Transformations between the WISE, 2MASS, SDSS and BVRI photometric systems - I. Transformation equations for dwarfs

We present colour transformations for the conversion of the W1 and W2 magnitudes of the Wide-field Infrared Survey Explorer (WISE) photometric system to the Johnson-Cousins BVRI, Sloan Digital Sky Survey gri and Two-Micron All-Sky Survey JHK s photometric systems, for dwarfs. The W3 and W4 magnitudes were not considered due to their insufficient signal-to-noise ratio (S/N). The coordinates of 825 dwarfs along with their BVRI, gri and JHK s data taken from Bilir et al. were matched with the coordinates of stars in the preliminary data release of the WISE, and a homogeneous dwarf sample with high S/N had been obtained using the following constraints: (1) the data were dereddened; (2) giants were identified and excluded from the sample; (3) sample stars were selected according to data quality; (4) transformations were derived for subsamples of different metallicity ranges; and (5) transformations were two-colour-dependent. These colour transformations, coupled with known absolute magnitudes at shorter wavelengths, can be used in space-density evaluation for the Galactic (thin and thick) discs, at distances larger than the ones evaluated with JHK s photometry.