2010A&A...521A..40A

Several large scale photometric and spectroscopic surveys are being undertaken to provide a more detailed picture of the Milky Way. Given the necessity of generalisation in the determination of, e.g., stellar parameters when tens and hundred of thousands of stars are considered it remains important to provide independent, detailed studies to verify the methods used in the surveys. Our first aim is to critically evaluate available calibrations for deriving [M/H] from Stroemgren photometry. Secondly, we develop the standard sequences for dwarf stars to reflect their inherent metallicity dependence. Finally, we test how well metallicities derived from ugriz photometry reproduce metallicities derived from the well-tested system of Stroemgren photometry. We evaluate available metallicity calibrations based on Stroemgren uvby photometry for dwarf stars using a catalogue of stars with both uvby photometry and spectroscopically determined iron abundances ([Fe/H]). The catalogue was created for this project. Using this catalogue, we also evaluate available calibrations that determine logg. A larger catalogue, in which metallicity is determined directly from uvby photometry, is used to trace metallicity-dependent standard sequences for dwarf stars. We also perform comparisons, for both dwarf and giant stars, of metallicities derived from ugriz photometry with metallicities derived from Stroemgren photometry. We provide a homogenised catalogue of 451 dwarf stars with 0.3<(b-y)₀<1.0. All stars in the catalogue have uvby photometry and [Fe/H] determined from spectra with high resolution and high signal-to-noise ratios (S/N). Using this catalogue, we test how well various photometric metallicity calibrations reproduce the spectroscopically determined [Fe/H]. Using the preferred metallicity calibration for dwarf stars, we derive new standard sequences in the c_1,0 versus (b-y)₀ plane and in the c_1,0 versus (v-y)₀ plane for dwarf stars with 0.40<(b-y)₀<0.95 and 1.10<(v-y)₀<2.38. We recommend the calibrations of Ramirez & Melendez (2005ApJ...626..446R, 2005ApJ...626..465R) in deriving metallicities from Stroemgren photometry and find that intermediate band photometry, such as Stroemgren photometry, more accurately than broad band photometry reproduces spectroscopically determined [Fe/H]. Stroemgren photometry is also better at differentiating between dwarf and giant stars. We conclude that additional investigations of the differences between metallicities derived from ugriz photometry and intermediate-band photometry, such as Stroemgren photometry, are required.