Calibrating the Galactic Cepheid Period-Luminosity relation from the maximum-likelihood technique

Abstract

We present a realization of the maximum-likelihood (ML) technique, which is one of the latest modifications of the Baade--Becker--Wesselink (BBW) method. Our approach is based on non-linear calibrations of the effective temperature and bolometric correction which take into account metallicity and surface gravity. It allows one to estimate the key Cepheid parameters, the distance modulus, and the interstellar reddening, combining photometric and spectroscopic data (including the effective temperature data). This method is applied to a sample of 44 Galactic Cepheids, for which multiphase temperature measurements are available. The additional data correction is performed to subtract the impact of the component in binary/multiple systems. We also study the effect of shock waves, whose presence in the stellar atmosphere distorts the observational data and leads to systematic errors in the obtained parameters. We determine the optimal restriction on the input data to eliminate this effect. This restriction provides accurate period-radius and period-luminosity relations which are consistent with the results in previous studies. We found the following relations: $log\,R = (0.68 \pm 0.03) \cdot log\,P + (1.14 \pm 0.03)$, $M_v = - (2.67 \pm 0.16) \cdot (log\,P - 1) - (4.14 \pm 0.05)$.