The distance modulus of the Large Magellanic Cloud based on double-mode RR Lyrae stars

We use double-mode RR Lyrae (RRd) stars from the macho variable star database of the Large Magellanic Cloud (LMC) to estimate its distance, by utilizing photometric data, linear pulsation and stellar atmosphere models. If we set EB−V = 0.11 and [M/H]= −1.5 for LMC, we get M − m = 18.52 mag, which is in agreement with the value obtained from Galactic cluster RRd stars. Although the formal statistical error (standard deviation) of M − m derived from the macho set is only 0.024 mag, the systematic errors are more substantial. These errors are mostly due to the zero point ambiguity of the temperature scale and to the error of the photometric calibration. However, the fact that the distance moduli obtained in this and in our former studies of cluster RRd and Small Magellanic Cloud beat Cepheids agree so well, implies that the only serious source of error is the zero point of the temperature scale, which should not have larger than ±0.10 mag effect on the distance modulus.