========================================================================== II/180 uvby-beta photometry of metal-poor stars (Schuster+ 1989) The following files can be converted to FITS (extension .fit .fit.Z .fgz) table1 ========================================================================== Query from: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/180 ==========================================================================
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Beginning of ReadMe : II/180 uvby-beta photometry of metal-poor stars (Schuster+ 1989) ================================================================================ uvby-beta photometry of high-Velocity and metal-poor stars Schuster W.J., Nissen P.E. <Astron. Astrophys. 222, 69 (1989)> =1989A&A...222...69S ================================================================================ ADC_Keywords: Stars, high-velocity ; Stars, metal-deficient Keywords: evolution of the Galaxy - halo stars - metallicity - ages Description: Using the calibrations derived by Schuster and Nissen (=1989A&A...221...65S), the interstellar color excesses, E(b-y), and the metallicities, [Fe/H], have been determined for the 711 high velocity and metal-poor stars in the catalogue of uvby-beta photometry (=1988A&AS...73..225S). 220 of these listed in table1 turn out to be halo stars according to the criterion [Fe/H] <= -1.0. About 15% of the halo stars have colors that are significantly affected by interstellar reddening, i.e. E(b-y) > 0.025. The distributions in the c0-(b-y)0 diagram of the halo stars grouped according to [Fe/H], have well defined turn-off points. From the Teff values of these points a minimum age of 18-20 Gyr for the halo stars is determined. However, this age may be 2-3 Gyr too high due to a possible systematic error in Teff for the stellar models used. Relative ages of 77 halo stars in the turn-off region of the c0-(b-y)0 diagram are derived using the isochrones VandenBerg and Bell (=1985ApJS...58..561V). Assuming that the O/Fe abundance ratio is constant in halo stars, evidence of a cosmic age scatter of +/-2.5Gyr at a given metallicity is found. Furthermore, the mean age of the halo stars is found to decrease smoothly by about 3 Gyr from [Fe/H]= -2.0 to -1.0. These results suggest that a pressure-supported slow uniform collapse controlled the formation and early evolution of the Galaxy. However, the scenario of Searle and Zinn (=1978ApJ...225..357S) is also compatible with the results.