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uvby-? photometry of solar twins . The solar colors, model atmospheres, and the Teff and metallicity scales
Aims: Solar colors have been determined on the uvby-?photometric system to test absolute solar fluxes, to examine colorspredicted by model atmospheres as a function of stellar parameters(Teff, log g, [Fe/H]), and to probe zero-points ofTeff and metallicity scales. Methods: New uvby-?photometry is presented for 73 solar-twin candidates. Most stars of oursample have also been observed spectroscopically to obtain accuratestellar parameters. Using the stars that most closely resemble the Sun,and complementing our data with photometry available in the literature,the solar colors on the uvby-? system have been inferred. Our solarcolors are compared with synthetic solar colors computed from absolutesolar spectra and from the latest Kurucz (ATLAS9) and MARCS modelatmospheres. The zero-points of different Teff andmetallicity scales are verified and corrections are proposed. Results: Our solar colors are (b-y)? = 0.4105 ±0.0015, m1, ? = 0.2122 ± 0.0018, c1,? = 0.3319 ± 0.0054, and ?? =2.5915 ± 0.0024. The (b-y)? and m1,? colors obtained from absolute spectrophotometry of the Sunagree within 3-? with the solar colors derived here when thephotometric zero-points are determined from either the STIS HSTobservations of Vega or an ATLAS9 Vega model, but the c1,? and ?? synthetic colors inferred fromabsolute solar spectra agree with our solar colors only when thezero-points based on the ATLAS9 model are adopted. The Kurucz solarmodel provides a better fit to our observations than the MARCS model.For photometric values computed from the Kurucz models,(b-y)? and m1, ? are in excellentagreement with our solar colors independently of the adoptedzero-points, but for c1, ? and ??agreement is found only when adopting the ATLAS9 zero-points. Thec1, ? color computed from both the Kurucz and MARCSmodels is the most discrepant, probably revealing problems either withthe models or observations in the u band. The Teffcalibration of Alonso and collaborators has the poorest performance(~140 K off), while the relation of Casagrande and collaborators is themost accurate (within 10 K). We confirm that the Ramírez &Meléndez uvby metallicity calibration, recommended byÁrnadóttir and collaborators to obtain [Fe/H] in F, G, andK dwarfs, needs a small (~10%) zero-point correction to place the starsand the Sun on the same metallicity scale. Finally, we confirm that thec1 index in solar analogs has a strong metallicitysensitivity.Based on observations collected at the H. L. Johnson 1.5 m telescope atthe Observatorio Astronómico Nacional at San Pedro Mártir,Baja California, México.Tables 1-3 and 5 are only available inelectronic form at http://www.aanda.org
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