New metallicity calibration down to [Fe/H]=-2.75 dex

Abstract

We have taken 88 dwarfs, covering the colour-index interval 0.37 less than or equal to (B-V)(0) less than or equal to 1.07 mag, with metallicities - 2.70 less than or equal to [Fe/H] less than or equal to + 0.26 dex, from three different sources for new metallicity calibration. The catalogue of Cayrel de Strobel et al. ( 2001), which includes 65% of the stars in our sample, supplies detailed information on abundances for stars with determination based on high-resolution spectroscopy. In constructing the new calibration we have used as 'corner stones' 77 stars which supply at least one of the following conditions: (i) the parallax is larger than 10 mas ( distance relative to the Sun less than 100 pc) and the galactic latitude is absolutely higher than 30degrees; (ii) the parallax is rather large, if the galactic latitude is absolutely low and vice versa. Contrary to previous investigations, a third-degree polynomial is fitted for the new calibration: [Fe/H]= 0.10 - 2.76delta - 24.04delta(2) + 30.00delta(3). The coefficients were evaluated by the least-squares method, without regard to the metallicity of Hyades. However, the constant term is in the range of metallicity determined for this cluster, i.e. 0.08 less than or equal to [Fe/ H] less than or equal to 0.11 dex. The mean deviation and the mean error in our work are equal to those of Carney (1979), for [Fe/H] greater than or equal to - 1.75 dex where Carney's calibration is valid.