applying
image subtraction technique to a series of over 580 V-band frames taken with
the ESO VLT/VIMOS instrument during two contiguous nights in April 2005, we
have detected 333 variables among 84,734 stars in the brightness range
12.7<V<26.0 mag. Infrared data collected in March 2010 with the new ESO VISTA
telescope allowed us to construct deep combined optical-IR colour-magnitude and
colour-colour diagrams. All detected variables but four transit candidates are
reported for the first time. The majority of the variables are
eclipsing/ellipsoidal binaries and delta Scuti-type pulsators. The occurrence
rate of eclipsing/ellipsoidal variables reached ~0.28% of all stars. This is
very close to the highest fraction of binary systems detected using
ground-based data so far (0.30%), but still about four times less than the
average occurrence rate recently obtained from the Kepler space mission after
44 days of operation. Comparison of the observed Ks vs. V-Ks diagram with a
diagram based on the Besancon model shows significant effects of both distance
and reddening in the investigated direction of the sky. We demonstrate that the
best model indicates the presence of absorbing clouds at distances 11-13 kpc
from the Sun in the minor Carina-Sagittarius Arm.
