The VVV survey: Long-period variable stars I. Photometric catalog of ten
  VVV/OGLE tiles
  Long-period variable stars (LPVs) are pulsating red giants, primarily in the
asymptotic giant branch phase, and they include both Miras and semi-regular
variables (SRVs). Their period-age and period-luminosity relations enable us to
trace different stellar populations, as they are intrinsically very bright and
cover a wide range in distances and ages. The purpose of this study is to
establish a census of LPV stars in a region close to the Galactic center, using
the six-year database of the Vista Variables in the V\'ia L\'actea (VVV) ESO
Public Survey, as well as to describe the methodology that was employed to
search for and characterize LPVs using VVV data. Near-IR surveys such as VVV
provide a unique opportunity to probe the high-extinction innermost regions of
the Milky Way. The detection and analysis of the intrinsically bright Miras in
this region could provide us with an excellent probe of the properties of the
Milky Way far behind its bulge. We used point-spread function photometry for
all available $K_{s}$-band images in ten VVV tiles, covering $16.4~\deg^2$ in
total, overlapping fields observed in the course of the Optical Gravitational
Lensing Experiment (OGLE)-III survey. We designed a method to select LPV
candidates, and we used the known variables from OGLE-III and other known
variables from the literature to test our approach. The reduced $\chi^2$
statistic, along with the flux-independent index $K_{(fi)}$, were used in our
analysis. The Lomb-Scargle period search method, Fourier analysis, template
fitting, and visual inspection were then performed to refine our sample and
characterize the properties of the stars included in our catalog. A final
sample of 130 Mira candidates, of which 129 are new discoveries, was thus
obtained, with periods in the range between about 80 and 1400~days.
