Ba. Twarog et Bj. Anthonytwarog, DDO METALLICITY CALIBRATION FOR METAL-DEFICIENT RED GIANTS AND THE DISK-HALO TRANSITION, The Astronomical journal, 107(4), 1994, pp. 1371-1380
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].