Milky Way demographics with the VVV survey II. Color transformations and near-infrared photometry for 136 million stars in the southern Galactic disk

The new multi-epoch near-infrared VISTA Variables in the Via Lactea (VVV) survey is sampling 562 deg(2) of the Galactic bulge and adjacent regions of the disk. Accurate astrometry established for the region surveyed allows the VVV data to be merged with overlapping surveys (e. g., GLIMPSE, WISE, 2MASS, etc.), thereby enabling the construction of longer baseline spectral energy distributions for astronomical targets. However, in order to maximize use of the VVV data, a set of transformation equations are required to place the VVV JHK(s) photometry onto the 2MASS system. The impetus for this work is to develop those transformations via a comparison of 2MASS targets in 152 VVV fields sampling the Galactic disk. The transformation coefficients derived exhibit a reliance on variables such as extinction. The transformed data were subsequently employed to establish a mean reddening law of EJ-H/EH-Ks = 2.13 +/- 0.04, which is the most precise determination to date and merely emphasizes the pertinence of the VVV data for determining such important parameters.