[Fe/H] from RR Lyrae light curves

The method introduces a considerable improvement relative to our previously published formulae. First of all, it uses an improved and extended data base for the light curves and more accurate, very recent iron abundances.

Secondly, the new data base makes it possible to show that the basic relation between [Fe/H] and the Fourier parameters is linear and contains only the period and one of the Fourier phases, most importantly {phi}_31_. Last but not least, we derive interrelations among the Fourier parameters which help us to filter out peculiar stars where more caution is needed in accepting the calculated abundance. The applicability of the method is demonstrated on independent samples of globular cluster stars.