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