The ability of intermediate-band Str?mgren photometry to correctly identify dwarf, subgiant, and giant stars and provide stellar metallicities and surface gravities

摘要

Context. Several large scale photometric andspectroscopic surveys are being undertaken to provide a more detailedpicture of the MilkyWay. Given the necessity ofgeneralisation in the determination of, e.g., stellar parameters whentens and hundred of thousands of stars are considered it remainsimportant to provide independent, detailed studies to verify themethods used in the surveys. Aims. Our first aim is to critically evaluateavailable calibrations for deriving [M/H] from Str?mgren photometry.Secondly, we develop the standard sequences for dwarf stars to reflecttheir inherent metallicity dependence. Finally, we test how wellmetallicities derived from ugrizphotometryreproduce metallicities derived from the well-tested system ofStr?mgren photometry. Methods. We evaluate available metallicitycalibrations based on Str?mgren uvbyphotometryfor dwarf stars using a catalogue of stars with both uvbyphotometryand spectroscopically determined iron abundances([Fe/H]). Thecatalogue was created for this project. Using this catalogue, we alsoevaluate available calibrations that determine.Alarger catalogue, in which metallicity is determineddirectly from uvbyphotometry,isused to trace metallicity-dependent standard sequences fordwarf stars. We also perform comparisons, for both dwarf and giantstars, ofmetallicities derived from ugrizphotometrywith metallicities derived from Str?mgren photometry. Results. We provide a homogenised catalogue of 451dwarf stars with0.3<(b-y)0<1.0.All stars in the catalogue have uvbyphotometryand [Fe/H] determined from spectra with high resolution and highsignal-to-noise ratios (S/N). Using this catalogue, we test how wellvarious photometric metallicity calibrations reproduce thespectroscopically determined [Fe/H]. Using the preferred metallicitycalibration for dwarf stars, we derive new standard sequences in the c1,0versus(b-y)0planeand in the c1,0versus(v-y)0planefor dwarf stars with0.40 < (b-y)0< 0.95 and1.10 < (v-y)0< 2.38. Conclusions. We recommend the calibrations ofRamírez & Meléndez (2005) in deriving metallicities fromStr?mgren photometry and find that intermediate band photometry,suchas Str?mgren photometry, more accurately than broad bandphotometry reproduces spectroscopically determined [Fe/H]. Str?mgrenphotometry is also better at differentiating between dwarf and giantstars. We conclude that additional investigations of the differencesbetween metallicities derived from ugrizphotometryand intermediate-band photometry, such as Str?mgren photometry, arerequired. Key words: stars: abundances - stars:fundamental parameters - solar neighborhood - Galaxy: stellar content