Transformation equations between GALEX and UBV photometric systems

The insufficiency of photometric data in the U-band of the FGK-type stars in the solar neighborhood makes difficult to determine the flux of the blue region of their spectral energy distributions, and causes to the inadequacy in the estimation of the photometric metallicity and the color excesses of these stars. To overcome this problem, the U-V color indices of 556 stars in different luminosity class, whose spectroscopic, photometric and astrometric data are well known, were calculated using derived transformation equations sensitive to GALEX and BV color indices. In order to obtain the transformation equations, GALEX DR7 FUV, NUV and Johnson-Morgan UBV photometric data were used. Model atmosphere parameters (Teff, log g, [Fe/H]) collected from the literature concerning the stars were separated into different metal abundance intervals and HR diagrams were created. Then PARSEC mass tracks were added to these HR diagrams to determine the luminosity classes of the stars in the sample. The transformation equations, which were designed based on two color indices, were derived for stars in different luminosity classes. The analyses showed that U-V color index calculations performed by the newly obtained photometric transformation equations, provide highly sensitive results (Δ(U−V)0 ∼0.05 mag).