Milky Way Demographics with the VVV Survey II. Color Transformations and Near-Infrared Photometry for 136 Million Stars in the Southern Galactic Disk

TL;DR

This paper develops color transformation equations for VVV near-infrared data to align with 2MASS, enabling detailed studies of the Galactic disk and providing a precise reddening law crucial for astrophysical research.

Contribution

It introduces new transformation equations for VVV JHKs photometry onto the 2MASS system and derives the most precise reddening law to date for the Galactic disk.

Findings

Transformation coefficients depend on extinction variables.

Established a mean reddening law of E_{J-H}/E_{H-Ks}=2.13 +/- 0.04.

Enhanced the utility of VVV data for Galactic structure studies.

Abstract

The new multi-epoch near-infrared VVV survey (VISTA Variables in the Via Lactea) is sampling 562 sq. deg 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 JHKs 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 E_{J-H}/E_{H-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.