Cluster AgeS Experiment ( CASE ) : RR Lyrae stars from the globular cluster ω Centauri as standard candles

New photometry of RRab and RRc stars in ω Cen is used to calibrate their absolute magnitudes M V as a function of: a) metallicity; and b) the Fourier parameters of light curves in the V band. The zero point of both calibrations relies on the distance modulus to the cluster derived earlier by the CASE project based on observations of the detached eclipsing binary OGLE GC17. For RRab variables we obtained a relation of M V = (0.26 ± 0.08)[Fe/H] + (0.91 ± 0.13). A dereddened distance modulus to the LMC based on that formula is µ 0 = 18.56 ± 0.14 mag. The second calibration of M V , which is based on Fourier coefficients of decomposed light curves, results in the LMC distance of µ 0 = 18.51 ± 0.07 mag.