Absolute-Magnitude Calibration for W~UMa-type Systems. II. Influence of Metallicity

Abstract

A modification to the absolute magnitude calibration for W~UMa-type systems, taking into account differences in metal abundances, is derived on the basis of contact binary systems recently discovered in metal-poor clusters. A preliminary estimate of the magnitude of the metallicity-dependent term for the $(B-V)$-based calibration is $\Delta M_V = -(0.3 \pm 0.1) \times [Fe/H]$. The calibration based on the $(V-I_C)$ color is expected to be less sensitive with the correction term $\approx -(0.12\pm 0.05) \times [Fe/H]$.