1997A&A...322..218K

We use B and V data of globular cluster variables to derive a formula for the distance moduli of RRab stars. The method employs the Fourier decomposition of the V light curve and the average B-V colour index. By using our former result for the V₀ absolute magnitude, we also obtain an expression for the dereddened colour index. With the aid of the new formulae, the relative distance moduli can be estimated within an error of <0.03mag. Although we also make an absolute calibration, it is cautioned that this may be more affected by possible systematic errors originating mostly from the Baade-Wesselink magnitudes. On the basis of the scatter of the individual distance moduli computed with and without reddening correction, it is shown that inhomogeneous reddening plays a role in several clusters. By using our formulae we derive new expressions for the I_c and K absolute magnitudes on a sample of stars which contains mostly field stars with accurate photometry. As a by-product of this derivation we also give optimum estimations for the selective absorption coefficient R_V. We show that the K absolute magnitude contains important contribution also from the Fourier parameters, besides the well known dependence on the period. The I_c absolute magnitude is superbly correlated with the Fourier parameters, which implies that this colour is a very good candidate for the accurate estimation of the absolute magnitude.