DDO METALLICITY CALIBRATION FOR METAL-DEFICIENT RED GIANTS AND THE DISK-HALO TRANSITION

DDO abundance estimates for metal-deficient field red giants from the survey by Norris et al. [ApJS, 58, 463 (1985)] are compared with high dispersion spectroscopic abundances and recalibrated uvby photometry. The DDO abundances are shown to deviate from the standard system by an amount which is metallicity dependent, i.e., a simple offset cannot t ransform the DDO data to the spectroscopic system. A recalibration of the DDO photometry demonstrates that the old DDO calibration provides reliable [Fe/H] estimates near -0.8 and -2.3, but systematically under estimates the metallicity of stars near -1.2 by about 0.5 dex. Reanaly sis of the red giant sample of Norris et al. leads to a metallicity di stribution much closer to that of the globular clusters while signific antly decreasing the fraction of metal-weak disk stars. A possible exp lanation for origin of the discrepancy is that the clusters of interme diate [Fe/H] used in the DDO calibration are not representative of the field stars at the same [Fe/H].